Significance of metallothioneins in aging brain

Transcriptomic and morphological maturation of human astrocytes in cerebral organoids

Cerebral organoids (CerOrgs) derived from human induced pluripotent stem cells (iPSCs) are a valuable tool to study human astrocytes and their interaction with neurons and microglia. The timeline of astrocyte development and maturation in this model is currently unknown and this limits the value and applicability of the model. Therefore, we generated CerOrgs from three healthy individuals and assessed astrocyte maturation after 5, 11, 19, and 37 weeks in culture. At these four time points, the astrocyte lineage was isolated based on the expression of integrin subunit alpha 6 (ITGA6). Based on the transcriptome of the isolated ITGA6-positive cells, astrocyte development started between 5 and 11 weeks in culture and astrocyte maturation commenced after 11 weeks in culture. After 19 weeks in culture, the ITGA6-positive astrocytes had the highest expression of human mature astrocyte genes, and the predicted functional properties were related to brain homeostasis. After 37 weeks in culture, a subpopulation of ITGA6-negative astrocytes appeared, highlighting the heterogeneity within the astrocytes. The morphology shifted from an elongated progenitor-like morphology to the typical bushy astrocyte morphology. Based on the morphological properties, predicted functional properties, and the similarities with the human mature astrocyte transcriptome, we concluded that ITGA6-positive astrocytes have developed optimally in 19-week-old CerOrgs.

The Role of Oxidative Stress in Manganese Neurotoxicity: A Literature Review Focused on Contributions Made by Professor Michael Aschner

This literature review focuses on the evidence implicating oxidative stress in the pathogenesis of manganese neurotoxicity. This review is not intended to be a systematic review of the relevant toxicologic literature. Instead, in keeping with the spirit of this special journal issue, this review highlights contributions made by Professor Michael Aschner's laboratory in this field of study. Over the past two decades, his laboratory has made significant contributions to our scientific understanding of cellular responses that occur both in vitro and in vivo following manganese exposure. These studies have identified molecular targets of manganese toxicity and their respective roles in mitochondrial dysfunction, inflammation, and cytotoxicity. Other studies have focused on the critical role astrocytes play in manganese neurotoxicity. Recent studies from his laboratory have used C. elegans to discover new facets of manganese-induced neurotoxicity. Collectively, his body of work has dramatically advanced the field and presents broader implications beyond metal toxicology.

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

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

TRPM2 Channel Inhibition Attenuates Amyloid β42-Induced Apoptosis and Oxidative Stress in the Hippocampus of Mice

Alzheimer's disease (AD) is characterized by the increase of hippocampal Ca²⁺ influx-induced apoptosis and mitochondrial oxidative stress (OS). The OS is a stimulator of TRPM2, although N-(p-amylcinnamoyl)anthranilic acid (ACA), 2-aminoethyl diphenylborinate (2/APB), and glutathione (GSH) are non-specific antagonists of TRPM2. In the present study, we investigated the protective roles of GSH and TRPM2 antagonist treatments on the amyloid β42 peptide (Aβ)-caused oxidative neurotoxicity and apoptosis in the hippocampus of mice with AD model. After the isolation of hippocampal neurons from the newborn mice, they were divided into five incubation groups as follows: control, ACA, Aβ, Aβ+ACA, and Aβ+GSH. The levels of apoptosis, hippocampus death, cytosolic ROS, cytosolic Zn²⁺, mitochondrial ROS, caspase-3, caspase-9, lipid peroxidation, and cytosolic Ca²⁺ were increased in the primary hippocampus cultures by treatments of Aβ, although their levels were decreased in the neurons by the treatments of GSH, PARP-1 inhibitors (PJ34 and DPQ), and TRPM2 blockers (ACA and 2/APB). The Aβ-induced decreases of cell viability, cytosolic GSH, reduced GSH, and GSH peroxidase levels were also increased in the groups of Aβ+ACA and Aβ+GSH by the treatments of ACA and GSH. However, the Aβ-caused changes were not observed in the hippocampus of TRPM2-knockout mice. In conclusion, the present data demonstrate that maintaining the activation of TRPM2 is not only important for the quenching OS and neurotoxicity in the hippocampal neurons of mice with experimental AD but also equally critical to the modulation of Aβ-induced apoptosis. The possible positive effects of GSH and TRPM2 antagonist treatments on the amyloid-beta (Aβ)-induced oxidative toxicity in the hippocampus of mice. The ADP-ribose (ADPR) is produced via the stimulation of PARP-1 in the nucleus of neurons. The NUT9 in the C terminus of TRPM2 channel acts as a key role for the activation of TRPM2. The antagonists of TRPM2 are glutathione (GSH), ACA, and 2/APB in the hippocampus. The Aβ incubation-mediated TRPM2 stimulation increases the concentration of cytosolic-free Ca²⁺ and Zn²⁺ in the hippocampus. In turn, the increased concentration causes the increase of mitochondrial membrane potential (ΔΨm), which causes the excessive generations of mitochondria ROS and the decrease of cytosolic GSH and GSH peroxidase (GSH-Px). The ROS production and GSH depletion are two main causes in the neurobiology of Alzheimer's disease. However, the effect of Aβ was not shown in the hippocampus of TRPM2-knockout mice. The Aβ and TRPM2 stimulation-caused overload Ca²⁺ entry cause apoptosis and cell death via the activations of caspase-3 (Casp/3) and caspase-9 (Casp/9) in the hippocampus. The actions of Aβ-induced oxidative toxicity were modulated in the primary hippocampus by the incubations of ACA, GSH, 2/APB, and PARP-1 inhibitors (PJ34 and DPQ). (↑) Increase. (↓) Decrease.

Molecular Genetics and Cytotoxic Responses to Titanium Diboride and Zinc Borate Nanoparticles on Cultured Human Primary Alveolar Epithelial Cells

Titanium diboride (TiB₂) and zinc borate (Zn₃BO₆) have been utilized in wide spectrum industrial areas because of their favorable properties such as a high melting point, good wear resistance, high hardness and thermal conductivity. On the other hand, the biomedical potentials of TiB₂ and Zn₃BO₆ are still unknown because there is no comprehensive analysis that uncovers their biocompatibility features. Thus, the toxicogenomic properties of TiB₂ and Zn₃BO₆ nanoparticles (NPs) were investigated on human primary alveolar epithelial cell cultures (HPAEpiC) by using different cell viability assays and microarray analyses. Protein-Protein Interaction Networks Functional Enrichment Analysis (STRING) was used to associate differentially expressed gene probes. According to the results, up to 10 mg/L concentration of TiB₂ and Zn₃BO₆ NPs application did not stimulate a cytotoxic effect on the HPAEpiC cell cultures. Microarray analysis revealed that TiB₂ NPs exposure enhances cellular adhesion molecules, proteases and carrier protein expression. Furthermore, Zn₃BO₆ NPs caused differential gene expressions in the cell cycle, cell division and extracellular matrix regulators. Finally, STRING analyses put forth that inflammation, cell regeneration and tissue repair-related gene interactions were affected by TiB₂ NPs application. Zn₃BO₆ NPs exposure significantly altered inflammation, lipid metabolism and infection response activator-related gene interactions. These investigations illustrated that TiB₂ and Zn₃BO₆ NPs exposure may affect different aspects of cellular machineries such as immunogenic responses, tissue regeneration and cell survival. Thus, these types of cellular mechanisms should be taken into account before the use of the related NPs in further biomedical applications.

Diverse human astrocyte and microglial transcriptional responses to Alzheimer's pathology

To better define roles that astrocytes and microglia play in Alzheimer’s disease (AD), we used single-nuclei RNA-sequencing to comprehensively characterise transcriptomes in astrocyte and microglia nuclei selectively enriched during isolation post-mortem from neuropathologically defined AD and control brains with a range of amyloid-beta and phospho-tau (pTau) pathology. Significant differences in glial gene expression (including AD risk genes expressed in both the astrocytes [CLU, MEF2C, IQCK] and microglia [APOE, MS4A6A, PILRA]) were correlated with tissue amyloid or pTau expression. The differentially expressed genes were distinct between with the two cell types and pathologies, although common (but cell-type specific) gene sets were enriched with both pathologies in each cell type. Astrocytes showed enrichment for proteostatic, inflammatory and metal ion homeostasis pathways. Pathways for phagocytosis, inflammation and proteostasis were enriched in microglia and perivascular macrophages with greater tissue amyloid, but IL1-related pathway enrichment was found specifically in association with pTau. We also found distinguishable sub-clusters in the astrocytes and microglia characterised by transcriptional signatures related to either homeostatic functions or disease pathology. Gene co-expression analyses revealed potential functional associations of soluble biomarkers of AD in astrocytes (CLU) and microglia (GPNMB). Our work highlights responses of both astrocytes and microglia for pathological protein clearance and inflammation, as well as glial transcriptional diversity in AD.

Metallothioneins and Megalin Expression Profiling in Premalignant and Malignant Oral Squamous Epithelial Lesions

This study aimed to assess the relationship and possible interactions between metallothioneins (MTs) and megalin (LRP-2) in different grades of oral squamous cell carcinoma (OSCC) and premalignant lesions of the oral mucosa (oral leukoplakia and oral lichen planus). The study included archived samples of 114 patients and control subjects. Protein expression was examined by immunohistochemistry and immunofluorescence, and staining quantification was performed by ImageJ software. Protein interaction in cancer tissue was tested and visualized by proximity ligation assay. Mann-Whitney and Kruskal-Wallis tests were used to determine the significance of differences between each group, whereas Pearson correlation coefficient was performed to test correlation. Expression of both proteins differed significantly between each group showing the same pattern of gradual increasing from oral lichen planus to poorly differentiated OSCC. Moreover, MTs and megalin were found to co-express and interact in cancer tissue, and their expression positively correlated within the overall study group. Findings of prominent nuclear and chromosomal megalin expression suggest that it undergoes regulated intramembrane proteolysis upon MTs binding, indicating its ability to directly affect gene expression and cellular division in cancer tissue. The data obtained point to the onco-driving potential of MTs-megalin interaction.

The MT1G Gene in LUHMES Neurons Is a Sensitive Biomarker of Neurotoxicity

Identification of toxicants that underlie neurological diseases is a neglected area awaiting a valid strategy to identify such toxicants. We sought biomarkers that respond to known neurotoxicants in LUHMES immortalized neurons and evaluated these biomarkers for use in screening libraries of environmental toxicants. LUHMES immortalized human dopaminergic neurons were surveyed by RNA sequencing following challenge with parkinsonian toxicants rotenone, 6-hydroxydopamine, MPP+, and ziram (zinc dimethyldithiocarbamate; Zn²⁺DDC₂), as well as additional toxicants paraquat, MS275, and methylmercury. The metallothionein gene MT1G was the most dynamic gene expression response to all seven toxicants. Multiple toxicants also increased transcripts for SLC30A1 and SLC30A2 zinc secretion transporters, the SLC7A11 xCT cystine/glutamate antiporter important for glutathione synthesis, DNA damage inducible transcript 3 (DDIT3), and secreted growth factors FIBIN and CXCL12, whereas several toxicants decreased expression of the apelin growth factor (APLN). These biomarker genes revealed stress responses to many toxicants at sub-cytotoxic concentrations. Since several of these biomarker genes and prior neurological disease studies implicated disruption of metal distribution, we tested metal chelator thiram (dimethyldithiocarbamate, DDC), ziram, and several other metals and metal chelates for cytotoxicity and induction of MT1G expression. Metals and chelators that caused dynamic increases in MT1G expression also caused cytotoxicity, except Ni²⁺DDC₂ induced MT1G at 5 μM, but lacked cytotoxicity up to 100 μM. These results bolster prior work suggesting that neurons are characteristically sensitive to depletion of glutathione or to disruption of cellular metal distribution and provide biomarkers to search for such neurotoxicants in chemical libraries.

Exploring the brain tissue proteome of TgCRND8 Alzheimer's Disease model mice under B vitamin deficient diet induced hyperhomocysteinemia by LC-MS top-down platform

The multifactorial nature of Late Onset Alzheimer's Disease (LOAD), the AD form of major relevance on epidemiological and social aspects, has driven the original investigation by LC-MS and top-down proteomics approach of the protein repertoire of the brain tissue of TgCRND8 model mice fed with a diet deficient in B vitamins. The analysis of the acid-soluble fraction of brain tissue homogenates identified a list of proteins and peptides, proteoforms and PTMs. In order to disclose possible modulations, their relative quantification in wild type and AD model mice under both B vitamin deficient and control diets was performed. The levels of metallothionein III, guanine nucleotide-binding protein G(I)/G(S)/G(O) subunit gamma-2 and brain acid soluble protein 1 showed statistically significant alterations depending on genotype, diet or both effects, respectively. Particularly, metallothionein III exhibited increased levels in TgCRND8 mice under B vitamin deficient diet with respect to wild type mice under both diets. Brain acid soluble protein 1 showed the opposite, revealing decreased levels in all diet groups of AD model mice with respect to wild type mice in control diet. Lower levels of brain acid soluble protein 1 were also observed in wild type mice under deficiency of B vitamins. These results, besides contributing to increase the knowledge of AD at molecular level, give new suggestions for deeply investigating metallothionein III and brain acid soluble protein 1 in AD.

Molecular Mechanisms of Zinc as a Pro-Antioxidant Mediator: Clinical Therapeutic Implications

The essentiality of zinc as a trace mineral in human health has been recognized for over five decades. Zinc deficiency, caused by diet, genetic defects, or diseases, can cause growth retardation, delayed sexual maturation, depressed immune response, and abnormal cognitive functions in humans. Zinc supplementation in zinc-deficient individuals can overcome or attenuate these abnormalities, suggesting zinc is an essential micro-nutrient in the body. A large number of in vitro and in vivo experimental studies indicate that zinc deficiency also causes apoptosis, cellular dysfunction, deoxyribonucleic acid (DNA) damage, and depressed immune response. Oxidative stress, due to the imbalance of reactive oxygen species (ROS) production and detoxification in the anti-oxidant defense system of the body, along with subsequent chronic inflammation, is believed to be associated with many chronic degenerative diseases such as diabetes, heart diseases, cancers, alcohol-related disease, macular degenerative disease, and neuro-pathogenesis. A large number of experimental studies including cell culture, animal, and human clinical studies have provided supportive evidence showing that zinc acts as an anti-oxidative stress agent by inhibition of oxidation of macro-molecules such as (DNA)/ribonucleic acid (RNA) and proteins as well as inhibition of inflammatory response, eventually resulting in the down-regulation of (ROS) production and the improvement of human health. In this article, we will discuss the molecular mechanisms of zinc as an anti-oxidative stress agent or mediator in the body. We will also discuss the applications of zinc supplementation as an anti-oxidative stress agent or mediator in human health and disease.

In Vitro Cytotoxicity of Zinc Fructoborate, a Novel Zinc-Boron Active Natural Complex

In recent years, the role of zinc in biological systems has been a subject of intense research. Zinc is required for multiple metabolic processes as a structural, regulatory, or catalytic ion. The objective of this study, was to assess the toxicity profile of a newly synthesized zinc-boron molecule on cultured cells. Zinc fructoborate, at different levels of concentration, was tested for its impact on the Vero kidney cell line (ATCC® CCL-81™) using the MTT assay. The compound exhibited a low cytotoxic effect on the cell line. Thus, our study demonstrates that the zinc fructoborate could become a promising dietary supplement molecule.

The Design and Application of an Appropriate Parkinson's Disease Animal Model in Regenerative Medicine

OBJECTIVES

Aging as an inevitable and complex physiological process occurs through a progressive decrease in the potential of tissue regeneration. Given the increasing global outbreak of aging and age-related disorders, it is important to control this phenomenon. Parkinson's disease (one of the age-related neurodegenerative and progressive disorders) resulted from predominant dopaminergic neurons deficiency. Usual Parkinson's disease treatments just can lead to symptomatically relieving. Recently, cell therapy and regenerative medicine a great promise in the treatment of several types of disorders including Parkinson's disease. Herein, before starting clinical trials, preclinical studies should be performed to answer some fundamental questions about the safety and efficacy of various treatments. Additionally, developing a well-designed and approved study is required to provide an appropriate animal model with strongly reliable validation methods. Hereupon, this review will discuss about the design and application of an appropriate Parkinson's disease animal model in regenerative medicine.

EVIDENCE ACQUISITION

In order to conduct the present review, numbers of Parkinson's disease preclinical studies, as well as literatures related to the animal modeling, were considered.

RESULTS

Appropriate animal models which approved by related authorize committees should have a high similarity to humans from anatomical, physiological, behavioral, and genetic characteristics view of point.

CONCLUSION

It is concluded that animal studies before starting clinical trials have an important role in answering the crucial questions about the various treatments safety and efficacy. Therein, it is recommended that all of animal modeling stages be assessed by animal ethics and welfare guidelines and also evaluated by different validation tests. However, it is better to find some alternatives to replacement, refinement, and, reduction of animals. Nowadays, some novel technologies such as using imaging methods have been introduced.

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.

Chlorinative stress in age-related diseases: a literature review

Aging is an agglomerate of biological long-lasting processes that result being inevitable. Main actors in this scenario are both long-term inflammation and oxidative stress. It has been proved that oxidative stress induce alteration in proteins and this fact itself is critically important in the pathophysiological mechanisms leading to diseases typical of aging. Among reactive species, chlorine ones such as hypochlorous acid (HOCl) are cytotoxic oxidants produced by activated neutrophils during chronic inflammation processes. HOCl can also cause damages by reacting with biological molecules. HOCl is generated by myeloperoxidase (MPO) and augmented serum levels of MPO have been described in acute and chronic inflammatory conditions in cardiovascular patients and has been implicated in many inflammatory diseases such as atherosclerosis, neurodegenerative conditions, and some cancers. Due to these data, we decided to conduct an up-to-date review evaluating chlorinative stress effects on every age-related disease linked; potential anti-oxidant countermeasures were also assessed. Results obtained associated HOCl generation to the aging processes and confirmed its connection with diseases like neurodegenerative and cardiovascular pathologies, atherosclerosis and cancer; chlorination was mainly linked to diseases where molecular (protein) alteration constitute the major suspected cause: i.e. inflammation, tissue lesions, DNA damages, apoptosis and oxidative stress itself. According data collected, a healthy lifestyle together with some dietary suggestion and/or the administration of nutracetical antioxidant integrators could balance the effects of chlorinative stress and, in some cases, slow down or prevent the onset of age-releated diseases.

Astroglia as a cellular target for neuroprotection and treatment of neuro-psychiatric disorders

Astrocytes are key homeostatic cells of the central nervous system. They cooperate with neurons at several levels, including ion and water homeostasis, chemical signal transmission, blood flow regulation, immune and oxidative stress defense, supply of metabolites and neurogenesis. Astroglia is also important for viability and maturation of stem-cell derived neurons. Neurons critically depend on intrinsic protective and supportive properties of astrocytes. Conversely, all forms of pathogenic stimuli which disturb astrocytic functions compromise neuronal functionality and viability. Support of neuroprotective functions of astrocytes is thus an important strategy for enhancing neuronal survival and improving outcomes in disease states. In this review, we first briefly examine how astrocytic dysfunction contributes to major neurological disorders, which are traditionally associated with malfunctioning of processes residing in neurons. Possible molecular entities within astrocytes that could underpin the cause, initiation and/or progression of various disorders are outlined. In the second section, we explore opportunities enhancing neuroprotective function of astroglia. We consider targeting astrocyte-specific molecular pathways which are involved in neuroprotection or could be expected to have a therapeutic value. Examples of those are oxidative stress defense mechanisms, glutamate uptake, purinergic signaling, water and ion homeostasis, connexin gap junctions, neurotrophic factors and the Nrf2-ARE pathway. We propose that enhancing the neuroprotective capacity of astrocytes is a viable strategy for improving brain resilience and developing new therapeutic approaches.

Trace elements in loggerhead turtles (Caretta caretta) stranded in mainland Portugal: Bioaccumulation and tissue distribution

Pollution is among the most significant threats that endanger sea turtles worldwide. Waters off the Portuguese mainland are acknowledged as important feeding grounds for juvenile loggerheads. However, there is no data on trace element concentrations in marine turtles occurring in these waters. We present the first assessment of trace element concentrations in loggerhead turtles (Caretta caretta) occurring off the coast of mainland Portugal. Also, we compare our results with those from other areas and discuss parameters that may affect element concentrations. Trace element concentrations (As, Cd, Cu, Pb, Mn, Hg, Ni, Se, Zn) were determined in kidney, liver and muscle samples from 38 loggerheads stranded between 2011 and 2013. As was the only element with higher concentrations in muscle (14.78 μg g^-1 ww) than in liver or kidney. Considering non-essential elements, Cd presented the highest concentrations in kidney (34.67 μg g^-1) and liver (5.03 μg g^-1). Only a weak positive link was found between renal Cd and turtle size. Inter-elemental correlations were observed in both liver and kidney tissues. Hepatic Hg values (0.30 ± 0.03 μg g^-1) were higher than values reported in loggerheads in the Canary Islands but lower than in Mediterranean loggerheads. Cd concentrations in the present study were only exceeded by values found in turtles from the Pacific. Although many endogenous and exogenous parameters related with complex life cycle changes and wide geographic range may influence trace element accumulation, the concentrations of Cd are probably related to the importance of crustaceans in loggerhead diet in the Portuguese coast.

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.

Age-related changes of metallothionein 1/2 and metallothionein 3 expression in rat brain

Neurodegeneration is one of the main physiological consequences of aging on brain. Metallothioneins (MTs), low molecular weight, cysteine-rich proteins that bind heavy-metal ions and oxygen-free radicals, are commonly expressed in various tissues of mammals. MTs are involved in the regulation of cell proliferation and protection, and may be engaged in aging. Expression of the ubiquitous MTs (1 and 2) and the brain specific MT3 have been studied in many neurodegenerative disorders. The research results indicate that MTs may play important, although not yet fully known, roles in brain diseases; in addition, data lack the ability to identify the MT isoforms functionally involved. The aim of this study was to analyse the level of gene expression of selected MT isoforms during brain aging. By using real-time PCR analysis, we determined the MT1/2 and MT3 expression profiles in cerebral cortex and hippocampus of adolescent (2months), adult (4 and 8months), and middle-aged (16months) rats. We show that the relative abundance of all types of MT transcripts changes during aging in both hippocampus and cortex; the first effect is a generalized decrease in the content of MTs transcripts from 2- to 8-months-old rats. After passing middle age, at 16months, we observe a huge increase in MT3 transcripts in both cortical and hippocampal areas, while the MT1/2 mRNA content increases slightly, returning to the levels measured in adolescent rats. These findings demonstrate an age-related expression of the MT3 gene. A possible link between the increasing amount of MT3 in brain aging and its different metal-binding behaviour is discussed.

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.

Serotonin 1A Receptors on Astrocytes as a Potential Target for the Treatment of Parkinson's Disease

Astrocytes are the most abundant neuron-supporting glial cells in the central nervous system. The neuroprotective role of astrocytes has been demonstrated in various neurological disorders such as amyotrophic lateral sclerosis, spinal cord injury, stroke and Parkinson’s disease (PD). Astrocyte dysfunction or loss-of-astrocytes increases the susceptibility of neurons to cell death, while astrocyte transplantation in animal studies has therapeutic advantage. We reported recently that stimulation of serotonin 1A (5-HT_1A) receptors on astrocytes promoted astrocyte proliferation and upregulated antioxidative molecules to act as a neuroprotectant in parkinsonian mice. PD is a progressive neurodegenerative disease with motor symptoms such as tremor, bradykinesia, rigidity and postural instability, that are based on selective loss of nigrostriatal dopaminergic neurons, and with non-motor symptoms such as orthostatic hypotension and constipation based on peripheral neurodegeneration. Although dopaminergic therapy for managing the motor disability associated with PD is being assessed at present, the main challenge remains the development of neuroprotective or disease-modifying treatments. Therefore, it is desirable to find treatments that can reduce the progression of dopaminergic cell death. In this article, we summarize first the neuroprotective properties of astrocytes targeting certain molecules related to PD. Next, we review neuroprotective effects induced by stimulation of 5-HT_1A receptors on astrocytes. The review discusses new promising therapeutic strategies based on neuroprotection against oxidative stress and prevention of dopaminergic neurodegeneration.

Changes in intracellular copper concentration and copper-regulating gene expression after PC12 differentiation into neurons

It is suspected that some neurodegenerative diseases are a result of the disturbance of copper (Cu) homeostasis, although it remains unclear whether the disturbance of Cu homeostasis has aberrant effects on neurons. Herein, we investigated Cu metabolism specifically in neurons in terms of changes in the intracellular Cu concentration and the expression of Cu-regulating genes, such as Cu transporters and metallothioneins (MTs), before and after the differentiation of rat pheochromocytoma cells (PC12 cells) into neurons. After the differentiation, Cu and Zn imaging with fluorescent probes revealed an increase in intracellular Cu concentration. The concentrations of other essential metals, which were determined by an inductively coupled plasma mass spectrometer, were not altered. The mRNA expression of the Cu influx transporter, Ctr1, was decreased after the differentiation, and the differentiated cells acquired tolerance to Cu and cisplatin, another substrate of Ctr1. In addition, the expression of MT-3, a brain-specific isoform, was increased, contrary to the decreased expression of MT-1 and MT-2. Taken together, the differentiation of PC12 cells into neurons induced MT-3 expression, thereby resulting in intracellular Cu accumulation. The decrease in Ctr1 expression was assumed to be a response aimed at abolishing the physiological accumulation of Cu after the differentiation.

Generation and vulnerability of deep cerebellar nuclei neurons in the weaver condition along the anteroposterior and mediolateral axes

Production and death of deep cerebellar nuclei (DCN) neurons were investigated in the weaver condition at appropriate anatomical levels throughout the mediolateral (medial, intermediate and lateral) and rostrocaudal (rostral, middle and caudal) axes of three DCN-cell groups: the fastigial, the interposed and the dentate nuclei. Current results have denoted that the deficit of DCN neurons is always more important in the homozygous weaver than in the heterozygous weaver mice. No loss of neurons was found in the dentate nucleus. In the mediolateral axis, an intranuclear gradient of depletion was observed in the mutant mice; in a given deep nucleus, neurodegeneration was more prominent in the medial pars than in lateral ones. In the rostrocaudal axis, on the other hand, when each deep nucleus was studied and compared as a whole, neuron loss was higher in the fastigial nucleus than in the interposed nucleus, which, in turn, was more important than in the dentate nucleus. These data suggest that, in the weaver condition, an internuclear gradient of neurodegeneration exists. Moreover, neurons located in rostral parts of a given nucleus appear to be more vulnerable than those settled in middle parts and these, in turn, are more than the caudal ones. These results seem to indicate the presence of an intranuclear gradient of depletion. Current autoradiographic results have revealed that, in the rostrocaudal axis, deep neurons are settled in the weaver cerebellum following three neurogenetic gradients. The first of these is internuclear; if each deep nucleus is analyzed and compared as a whole, the fastigial nucleus has more late-generated neurons than the interposed nucleus, and this, in turn, has more than the dentate nucleus. The second gradient is also internuclear; if the proportion of late-born neurons is compared throughout the rostral levels from each deep nucleus, it is observed that proportions increase from the fastigial to the dentate nucleus. A similar picture emerges when the middle and caudal regions are taken into account. The third gradient is intranuclear; in a given deep nucleus, the rostral region always presents more late-produced neurons than the middle region and these, in turn, more than in the caudal level.

Localization of genes encoding metallothionein-like protein (mt2 and smtb) in the brain of zebrafish

Metallothionein (MT) is a small cysteine-rich heavy metal-binding protein involved in metal homeostasis, detoxification and free radical-scavenging. MT is ubiquitously expressed in several tissues, but its role in the central nervous system is not well understood. In this study, we identified two MT homologous genes (mt2 and smtb) in the zebrafish. Digoxigenin-in situ hybridization showed the expression of mt2 and smtb genes in the ventricular layers in the telencephalon, diencephalon, mesencephalon and rhombencephalon, most of which are cell proliferating regions in the brain of zebrafish. Cellular characteristics of MT genes expressing cells were examined by double-labelling with markers for neurons (HuC/D) and astrocytes (glial fibrillary acidic protein, GFAP and S100 protein) and cell proliferation marker (PCNA). mt2 and smtb mRNAs are expressed in neurons and not in astrocytes, and they were co-localized with PCNA. These results suggest that mt2 and smtb may play an important role in neurogenesis and neuroprotection.

Subthalamic Nucleus Deep Brain Stimulation Modulate Catecholamine Levels with Significant Relations to Clinical Outcome after Surgery in Patients with Parkinson's Disease

Aims

Although subthalamic nucleus deep brain stimulation (STN-DBS) is effective in patients with advanced Parkinson’s disease (PD), its physiological mechanisms remain unclear. Because STN-DBS is effective in patients with PD whose motor symptoms are dramatically alleviated by L-3,4-dihydroxyphenylalanine (L-DOPA) treatment, the higher preoperative catecholamine levels might be related to the better clinical outcome after surgery. We aimed to examine the correlation between the preoperative catecholamine levels and postoperative clinical outcome after subthalamic nucleus deep brain stimulation. The effectiveness of STN-DBS in the patient who responded well to dopaminergic medication suggest the causal link between the dopaminergic system and STN-DBS. We also examined how catecholamine levels were modulated after subthalamic stimulation.

Methods

In total 25 patients with PD were enrolled (Mean age 66.2 ± 6.7 years, mean disease duration 11.6 ± 3.7 years). Mean levodopa equivalent doses were 1032 ± 34.6 mg before surgery. Cerebrospinal fluid and plasma catecholamine levels were measured an hour after oral administration of antiparkinsonian drugs before surgery. The mean Unified Parkinson’s Disease Rating Scale scores (UPDRS) and the Parkinson’s disease Questionnaire-39 (PDQ-39) were obtained before and after surgery. Of the 25 patients, postoperative cerebrospinal fluid and plasma were collected an hour after oral administration of antiparkinsonian drugs during on stimulation at follow up in 11 patients.

Results

Mean levodopa equivalent doses significantly decreased after surgery with improvement in motor functions and quality of life. The preoperative catecholamine levels had basically negative correlations with postoperative motor scores and quality of life, suggesting that higher preoperative catecholamine levels were related to better outcome after STN-DBS. The preoperative plasma levels of L-DOPA had significantly negative correlations with postoperative UPDRS- III score in off phase three months after STN-DBS. The preoperative cerebrospinal fluid (CSF) 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxytryptamine (5-HT) levels had significantly negative correlations with postoperative UPDRS- III score in off phase one year after STN-DBS and the preoperative CSF homovanilic acid (HVA) levels had significant negative correlations with postoperative UPDRS- III score in on phase three months after STN-DBS. In PDQ-39 SI (summary index), preoperative plasma dopamine (DA) level had significantly negative correlations with postoperative PDQ-39 SI one year after STN-DBS suggesting that higher preoperative plasma DA level resulted in better quality of life (QOL) one year after STN-DBS. The stepwise multiple linear regression study revealed that higher preoperative plasma HVA levels had negative influence on the postoperative motor symptoms (i.e., increase in the score of UPDRS), whereas higher preoperative CSF L-DOPA levels had positive influence on the postoperative motor symptoms and QOL (decrease in the score of UPDRS and PDQ-39 SI) The catecholamine levels were not significantly reduced postoperatively in 11 patients despite the significant reduction in levodopa equivalent doses. Unexpectedly, CSF HVA levels significantly increased from 0.00089±0.0003 ng/μl to 0.002±0.0008 ng/μl after STN-DBS.

Conclusion

The preoperative catecholamine levels might affect the postoperative motor symptoms and quality of life. The catecholamine levels were not significantly reduced postoperatively despite the significant reduction in levodopa equivalent doses.

Identification and expression of an atypical isoform of metallothionein in the African clawed frog Xenopus laevis

Exploiting the annotation of the western clawed frog Silurana tropicalis genome, we identified a new metallothionein (MT) gene, exhibiting all the features to be considered an active gene, but with an atypical coding region, showing only 17 cysteine residues instead of the canonical 20 cysteines of vertebrate metallothioneins and two anomalous cysteine triplets. However, the presence of a gene in the genome does not ensure its effective expression. By using conventional and Real-Time PCR analyses, we demonstrated that this atypical MT is constitutively expressed throughout the life cycle of the African clawed frog Xenopus laevis; moreover, this gene is highly expressed in the adult liver, the major site of MT expression and synthesis in vertebrates. To our knowledge, the X. laevis MT described in this paper is the first sequence of a vertebrate MT showing only 17 cysteine residues, arranged in two Cys-Cys-Cys motifs. Phylogenetic analyses also demonstrated that the atypical X. laevis MT merges in the anuran clade, but is the most derived sequence among tetrapods MTs. Finally, Tajima's Relative Rate Test suggested a different evolutionary rate between the canonical X. laevis MT and this novel isoform.

Zinc: indications in brain disorders

Zinc is the authoritative metal which is present in our body, and reactive zinc metal is crucial for neuronal signaling and is largely distributed within presynaptic vesicles. Zinc also plays an important role in synaptic function. At cellular level, zinc is a modulator of synaptic activity and neuronal plasticity in both development and adulthood. Different importers and transporters are involved in zinc homeostasis. ZnT-3 is a main transporter involved in zinc homeostasis in the brain. It has been found that alterations in brain zinc status have been implicated in a wide range of neurological disorders including impaired brain development and many neurodegenerative disorders such as Alzheimer's disease, and mood disorders including depression, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and prion disease. Furthermore, zinc has also been implicated in neuronal damage associated with traumatic brain injury, stroke, and seizure. Understanding the mechanisms that control brain zinc homeostasis is thus critical to the development of preventive and treatment strategies for these and other neurological disorders.

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.

Effect of tibolone on dendritic spine density in the rat hippocampus

INTRODUCTION

Oestrogen deficiency produces oxidative stress (OS) and changes in hippocampal neurons and also reduces the density of dendritic spines (DS). These alterations affect the plastic response of the hippocampus. Oestrogen replacement therapy reverses these effects, but it remains to be seen whether the same changes are produced by tibolone (TB). The aim of this study was to test the neuroprotective effects of long-term oral TB treatment and its ability to reverse DS pruning in pyramidal neurons (PN) of hippocampal area CA1.

METHODS

Young Sprague Dawley rats were distributed in 3 groups: a control group in proestrus (Pro) and two ovariectomised groups (Ovx), of which one was provided with a daily TB dose (1mg/kg), OvxTB and the other with vehicle (OvxV), for 40 days in both cases. We analysed lipid peroxidation and DS density in 3 segments of apical dendrites from PNs in hippocampal area CA1.

RESULTS

TB did not reduce lipid peroxidation but it did reverse the spine pruning in CA1 pyramidal neurons of the hippocampus which had been caused by ovariectomy.

CONCLUSIONS

Oestrogen replacement therapy for ovariectomy-induced oestrogen deficiency has a protective effect on synaptic plasticity in the hippocampus.