Perinatal arsenic exposure inhibits binding ability of glucocorticoid receptors to nuclear response elements altering gene expression and affecting learning behavior

Learning deficits in children following arsenic (As) exposure via drinking water have been epidemiologically described in the last decade. Arsenic is a persistent environmental toxin and exposure has been shown to perturb the hypothalamic-pituitary-adrenal (HPA) stress axis. The glucocorticoid receptors (GR) are an integral part of the HPA axis and are found throughout the central nervous system, particularly in the hippocampus, an area of the brain important in learning and memory. The mitogen-activated protein kinase (MAPK) pathway is involved in learning and two kinases of the MAPK pathway, Ras and Raf are transcriptionally regulated by GRs. In the studies detailed in this dissertation the impact of perinatal exposure to 50 parts per billion (ppb) sodium arsenate on learning behavior, GRs and MAPK pathway genes in the C57BL/6J adolescent mouse were examined. Hippocampal-sensitive learning was assessed using a novel object task and eight-way radial arm maze (RAM). Arsenic-exposed offspring showed increased latency to the novel object and increased number of entry errors in the RAM compared to controls. Immunoblotting revealed that arsenic-exposed offspring had significantly lower levels of both GR and mineralocorticoid receptors in the activated nuclear subcellular fraction than controls. As-exposed mice also showed significantly lower Ras and Raf-1 mRNA levels, assessed by real-time RT-PCR, compared to controls. Binding of the glucocorticoid receptor (GR) to glucocorticoid response elements (GREs) in Ras and Raf genes was measured by chromatin immunoprecipitation (ChIP). ChIP revealed reduced binding of the GR to GREs in target genes in the As group. Electrophoretic mobility shift assay (EMSA) revealed intact binding ability in both control and arsenic-exposed offspring to a synthetic GRE. Results suggest that moderate exposures to As can significantly reduce GR levels in the hippocampus, affecting expression of genes that are under the control of the GR and impacting learning behavior. Overall, these data suggest that moderate levels of perinatal As can have a lasting impact on the brain and HPA axis of offspring

Revelations from the Nematode Caenorhabditis elegans on the Complex Interplay of Metal Toxicological Mechanisms

Metals have been definitively linked to a number of disease states. Due to the widespread existence of metals in our environment from both natural and anthropogenic sources, understanding the mechanisms of their cellular detoxification is of upmost importance. Organisms have evolved cellular detoxification systems including glutathione, metallothioneins, pumps and transporters, and heat shock proteins to regulate intracellular metal levels. The model organism, Caenorhabditis elegans (C. elegans), contains these systems and provides several advantages for deciphering the mechanisms of metal detoxification. This review provides a brief summary of contemporary literature on the various mechanisms involved in the cellular detoxification of metals, specifically, antimony, arsenic, cadmium, copper, manganese, mercury, and depleted uranium using the C. elegans model system for investigation and analysis

Revelations from the Nematode Caenorhabditis elegans on the Complex Interplay of Metal Toxicological Mechanisms

Metals have been definitively linked to a number of disease states. Due to the widespread existence of metals in our environment from both natural and anthropogenic sources, understanding the mechanisms of their cellular detoxification is of upmost importance. Organisms have evolved cellular detoxification systems including glutathione, metallothioneins, pumps and transporters, and heat shock proteins to regulate intracellular metal levels. The model organism, Caenorhabditis elegans (C. elegans), contains these systems and provides several advantages for deciphering the mechanisms of metal detoxification. This review provides a brief summary of contemporary literature on the various mechanisms involved in the cellular detoxification of metals, specifically, antimony, arsenic, cadmium, copper, manganese, mercury, and depleted uranium using the C. elegans model system for investigation and analysis

Genome-Wide Analyses of Metal Responsive Genes in Caenorhabditis elegans

Metals are major contaminants that influence human health. Many metals have physiologic roles, but excessive levels can be harmful. Advances in technology have made toxicogenomic analyses possible to characterize the effects of metal exposure on the entire genome. Much of what is known about cellular responses to metals has come from mammalian systems; however the use of non-mammalian species is gaining wider attention. Caenorhabditis elegans is a small round worm whose genome has been fully sequenced and its development from egg to adult is well characterized. It is an attractive model for high throughput screens due to its short lifespan, ease of genetic mutability, low cost, and high homology with humans. Research performed in C. elegans has led to insights in apoptosis, gene expression, and neurodegeneration, all of which can be altered by metal exposure. Additionally, by using worms one can potentially study mechanisms that underline differential responses to metals in nematodes and humans, allowing for identification of novel pathways and therapeutic targets. In this review, toxicogenomic studies performed in C. elegans exposed to various metals will be discussed, highlighting how this non-mammalian system can be utilized to study cellular processes and pathways induced by metals. Recent work focusing on neurodegeneration in Parkinson’s disease will be discussed as an example of the usefulness of genetic screens in C. elegans and the novel findings that can be produced

Perinatal arsenic exposure inhibits binding ability of glucocorticoid receptors to nuclear response elements altering gene expression and affecting learning behavior

Learning deficits in children following arsenic (As) exposure via drinking water have been epidemiologically described in the last decade. Arsenic is a persistent environmental toxin and exposure has been shown to perturb the hypothalamic-pituitary-adrenal (HPA) stress axis. The glucocorticoid receptors (GR) are an integral part of the HPA axis and are found throughout the central nervous system, particularly in the hippocampus, an area of the brain important in learning and memory. The mitogen-activated protein kinase (MAPK) pathway is involved in learning and two kinases of the MAPK pathway, Ras and Raf are transcriptionally regulated by GRs. In the studies detailed in this dissertation the impact of perinatal exposure to 50 parts per billion (ppb) sodium arsenate on learning behavior, GRs and MAPK pathway genes in the C57BL/6J adolescent mouse were examined. Hippocampal-sensitive learning was assessed using a novel object task and eight-way radial arm maze (RAM). Arsenic-exposed offspring showed increased latency to the novel object and increased number of entry errors in the RAM compared to controls. Immunoblotting revealed that arsenic-exposed offspring had significantly lower levels of both GR and mineralocorticoid receptors in the activated nuclear subcellular fraction than controls. As-exposed mice also showed significantly lower Ras and Raf-1 mRNA levels, assessed by real-time RT-PCR, compared to controls. Binding of the glucocorticoid receptor (GR) to glucocorticoid response elements (GREs) in Ras and Raf genes was measured by chromatin immunoprecipitation (ChIP). ChIP revealed reduced binding of the GR to GREs in target genes in the As group. Electrophoretic mobility shift assay (EMSA) revealed intact binding ability in both control and arsenic-exposed offspring to a synthetic GRE. Results suggest that moderate exposures to As can significantly reduce GR levels in the hippocampus, affecting expression of genes that are under the control of the GR and impacting learning behavior. Overall, these data suggest that moderate levels of perinatal As can have a lasting impact on the brain and HPA axis of offspring.The project described was supported by Award Number F31ES017196 (EJM-F) from the National Institute of Environmental Health Sciences, the University of New Mexico Graduate and Professional Society-Graduate Research Development Grant along with the legislature of the state of New Mexico; the Pfizer Global Research and Development Safety Scholars Fellowship and generous funds from the University of New Mexico College of Pharmacy.Biomedical SciencesDoctoralUniversity of New Mexico. Biomedical Sciences Graduate ProgramAllan, AndreaCaldwell, KevinLiu, JimHudson, LaurieSavage, Danie

Untangling the Manganese-α-synuclein Web

Neurodegenerative diseases affect a significant portion of the aging population. Several lines of evidence suggest a positive association between environmental exposures, which are common and cumulative in a lifetime, and development of neurodegenerative diseases. Environmental or occupational exposure to manganese (Mn) has been implicated in neurodegeneration due to its ability to induce mitochondrial dysfunction, oxidative stress and α-synuclein (α-Syn) aggregation. The role of the α-Syn protein vis-a-vis Mn is controversial, as it seemingly plays a duplicitous role in neuroprotection and neurodegeneration. α-Syn has low affinity for Mn, however an indirect interaction cannot be ruled out. In this review we will examine the current knowledge surrounding the interaction of α-Syn and Mn in neurodegenerative process