Metallothionein and brain inflammation

Functional regulation of microglia by vitamin B12 alleviates ischemic stroke-induced neuroinflammation in mice

Ischemic stroke is the second leading cause of death and disability worldwide, and efforts to prevent stroke, mitigate secondary neurological damage, and promote neurological recovery remain paramount. Recent findings highlight the critical importance of microbiome-related metabolites, including vitamin B12 (VB12), in alleviating toxic stroke-associated neuroinflammation. Here, we showed that VB12 tonically programmed genes supporting microglial cell division and activation and critically controlled cellular fatty acid metabolism in homeostasis. Intriguingly, VB12 promoted mitochondrial transcriptional and metabolic activities and significantly restricted stroke-associated gene alterations in microglia. Furthermore, VB12 differentially altered the functions of microglial subsets during the acute phase of ischemic stroke, resulting in reduced brain damage and improved neurological function. Pharmacological depletion of microglia before ischemic stroke abolished VB12-mediated neurological improvement. Thus, our preclinical studies highlight the relevance of VB12 in the functional programming of microglia to alleviate neuroinflammation, minimize ischemic injury, and improve host neurological recovery after ischemic stroke.

Using Redox Proteomics to Gain New Insights into Neurodegenerative Disease and Protein Modification

Antioxidant defenses in biological systems ensure redox homeostasis, regulating baseline levels of reactive oxygen and nitrogen species (ROS and RNS). Oxidative stress (OS), characterized by a lack of antioxidant defenses or an elevation in ROS and RNS, may cause a modification of biomolecules, ROS being primarily absorbed by proteins. As a result of both genome and environment interactions, proteomics provides complete information about a cell's proteome, which changes continuously. Besides measuring protein expression levels, proteomics can also be used to identify protein modifications, localizations, the effects of added agents, and the interactions between proteins. Several oxidative processes are frequently used to modify proteins post-translationally, including carbonylation, oxidation of amino acid side chains, glycation, or lipid peroxidation, which produces highly reactive alkenals. Reactive alkenals, such as 4-hydroxy-2-nonenal, are added to cysteine (Cys), lysine (Lys), or histidine (His) residues by a Michael addition, and tyrosine (Tyr) residues are nitrated and Cys residues are nitrosylated by a Michael addition. Oxidative and nitrosative stress have been implicated in many neurodegenerative diseases as a result of oxidative damage to the brain, which may be especially vulnerable due to the large consumption of dioxygen. Therefore, the current methods applied for the detection, identification, and quantification in redox proteomics are of great interest. This review describes the main protein modifications classified as chemical reactions. Finally, we discuss the importance of redox proteomics to health and describe the analytical methods used in redox proteomics.

Metallothionein expression in the central nervous system in response to chronic heavy metal exposure: possible neuroprotective mechanism

It has been reported that volcanoes release several tonnes of mercury per year among other heavy metals through eruptions, fumaroles, or diffuse soil degassing. Since a high percentage of the world's population lives in the vicinity of an active volcano, the aim of this study is to evaluate the accumulation of these metals in the central nervous system and the presence of cellular mechanisms of heavy metal detoxification such as metallothioneins. To carry out this study, wild mice (Mus musculus) chronically exposed to an active volcanic environment were captured in Furnas village (Azores, Portugal) and compared with those trapped in a reference area (Rabo de Peixe, Azores, Portugal). On the one hand, the heavy metal load has been evaluated by analyzing brain and cerebellum using ICP-MS and a mercury analyzer and on the other hand, the presence of metallothionein 2A has been studied by immunofluorescence assays. Our results show a higher load of metals such as mercury, cadmium and lead in the central nervous system of exposed mice compared to non-exposed individuals and, in addition, a higher immunoreactivity for metallothionein 2A in different areas of the cerebrum and cerebellum indicating a possible neuroprotection process.

Zinc and Central Nervous System Disorders

Zinc (Zn²⁺) is the second most abundant necessary trace element in the human body, exerting a critical role in many physiological processes such as cellular proliferation, transcription, apoptosis, growth, immunity, and wound healing. It is an essential catalyst ion for many enzymes and transcription factors. The maintenance of Zn²⁺ homeostasis is essential for the central nervous system, in which Zn²⁺ is abundantly distributed and accumulates in presynaptic vesicles. Synaptic Zn²⁺ is necessary for neural transmission, playing a pivotal role in neurogenesis, cognition, memory, and learning. Emerging data suggest that disruption of Zn²⁺ homeostasis is associated with several central nervous system disorders including Alzheimer's disease, depression, Parkinson's disease, multiple sclerosis, schizophrenia, epilepsy, and traumatic brain injury. Here, we reviewed the correlation between Zn²⁺ and these central nervous system disorders. The potential mechanisms were also included. We hope that this review can provide new clues for the prevention and treatment of nervous system disorders.

Oxidative stress and neuroimmune proteins in a mouse model of autism

Oxidative stress including decreased antioxidant enzyme activities, elevated lipid peroxidation, and accumulation of advanced glycation end products in the blood from children with autism spectrum disorders (ASD) has been reported. The mechanisms affecting the development of ASD remain unclear; however, toxic environmental exposures leading to oxidative stress have been proposed to play a significant role. The BTBRT+Itpr3tf/J (BTBR) strain provides a model to investigate the markers of oxidation in a mouse strain exhibiting ASD-like behavioral phenotypes. In the present study, we investigated the level of oxidative stress and its effects on immune cell populations, specifically oxidative stress affecting surface thiols (R-SH), intracellular glutathione (iGSH), and expression of brain biomarkers that may contribute to the development of the ASD-like phenotypes that have been observed and reported in BTBR mice. Lower levels of cell surface R-SH were detected on multiple immune cell subpopulations from blood, spleens, and lymph nodes and for sera R-SH levels of BTBR mice compared to C57BL/6 J (B6) mice. The iGSH levels of immune cell populations were also lower in the BTBR mice. Elevated protein expression of GATA3, TGM2, AhR, EPHX2, TSLP, PTEN, IRE1α, GDF15, and metallothionein in BTBR mice is supportive of an increased level of oxidative stress in BTBR mice and may underpin the pro-inflammatory immune state that has been reported in the BTBR strain. Results of a decreased antioxidant system suggest an important oxidative stress role in the development of the BTBR ASD-like phenotype.

Importance of Genetic Polymorphisms in MT1 and MT2 Genes in Metals Homeostasis and Their Relationship with the Risk of Acute Pancreatitis Occurrence in Smokers-Preliminary Findings

This study was aimed at evaluating the changes in metallothionein (MT) concentration in the blood of patients with acute pancreatitis (AP) and healthy subjects, taking into account the extracellular (plasma) and intracellular (erythrocyte lysate) compartments. The impact of single-nucleotide polymorphisms (SNPs) in the MT1A (rs11640851), MT1B (rs964372) and MT2A (rs10636) genes on MT concentration and their association with the concentration of metals (Cu, Zn, Cd) and ceruloplasmin as Cu-related proteins were analyzed. The concentration of a high-sensitivity C-reactive protein (hs-CRP) and IL-6 as markers of inflammation, and malonyldialdehyde (MDA), superoxide dismutase (SODs) activity and the value of total antioxidant capacity (TAC) as parameters describing the pro/antioxidative balance were also assessed. In the AP patient groups, an increased MT concentration in erythrocyte lysate compared to healthy subjects was shown, especially in individuals with the GG genotype for rs964372 in the MT1B gene. A Zn concentration was especially decreased in the blood of smoking AP patients with the AA genotype for SNP rs11640851 in the MT1A gene and the GC genotype for SNP rs10636 in MT2A, compared to non-smokers with AP, which was accompanied by an increase in the value of the Cu/Zn ratio. The exposure to tobacco smoke xenobiotics increased the risk of AP occurrence in subjects with the CC genotype for SNP rs11640851 in the MT1A gene by more than fourfold. The investigated polymorphisms, rs11640851 in the MT1A gene, rs964372 in the MT1B gene and rs10636 in the MT2A gene, seem to be an important factor in maintaining homeostasis in an organism under oxidative stress conditions.

The Function of Transthyretin Complexes with Metallothionein in Alzheimer's Disease

Alzheimer’s disease (AD) is one of the most frequently diagnosed types of dementia in the elderly. An important pathological feature in AD is the aggregation and deposition of the β-amyloid (Aβ) in extracellular plaques. Transthyretin (TTR) can cleave Aβ, resulting in the formation of short peptides with less activity of amyloid plaques formation, as well as being able to degrade Aβ peptides that have already been aggregated. In the presence of TTR, Aβ aggregation decreases and toxicity of Aβ is abolished. This may prevent amyloidosis but the malfunction of this process leads to the development of AD. In the context of Aβplaque formation in AD, we discuss metallothionein (MT) interaction with TTR, the effects of which depend on the type of MT isoform. In the brains of patients with AD, the loss of MT-3 occurs. On the contrary, MT-1/2 level has been consistently reported to be increased. Through interaction with TTR, MT-2 reduces the ability of TTR to bind to Aβ, while MT-3 causes the opposite effect. It increases TTR-Aβ binding, providing inhibition of Aβ aggregation. The protective effect, assigned to MT-3 against the deposition of Aβ, relies also on this mechanism. Additionally, both Zn₇MT-2 and Zn₇MT-3, decrease Aβ neurotoxicity in cultured cortical neurons probably because of a metal swap between Zn₇MT and Cu(II)Aβ. Understanding the molecular mechanism of metals transfer between MT and other proteins as well as cognition of the significance of TTR interaction with different MT isoforms can help in AD treatment and prevention.

The influence of metallothionein treatment and treadmill running exercise on disease onset and survival in SOD1G93A amyotrophic lateral sclerosis mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, characterised by the degeneration of motor neurons innervating skeletal muscle. The mechanisms underlying neurodegeneration in ALS are not yet fully elucidated, and with current therapeutics only able to extend lifespan by a matter of months there is a clear need for novel therapies to increase lifespan and patient quality of life. Here, we evaluated whether moderate-intensity treadmill exercise and/or treatment with metallothionein-2 (MT2), a neuroprotective protein, could improve survival, behavioural or neuropathological outcomes in SOD1^G93A familial ALS mice. Six-week-old female SOD1^G93A mice were allocated to one of four treatment groups: MT2 injection, i.m.; moderate treadmill exercise; neither MT2 nor exercise; or both MT2 and exercise. MT2-treated mice survived around 3% longer than vehicle-treated mice, with this mild effect reaching statistical significance in Cox proportional hazards analysis once adjusted for potential confounders. Mixed model body weight trajectories over time indicated that MT2-treated mice, with or without exercise, reached maximum body weight at a later age, suggesting a delay in disease onset of around 4% compared to saline-treated mice. Exercise alone did not significantly increase survival or delay disease onset, and neither exercise nor MT2 substantially ameliorated gait abnormalities or muscle strength loss. We conclude that neither exercise nor MT2 treatment was detrimental in female SOD1^G93A mice, and further study could determine whether the mild effect of peripheral MT2 administration on disease onset and survival could be improved via direct administration of MT2 to the central nervous system.

Role of Zinc in Immune System and Anti-Cancer Defense Mechanisms

The human body cannot store zinc reserves, so a deficiency can arise relatively quickly, e.g., through an improper diet. Severe zinc deficiency is rare, but mild deficiencies are common around the world. Many epidemiological studies have shown a relationship between the zinc content in the diet and the risk of cancer. The anti-cancer effect of zinc is most often associated with its antioxidant properties. However, this is just one of many possibilities, including the influence of zinc on the immune system, transcription factors, cell differentiation and proliferation, DNA and RNA synthesis and repair, enzyme activation or inhibition, the regulation of cellular signaling, and the stabilization of the cell structure and membranes. This study presents selected issues regarding the current knowledge of anti-cancer mechanisms involving this element.

CuII(atsm) Attenuates Neuroinflammation

Background: Neuroinflammation and biometal dyshomeostasis are key pathological features of several neurodegenerative diseases, including Alzheimer’s disease (AD). Inflammation and biometals are linked at the molecular level through regulation of metal buffering proteins such as the metallothioneins. Even though the molecular connections between metals and inflammation have been demonstrated, little information exists on the effect of copper modulation on brain inflammation.

Methods: We demonstrate the immunomodulatory potential of the copper bis(thiosemicarbazone) complex Cu^II(atsm) in an neuroinflammatory model in vivo and describe its anti-inflammatory effects on microglia and astrocytes in vitro.

Results: By using a sophisticated in vivo magnetic resonance imaging (MRI) approach, we report the efficacy of Cu^II(atsm) in reducing acute cerebrovascular inflammation caused by peripheral administration of bacterial lipopolysaccharide (LPS). Cu^II(atsm) also induced anti-inflammatory outcomes in primary microglia [significant reductions in nitric oxide (NO), monocyte chemoattractant protein 1 (MCP-1), and tumor necrosis factor (TNF)] and astrocytes [significantly reduced NO, MCP-1, and interleukin 6 (IL-6)] in vitro. These anti-inflammatory actions were associated with increased cellular copper levels and increased the neuroprotective protein metallothionein-1 (MT1) in microglia and astrocytes.

Conclusion: The beneficial effects of Cu^II(atsm) on the neuroimmune system suggest copper complexes are potential therapeutics for the treatment of neuroinflammatory conditions.

Expression and regulation of metallothioneins in myometrium and fetal membranes

PROBLEM

Metallothioneins (MTs) play important roles in regulating oxidative stress, inflammation, and hormone signaling. These processes play a major role in labor at term and preterm. The aims of this study were to characterize (a) temporal- and labor-associated changes and (b) the effect of pro-inflammatory and pro-labor insults on the expression of MT1 isoforms, MT2A, MT3, and MT4 in fetal membranes and myometrium.

METHOD OF STUDY

The expression of MTs was assessed in fetal membranes and myometrium from nonlaboring and laboring women at preterm and term by RT-qPCR. Tissue explants were used to assess the effect of pro-inflammatory cytokines and Toll-like receptor (TLR) ligands on the expression of MTs in fetal membranes and myometrium.

RESULTS

In fetal membranes, the expression of MT1A, MT1E, MT1F, MT1X, and MT2A was higher at term compared with preterm. Preterm labor and preterm histological chorioamnionitis were associated with increased expression of MT1A, MT1G, MT1M, MT1X, MT2A, and MT3. Term labor was associated with increased expression of MT1A, MT1F, MT1X, MT2A, and MT3 in fetal membranes and expression of MT1A, MT1E, MT1F, MT1G, MT1M, MT1X, MT2A, and MT3 in myometrium. Pro-inflammatory cytokines and TLR ligands increased the expression of MT1A, MT1E, MT1F, MT1G, MT1H, MT1X, and MT2A in fetal membranes and myometrium.

CONCLUSION

Temporal-, labor-, and infection-associated increases in MT1 isoforms, MT2A, and MT3 have been observed in fetal membranes and/or myometrium. Furthermore, pro-inflammatory cytokines and bacterial and viral products increased the expression of MT1 isoforms, MT2A, MT3, and MT4 mRNA expression in fetal membranes and myometrium.

Expression Profiles of Metallothionein I/II and Megalin in Cuprizone Model of De- and Remyelination

Copper chelator cuprizone (CPZ) is neurotoxicant, which selectively disrupts oligodendroglial respiratory chain, leading to oxidative stress and subsequent apoptosis. Demyelination is, however, followed by spontaneous remyelination owing to the activation of intrinsic CNS repair mechanisms. To explore the participation of metallothioneins (MTs) in these processes, in this study we analyzed the expression profiles of MT-I/II and their receptor megalin (low-density lipoprotein receptor related protein-2) in the brain of mice subjected to different protocols of CPZ feeding. Experiments were performed in female C57BL/6 mice fed with 0.25% CPZ during 1, 3 and 5 weeks. They were sacrificed immediately after feeding with CPZ or 2 weeks after the withdrawal of CPZ. The data showed that CPZ-induced demyelination was followed by high astrogliosis and enhanced expression of MTs and megalin in white (corpus callosum and internal capsule) and gray matter of the brain (cortex, hippocampus, and cerebellum). Moreover, in numerous cortical neurons and progenitor cells the signs of MT/megalin interactions and Akt1 phosphorylation was found supporting the hypothesis that MTs secreted from the astrocytes might directly affect the neuronal differentiation and survival. Furthermore, in mice treated with CPZ for 5 weeks the prominent MTs and megalin immunoreactivities were found on several neural stem cells and oligodendrocyte progenitors in subgranular zone of dentate gyrus and subventricular zone of lateral ventricles pointing to high modulatory effect of MTs on adult neuro- and oligodendrogenesis. The data show that MT I/II perform important cytoprotective and growth-regulating functions in remyelinating processes activated after toxic demyelinating insults.

The neuronal protection of a zinc-binding protein isolated from oyster

Mitochondrial function is applied as oxidative stress and neuronal damage index. In this study, d-galactose was used to induce free radicals production and neuronal damage in HN-h cells, and the effect of novel 43 kDa protein isolated from oyster on anti-mitochondrial dysfunction and zinc-binding ability were evaluated. Crystal violet stain results indicated zinc-binding protein of oyster (ZPO) attenuated neuronal cell death induced by 100 mM of d-galactose on HN-h cells in a dose-dependent manner. ZPO alleviated mitochondrial inactivation, mitochondrial membrane potential decreasing, oxidative stress, and fusion/fission state in non-cytotoxic concentration of d-galactose (50 mM)-treated HN-h cells. ZPO treatment recovered metallathionein-3 (MT-3) decrease and inhibited β- and γ-secretase as well as amyloid beta (Aβ) accumulation in HN-h cells caused by d-galactose induction. These results suggest ZPO could avoid oxidative stress and is a functional protein for zinc concentration maintainability, which has potential for development of functional foods for neuronal protection.

Zinc Signal in Brain Diseases

The divalent cation zinc is an integral requirement for optimal cellular processes, whereby it contributes to the function of over 300 enzymes, regulates intracellular signal transduction, and contributes to efficient synaptic transmission in the central nervous system. Given the critical role of zinc in a breadth of cellular processes, its cellular distribution and local tissue level concentrations remain tightly regulated via a series of proteins, primarily including zinc transporter and zinc import proteins. A loss of function of these regulatory pathways, or dietary alterations that result in a change in zinc homeostasis in the brain, can all lead to a myriad of pathological conditions with both acute and chronic effects on function. This review aims to highlight the role of zinc signaling in the central nervous system, where it may precipitate or potentiate diverse issues such as age-related cognitive decline, depression, Alzheimer's disease or negative outcomes following brain injury.

Trace elements in unconventional animals: A 40-year experience

The role of trace elements in animal health has attracted increasing interest in recent years. The essentiality and toxicity of these elements have been extensively investigated in humans, laboratory animal models and partially in domestic animals, whereas little is known about trace element metabolism in most living organisms. Forty years ago our research started on Cd metabolism in molluscs, thereafter expanding to Zn, Cu, and Fe metabolism in many unconventional animal species of veterinary interest. This review summarizes the main results obtained over this long period of time: some of the findings are original and have not been published to date. They are discussed in more detail and compared with data obtained in conventional animals, including man.

Metallothionein, Copper and Alpha-Synuclein in Alpha-Synucleinopathies

Metallothioneins (MTs) are proteins that function by metal exchange to regulate the bioavailability of metals, such as zinc and copper. Copper functions in the brain to regulate mitochondria, neurotransmitter production, and cell signaling. Inappropriate copper binding can result in loss of protein function and Cu(I)/(II) redox cycling can generate reactive oxygen species. Copper accumulates in the brain with aging and has been shown to bind alpha-synuclein and initiate its aggregation, the primary aetiological factor in Parkinson's disease (PD), and other alpha-synucleinopathies. In PD, total tissue copper is decreased, including neuromelanin-bound copper and there is a reduction in copper transporter CTR-1. Conversely cerebrospinal fluid (CSF) copper is increased. MT-1/2 expression is increased in activated astrocytes in alpha-synucleinopathies, yet expression of the neuronal MT-3 isoform may be reduced. MTs have been implicated in inflammatory states to perform one-way exchange of copper, releasing free zinc and recent studies have found copper bound to alpha-synuclein is transferred to the MT-3 isoform in vitro and MT-3 is found bound to pathological alpha-synuclein aggregates in the alpha-synucleinopathy, multiple systems atrophy. Moreover, both MT and alpha-synuclein can be released and taken up by neural cells via specific receptors and so may interact both intra- and extra-cellularly. Here, we critically review the role of MTs in copper dyshomeostasis and alpha-synuclein aggregation, and their potential as biomarkers and therapeutic targets.

Osteopontin-metallothionein I/II interactions in experimental autoimmune encephalomyelitis

Osteopontin (OPN), an extracellular matrix (ECM) glyco-phosphoprotein, plays an important role in autoimmune-mediated demyelinating diseases, including multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). As an integrin and CD44 binding protein it participates in bidirectional communication between the ECM and target cells and affects transduction pathways that maintain neuronal and immune cell homeostasis. Its biological activity is also heavily influenced by microenvironment, which stimulates the cleavage of OPN and changes its functions. In this study we estimated the expression profile of OPN in neural tissues of DA rats during the first relapse of chronic relapsing EAE and investigated the relationship of OPN to metallothionein I+II (MTs), which play pivotal role in zinc-related cell homeostasis and in protection of CNS against cytokine-induced injury. The data showed that in EAE rats OPN mRNA and protein levels increased concurrently with the transcription of MTs and that within the spinal cord (SC) lysates EAE-afflicted rats had a higher content of OPN fragments of low molecular weight than untreated and CFA-treated rats. The expression of OPN and MTs was upregulated on ependymal, lymphoid and astroglial cells and on multiple αvβ3+ neurons in SC and in the brain (cortex, white matter, hippocampus, and cerebellum). Besides, multiple cells co-expressed OPN and MTs. Granular OPN signals were detected in secretory vesicles of Golgy (αvβ3 neurons) and in patches adjacent to the plasma membrane (subventricular zone). The findings imply that in demyelinating lesions are generated proteolytic OPN fragments and that OPN/MT interactions contribute to tissue remodeling during an autoimmune attack.

Role of Metallothionein in Post-Burn Inflammation

Metallothioneins (MTs) are a family of low molecular-weight and cysteine-rich metalloproteins that regulate metal metabolism and protect cells from oxygen free radicals. Recent studies suggested that MTs have some anti-inflammatory effects. However, the role of MTs in post-burn inflammation remains unclear. This study is designed to investigate the role of MTs in post-burn inflammation in a mouse burn model. MT-I/II null (-/-) and C57BL/6 wild-type (WT) mice were randomly divided into sham burn, burn, Zn treated, and Zn-MT-2 treated groups. The inflammatory cytokines levels were measured by enzyme-linked immunosorbent assay (ELISA). Myeloperoxidase (MPO) activity was determined by spectrophotometry. In in vitro study, exogenous MT-2 was added to macrophages that were stimulated with burn serum in the presence or absence of a p38 MAPK inhibitor SB203580. The IL-6 and TNF-α messenger RNA (mRNA) expression were detected by quantitative real-time polymerase chain reaction. The levels of p38 expression were determined by Western blot. Burn induced increased inflammatory cytokines such as interleukin (IL)-1β, IL-6, tumor necrosis factors-α, and macrophage chemoattractant protein-1 production in burn wound and serum. The MPO activities in the lung and heart were also increased after burn. These effects were significantly more prominent in MT (-/-) mice than in WT mice. Furthermore, these effects were inhibited by administration of exogenous MT-2 to both WT and MT (-/-) mice. Exogenous MT-2 inhibited the p38 expression and abrogated the increase of IL-6 and TNF-α mRNA expression from macrophages that were stimulated with burn serum. The effect of MT-2 was not further strengthened in the presence of SB203580. MTs may have a protective role against post-burn inflammation and inflammatory organ damage, at least partly through inhibiting the p38 MAPK signaling.

Overexpression of Metallothionein-1 Modulates the Phenotype of the Tg2576 Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most commonly diagnosed dementia, where signs of neuroinflammation and oxidative stress are prominent. In this study we intend to further characterize the roles of the antioxidant, anti-inflammatory, and heavy metal binding protein, metallothionein-1 (MT-1), by crossing Mt1 overexpressing mice with a well-known mouse model of AD, Tg2576 mice, which express the human amyloid-β protein precursor (hAβPP) with the Swedish K670N/M671L mutations. Mt1 overexpression increased overall perinatal survival, but did not affect significantly hAβPP-induced mortality and weight loss in adult mice. Amyloid plaque burden in ∼14-month-old mice was increased by Mt1 overexpression in the hippocampus but not the cortex. Despite full length hAβPP levels and amyloid plaques being increased by Mt1 overexpression in the hippocampus of both sexes, oligomeric and monomeric forms of Aβ, which may contribute more to toxicity, were decreased in the hippocampus of females and increased in males. Several behavioral traits such as exploration, anxiety, and learning were altered in Tg2576 mice to various degrees depending on the age and the sex. Mt1 overexpression ameliorated the effects of hAβPP on exploration in young females, and potentiated those on anxiety in old males, and seemed to improve the rate of spatial learning (Morris water maze) and the learning elicited by a classical conditioning procedure (eye-blink test). These results clearly suggest that MT-1 may be involved in AD pathogenesis.

Exposure to ambient ultrafine particulate matter alters the expression of genes in primary human neurons

Exposure to ambient particulate matter (PM) has been associated with the onset of neurodevelopmental and neurodegenerative disorders, but the mechanism of toxicity remains unclear. To gain insight into this neurotoxicity, this study sought to examine global gene expression changes caused by exposure to ambient ultrafine PM. Microarray analysis was performed on primary human neurons derived from fetal brain tissue after a 24h exposure to 20μg/mL of ambient ultrafine particles. We found a majority of the changes in noncoding RNAs, which are involved in epigenetic regulation of gene expression, and thereby could impact the expression of several other protein coding gene targets. Although neurons from biologically different lot numbers were used, we found a significant increase in the expression of metallothionein 1A and 1F in all samples after exposure to particulate matter as confirmed by quantitative PCR. These metallothionein 1 proteins are responsible for neuroprotection after exposure to environmental insult but prolonged induction can be toxic. Epidemiological studies have reported that in utero exposure to ultrafine PM not only leads to neurodevelopmental and behavioral abnormalities, but may also predispose the progeny to neurodegenerative disease later in life by genetic imprinting. Our results pinpoint some of the PM-induced genetic changes that may underlie these findings.

Metallothionein ameliorates burn sepsis partly via activation of Akt signaling pathway in mice: a randomized animal study

Introduction

Metallothioneins (MTs) are a family of cysteine-rich and low molecular-weight proteins that can regulate metal metabolism and act as antioxidants. Recent studies showed that MTs played a protective role in excessive inflammation and sepsis. However, the role of MTs in burn sepsis remains unclear. This study is designed to investigate the role of MTs in burn sepsis in an experimental mouse model.

Methods

MT-I/II knockout (−/−) mice on a C57BL/6 background and their wild-type (WT) littermates were randomly divided into sham burn, burn, burn sepsis, Zn treated and Zn-MT-2 treated groups. Levels of inflammatory cytokines were measured by enzyme-linked immunosorbent assay (ELISA). Myeloperoxidase (MPO) activity was detected by spectrophotometry. In in vitro study, exogenous MT was added to macrophages that stimulated with serum from burn sepsis mice with or without Akt inhibitor LY294002. The IL-1 β and IL-6 mRNA expression were detected by quantitative real-time polymerase chain reaction. The levels of Akt expression were determined by western blot.

Results

Burn sepsis induced significantly elevated levels of inflammatory cytokines in serum and increased inflammatory infiltration in the liver and lung. These effects were more prominent in MT (−/−) mice than in WT mice. Furthermore, exogenous MT-2 inhibited these elevated inflammatory response in both WT and MT (−/−) mice. MT-2 up-regulated Akt phosphorylation and abrogated the increase of IL-1β and IL-6 mRNA expression from macrophages that stimulated with burn sepsis serum. These effects of MT-2 were abolished in the presence of LY294002.

Conclusion

MT-2 ameliorates burn sepsis by attenuating inflammatory response and diminishing inflammatory organ damage, which is at least partly mediated by activation of Akt signaling pathway.

Copper at the Fungal Pathogen-Host Axis

Fungal infections are responsible for millions of human deaths annually. Copper, an essential but toxic trace element, plays an important role at the host-pathogen axis during infection. In this review, we describe how the host uses either Cu compartmentalization within innate immune cells or Cu sequestration in other infected host niches such as in the brain to combat fungal infections. We explore Cu toxicity mechanisms and the Cu homeostasis machinery that fungal pathogens bring into play to succeed in establishing an infection. Finally, we address recent approaches that manipulate Cu-dependent processes at the host-pathogen axis for antifungal drug development.

Two metallothionein genes in Oxya chinensis: molecular characteristics, expression patterns and roles in heavy metal stress

Metallothioneins (MTs) are small, cysteine-rich, heavy metal-binding proteins involved in metal homeostasis and detoxification in living organisms. In the present study, we cloned two MT genes (OcMT1 and OcMT2) from Oxya chinensis, analyzed the expression patterns of the OcMT transcripts in different tissues and at varying developmental stages using real-time quantitative PCR (RT-qPCR), evaluated the functions of these two MTs using RNAi and recombinant proteins in an E. coli expression system. The full-length cDNAs of OcMT1 and OcMT2 encoded 40 and 64 amino acid residues, respectively. We found Cys-Cys, Cys-X-Cys and Cys-X-Y-Z-Cys motifs in OcMT1 and OcMT2. These motifs might serve as primary chelating sites, as in other organisms. These characteristics suggest that OcMT1 and OcMT2 may be involved in heavy metal detoxification by capturing the metals. Two OcMT were expressed at all developmental stages, and the highest levels were found in the eggs. Both transcripts were expressed in all eleven tissues examined, with the highest levels observed in the brain and optic lobes, followed by the fat body. The expression of OcMT2 was also relatively high in the ovaries. The functions of OcMT1 and OcMT2 were explored using RNA interference (RNAi) and different concentrations and treatment times for the three heavy metals. Our results indicated that mortality increased significantly from 8.5% to 16.7%, and this increase was both time- and dose-dependent. To evaluate the abilities of these two MT proteins to confer heavy metal tolerance to E. coli, the bacterial cells were transformed with pET-28a plasmids containing the OcMT genes. The optical densities of both the MT-expressing and control cells decreased with increasing concentrations of CdCl2. Nevertheless, the survival rates of the MT-overexpressing cells were higher than those of the controls. Our results suggest that these two genes play important roles in heavy metal detoxification in O. chinensis.

Metallothionein and stress combine to affect multiple organ systems

Metallothioneins (MTs) are a family of low molecular weight, cysteine-rich, metal-binding proteins that have a wide range of functions in cellular homeostasis and immunity. MTs can be induced by a variety of conditions including metals, glucocorticoids, endotoxin, acute phase cytokines, stress, and irradiation. In addition to their important immunomodulatory functions, MTs can protect essential cellular compartments from toxicants, serve as a reservoir of essential heavy metals, and regulate cellular redox potential. Many of the roles of MTs in the neuroinflammation, intestinal inflammation, and stress response have been investigated and were the subject of a session at the 6th International Congress on Stress Proteins in Biology and Medicine in Sheffield, UK. Like the rest of the cell stress response, there are therapeutic opportunities that arise from an understanding of MTs, and these proteins also provide potential insights into the world of the heat shock protein.

Glia and zinc in ageing and Alzheimer's disease: a mechanism for cognitive decline?

Normal ageing is characterized by cognitive decline across a range of neurological functions, which are further impaired in Alzheimer’s disease (AD). Recently, alterations in zinc (Zn) concentrations, particularly at the synapse, have emerged as a potential mechanism underlying the cognitive changes that occur in both ageing and AD. Zn is now accepted as a potent neuromodulator, affecting a variety of signaling pathways at the synapse that are critical to normal cognition. While the focus has principally been on the neuron: Zn interaction, there is a growing literature suggesting that glia may also play a modulatory role in maintaining both Zn ion homeostasis and the normal function of the synapse. Indeed, zinc transporters (ZnT’s) have been demonstrated in glial cells where Zn has also been shown to have a role in signaling. Furthermore, there is increasing evidence that the pathogenesis of AD critically involves glial cells (such as astrocytes), which have been reported to contribute to amyloid-beta (Aβ) neurotoxicity. This review discusses the current evidence supporting a complex interplay of glia, Zn dyshomeostasis and synaptic function in ageing and AD.

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.

The role of intracellular zinc release in aging, oxidative stress, and Alzheimer's disease

Brain aging is marked by structural, chemical, and genetic changes leading to cognitive decline and impaired neural functioning. Further, aging itself is also a risk factor for a number of neurodegenerative disorders, most notably Alzheimer’s disease (AD). Many of the pathological changes associated with aging and aging-related disorders have been attributed in part to increased and unregulated production of reactive oxygen species (ROS) in the brain. ROS are produced as a physiological byproduct of various cellular processes, and are normally detoxified by enzymes and antioxidants to help maintain neuronal homeostasis. However, cellular injury can cause excessive ROS production, triggering a state of oxidative stress that can lead to neuronal cell death. ROS and intracellular zinc are intimately related, as ROS production can lead to oxidation of proteins that normally bind the metal, thereby causing the liberation of zinc in cytoplasmic compartments. Similarly, not only can zinc impair mitochondrial function, leading to excess ROS production, but it can also activate a variety of extra-mitochondrial ROS-generating signaling cascades. As such, numerous accounts of oxidative neuronal injury by ROS-producing sources appear to also require zinc. We suggest that zinc deregulation is a common, perhaps ubiquitous component of injurious oxidative processes in neurons. This review summarizes current findings on zinc dyshomeostasis-driven signaling cascades in oxidative stress and age-related neurodegeneration, with a focus on AD, in order to highlight the critical role of the intracellular liberation of the metal during oxidative neuronal injury.

Quantitation of human metallothionein isoforms: a family of small, highly conserved, cysteine-rich proteins

Human metallothioneins (MTs) are important regulators of metal homeostasis and protectors against oxidative damage. Their altered mRNA expression has been correlated with metal toxicity and a variety of cancers. Current immunodetection methods lack the specificity to distinguish all 12 human isoforms. Each, however, can be distinguished by the mass of its acetylated, cysteine-rich, hydrophilic N-terminal tryptic peptides. These properties were exploited to develop a bottom-up MALDI-TOF/TOF-MS-based method for their simultaneous quantitation. Key features included enrichment of N-terminal acetylated peptides by strong cation exchange chromatography, optimization of C18 reversed-phase chromatography, and control of methionine oxidation. Combinations of nine isoforms were identified in seven cell lines and two tissues. Relative quantitation was accomplished by comparing peak intensities of peptides generated from pooled cytosolic proteins alkylated with ¹⁴N- or ¹⁵N-iodoacetamide. Absolute quantitation was achieved using ¹⁵N-iodoacetamide-labeled synthetic peptides as internal standards. The method was applied to the cadmium induction of MTs in human kidney HK-2 epithelial cells expressing recombinant MT-3. Seven isoforms were detected with abundances spanning almost 2 orders of magnitude and inductions up to 12-fold. The protein-to-mRNA ratio for MT-1E was one-tenth that of other MTs, suggesting isoform-specific differences in protein expression efficiency. Differential expression of MT-1G1 and MT-1G2 suggested tissue- and cell-specific alternative splicing for the MT-1G isoform. Protein expression of MT isoforms was also evaluated in human breast epithelial cancer cell lines. Estrogen-receptor-positive cell lines expressed only MT-2 and MT-1X, whereas estrogen-receptor-negative cell lines additionally expressed MT-1E. The combined expression of MT isoforms was 38-fold greater in estrogen-receptor-negative cell lines than in estrogen-receptor-positive cells. These findings demonstrate that individual human MT isoforms can be accurately quantified in cells and tissues at the protein level, complementing and expanding mRNA measurement as a means for evaluating MTs as potential biomarkers for cancers or heavy metal toxicity.

Challenging conventional wisdom: single domain metallothioneins

Metallation studies of human metallothioneins support the role of single metal-binding-domains as commonplace with the typical two-domain-cluster structure as exceptional.

Hepatic expression of metallothionein I/II, glycoprotein 96, IL-6, and TGF- β in rat strains with different susceptibilities to experimental autoimmune encephalomyelitis

In a search of peripheral factors that could be responsible for the discrepancy in susceptibility to EAE in Albino Oxford (AO) and Dark Agouti (DA) rats, we estimated the expression of metallothioneins I/II (MT), heat shock protein-gp96, interleukin (IL)-6, and transforming growth factor (TGF)-β in the livers of these animals. Rats were immunized with bovine brain homogenate (BBH) emulsified in complete Freund adjuvant (CFA) or only with CFA. Western blot and immunohistochemical analyses were done on day 12 after the immunization, as well as in intact rats. The data have shown that during the first attack of EAE only the EAE prone-DA rats markedly upregulated the hepatic MTs, gp96, IL-6, and TGF-β. In contrast, AO rats had a significantly higher expression of MT I/II, IL-6, and TGF-β in intact liver (P < 0,001), suggesting that the greater constitutive expression of these proteins contributed to the resistance of EAE. Besides, since previously we found that AO rats reacted on immunization by an early upregulation of TGF-β on several hepatic structures (vascular endothelium, Kupffer cells, and hepatocytes), the data suggest that the specific hepatic microenvironment might contribute also to the faster recovery of these rats from EAE.

Potential roles of zinc in the pathophysiology and treatment of major depressive disorder

Incomplete response to monoaminergic antidepressants in major depressive disorder (MDD), and the phenomenon of neuroprogression, suggests a need for additional pathophysiological markers and pharmacological targets. Neuronal zinc is concentrated exclusively within glutamatergic neurons, acting as an allosteric modulator of the N-methyl D-aspartate and other receptors that regulate excitatory neurotransmission and neuroplasticity. Zinc-containing neurons form extensive associational circuitry throughout the cortex, amygdala and hippocampus, which subserve mood regulation and cognitive functions. In animal models of depression, zinc is reduced in these circuits, zinc treatment has antidepressant-like effects and dietary zinc insufficiency induces depressive behaviors. Clinically, serum zinc is lower in MDD, which may constitute a state-marker of illness and a risk factor for treatment-resistance. Marginal zinc deficiency in MDD may relate to multiple putative mechanisms underlying core symptomatology and neuroprogression (e.g. immune dysfunction, monoamine metabolism, stress response dysregulation, oxidative/nitrosative stress, neurotrophic deficits, transcriptional/epigenetic regulation of neural networks). Initial randomized trials suggest a benefit of zinc supplementation. In summary, molecular and animal behavioral data support the clinical significance of zinc in the setting of MDD.

The relevance of metals in the pathophysiology of neurodegeneration, pathological considerations

Neurodegenerative disorders are featured by a variety of pathological conditions that share similar critical processes, such as oxidative stress, free radical activity, proteinaceous aggregations, mitochondrial dysfunctions, and energy failure. They are mediated or triggered by an imbalance of metal ions leading to changes of critical biological systems and initiating a cascade of events finally leading to neurodegeneration and cell death. Their causes are multifactorial, and although the source of the shift in oxidative homeostasis is still unclear, current evidence points to changes in the balance of redox transition metals, especially iron, copper, and other trace metals. They are present at elevated levels in Alzheimer disease, Parkinson disease, multisystem atrophy, etc., while in other neurodegenerative disorders, copper, zinc, aluminum, and manganese are involved. This chapter will review the recent advances of the role of metals in the pathogenesis and pathophysiology of major neurodegenerative diseases and discuss the use of chelating agents as potential therapies for metal-related disorders.

Metallothioneins I/II expression in rat strains with genetically different susceptibility to experimental autoimmune encephalomyelitis

OBJECTIVES

Compared to the Dark Agouti (DA), the Albino Oxford (AO) rat strain exhibits lower susceptibility to the induction of experimental autoimmune encephalomyelitis (EAE). Here, we investigated the potential contribution of the heavy metal-binding proteins metallothioneins (MTs) I/II to these effects.

METHODS

Rats were immunized with bovine brain homogenate emulsified in complete Freund's adjuvant or only with complete Freund's adjuvant. The expression patterns of MTs mRNA and proteins and tissue concentrations of Zn2+ and Cu2+ were estimated in the brain and in the liver on days 7 and 12 after immunization, by real-time PCR, immunohistochemistry and inductively coupled plasma spectrometry, respectively. Additionally, the hepatic transforming growth factor beta and nuclear factor kappa B immunoreactivities were tested.

RESULTS

Clinical signs of EAE were not induced in AO rats, but they upregulated the expression of MT I/II proteins in the brain (hippocampus and cerebellum) and in the liver, similarly as DA rats. The transcriptional activation of MT-I occurred, however, only in DA rats, which accumulated also more zinc in the brain and in the liver. In contrast, intact AO rats had greater hepatic MT-I mRNA immunoreactivity and more Cu2+ in the hippocampus. Besides, in immunized AO rats a high upregulation of transforming growth factor beta and nuclear factor kappa B immunoreactivities was found in several hepatic structures (vascular endothelium, Kupffer cells and hepatocytes).

CONCLUSIONS

Our data show that AO and DA rats differ in constitutive and inductive MT-I gene expression in the brain and in the liver, as well as in the hepatic cytokine profile, suggesting that these mechanisms may contribute to the discrepancy in the susceptibility to EAE.

Characterization of the role of metallothionein-3 in an animal model of Alzheimer's disease

Among the dementias, Alzheimer's disease (AD) is the most commonly diagnosed, but there are still no effective drugs available for its treatment. It has been suggested that metallothionein-3 (MT-3) could be somehow involved in the etiology of AD, and in fact very promising results have been found in in vitro studies, but the role of MT-3 in vivo needs further analysis. In this study, we analyzed the role of MT-3 in a mouse model of AD, Tg2576 mice, which overexpress human Amyloid Precursor Protein (hAPP) with the Swedish mutation. MT-3 deficiency partially rescued the APP-induced mortality of females, and mildly affected APP-induced changes in behavior assessed in the hole-board and plus-maze tests in a gender-dependent manner. Amyloid plaque burden and/or hAPP expression were decreased in the cortex and hippocampus of MT-3-deficient females. Interestingly, exogenously administered Zn(7)MT-3 increased soluble Aβ40 and Aβ42 and amyloid plaques and gliosis, particularly in the cortex, and changed several behavioral traits (increased deambulation and exploration and decreased anxiety). These results highlight that the control of the endogenous production and/or action of MT-3 could represent a powerful therapeutic target in AD.

Characterization of the role of the antioxidant proteins metallothioneins 1 and 2 in an animal model of Alzheimer's disease

Alzheimer's disease (AD) is by far the most commonly diagnosed dementia, and despite multiple efforts, there are still no effective drugs available for its treatment. One strategy that deserves to be pursued is to alter the expression and/or physiological action of endogenous proteins instead of administering exogenous factors. In this study, we intend to characterize the roles of the antioxidant, anti-inflammatory, and heavy-metal binding proteins, metallothionein-1 + 2 (MT1 + 2), in a mouse model of Alzheimer's disease, Tg2576 mice. Contrary to expectations, MT1 + 2-deficiency rescued partially the human amyloid precursor protein-induced changes in mortality and body weight in a gender-dependent manner. On the other hand, amyloid plaque burden was decreased in the cortex and hippocampus in both sexes, while the amyloid cascade, neuroinflammation, and behavior were affected in the absence of MT1 + 2 in a complex manner. These results highlight that the control of the endogenous production and/or action of MT1 + 2 could represent a powerful therapeutic target in AD.

Amyloid neurotoxicity is attenuated by metallothionein: dual mechanisms at work

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive loss of memory and cognition. One of the hallmarks of AD is the accumulation of beta-amyloid (Aβ). Although endoplasmic reticulum stress, mitochondrial dysfunction, and oxidative stress have been implicated in Aβ toxicity, the molecular mechanism(s) of Aβ-induced neurotoxicity are not fully understood. In this study, we present evidence that the glia-derived stress protein metallothionein (MT) attenuates Aβ-induced neurotoxicity by unique mechanisms. MT expression was increased in brain astrocytes of a NSE-APPsw transgenic mouse model of AD. Astrocyte-derived MT protected N2a neuroblastoma cells and primary cortical neurons against Aβ toxicity with concurrent reduction of reactive oxygen species levels. MT reversed Aβ-induced down-regulation of Bcl-2 and survival signaling in neuroblastoma cells. Moreover, MT inhibited Aβ-induced proinflammatory cytokine production from microglia. The neurotoxicity of Aβ-stimulated microglia was significantly attenuated by MT-I. The results indicate that MT released from reactive astrocytes may antagonize Aβ neurotoxicity by direct inhibition of Aβ neurotoxicity and indirect suppression of neurotoxic microglial activation. These findings broaden the understanding of neurotoxic mechanisms of Aβ and the crosstalk between Aβ and MT in AD.

Environmental factors in autism

Autism is a neurodevelopmental disorders characterized by impairments in communication and social behavior, and by repetitive behaviors. Although genetic factors might be largely responsible for the occurrence of autism they cannot fully account for all cases and it is likely that in addition to a certain combination of autism-related genes, specific environmental factors might act as risk factors triggering the development of autism. Thus, the role of environmental factors in autism is an important area of research and recent data will be discussed in this review. Interestingly, the results show that many environmental risk factors are interrelated and their identification and comparison might unveil a common scheme of alterations on a contextual as well as molecular level. For example, both, disruption in the immune system and in zinc homeostasis may affect synaptic transmission in autism. Thus, here, a model is proposed that interconnects the most important and scientifically recognized environmental factors. Moreover, similarities in how these risk factors impact synapse function are discussed and a possible influence on an already well described genetic pathway leading to the development of autism via zinc homeostasis is proposed.