Early-life exposure to methylmercury in wildtype and pdr-1/parkin knockout C. elegans.

We examined the impact of early-life exposure to methylmercury (MeHg) on Caenorhabditis elegans (C. elegans) pdr-1 mutants, addressing gene-environment interactions. We tested the hypothesis that early-life exposure to MeHg and knockout (KO) of pdr-1 (mammalian: parkin/PARK2) exacerbates MeHg toxicity and damage to the dopaminergic (DAergic) system. pdr-1KO worms showed increased lethality and decreased lifespan following MeHg exposure. Mercury (Hg) content, measured with inductively coupled plasma-mass spectrometry was increased in pdr-1KO worms compared to wildtype (N2) controls. 2'7' dichlorodihydrofluorescein diacetate assay revealed a significant increase in reactive oxygen species in both strains following MeHg exposure; however, while N2 worms showed an increase in skn-1 transcript levels following MeHg exposure, there was no difference in skn-1 induction in pdr-1KO worms. Dopamine-dependent behavioral analysis revealed an effect of MeHg on N2 wildtype worms, but no effect on pdr-1KO worms. Taken together, these results suggest that pdr-1KO worms are more sensitive to MeHg than wildtype worms, but MeHg does not exacerbate behavioral changes related to the absence of pdr-1.

The Role of skn-1 in methylmercury-induced latent dopaminergic neurodegeneration.

Mercury (Hg) is a persistent environmental bioaccumulative metal, with developmental exposure to methylmercury (MeHg) resulting in long-term health effects. We examined the impact of early-life exposure to MeHg and knockdown of skn-1 on dopaminergic (DAergic) neurodegeneration in the nematode Caenorhabditis elegans. SKN-1, a the major stress-activated cytoprotective transcription factors, promotes the transcription of enzymes that scavenge free radicals, synthesizes glutathione and catalyzes reactions that increase xenobiotic excretion. Deletions or mutations in this gene suppress stress resistance. Thus, we hypothesized that the extent of MeHg's toxicity is dependent on intact skn-1 response; therefore skn-1 knockout (KO) worms would show heightened sensitivity to MeHg-induced toxicity compared to wildtype worms. In this study we identified the impact of early-life MeHg exposure on Hg content, stress reactivity and DAergic neurodegeneration in wildtype, and skn-1KO C. elegans. Hg content, measured by Inductively Coupled Plasma Mass Spectrometry, showed no strain-dependent differences. Reactive oxygen species generation was dramatically increased in skn-1KO compared to wildtype worms. Structural integrity of DAergic neurons was microscopically assessed by visualization of fluorescently-labeled neurons, and revealed loss of neurons in skn-1KO and MeHg exposed worms compared to wildtype controls. Dopamine levels detected by High-performance liquid chromatography, were decreased in response to MeHg exposure and decreased in skn-1KO worms, and functional behavioral assays showed similar findings. Combined, these studies suggest that knockdown of skn-1 in the nematode increases DAergic sensitivity to MeHg exposure following a period of latency.

Fast Evaluation of Viral Emerging Risks (FEVER): A computational tool for biosurveillance, diagnostics, and mutation typing of emerging viral pathogens.

Viral pathogens can rapidly evolve, adapt to novel hosts, and evade human immunity. The early detection of emerging viral pathogens through biosurveillance coupled with rapid and accurate diagnostics are required to mitigate global pandemics. However, RNA viruses can mutate rapidly, hampering biosurveillance and diagnostic efforts. Here, we present a novel computational approach called FEVER (Fast Evaluation of Viral Emerging Risks) to design assays that simultaneously accomplish: 1) broad-coverage biosurveillance of an entire group of viruses, 2) accurate diagnosis of an outbreak strain, and 3) mutation typing to detect variants of public health importance. We demonstrate the application of FEVER to generate assays to simultaneously 1) detect sarbecoviruses for biosurveillance; 2) diagnose infections specifically caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); and 3) perform rapid mutation typing of the D614G SARS-CoV-2 spike variant associated with increased pathogen transmissibility. These FEVER assays had a high in silico recall (predicted positive) up to 99.7% of 525,708 SARS-CoV-2 sequences analyzed and displayed sensitivities and specificities as high as 92.4% and 100% respectively when validated in 100 clinical samples. The D614G SARS-CoV-2 spike mutation PCR test was able to identify the single nucleotide identity at position 23,403 in the viral genome of 96.6% SARS-CoV-2 positive samples without the need for sequencing. This study demonstrates the utility of FEVER to design assays for biosurveillance, diagnostics, and mutation typing to rapidly detect, track, and mitigate future outbreaks and pandemics caused by emerging viruses.

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.

Recent Advances in Mercury Research.

Mercury (Hg) is a highly toxic, non-essential, naturally occurring metal with a variety of uses. Mercury is not required for any known biological process and its presence in the human body may be detrimental, especially to the nervous system. Both genetic and behavioral studies suggest that mercury levels, age (both of exposure and at testing), and genetic background determine disease processes and outcome. The metal receptors and genes responsible for mercury metabolism also appear to play a pivotal role in the etiology of mercury-induced pathology. This review presents information about the latest advances in mercury research, with particular focus on low-level exposures and the contribution of genetics to toxic outcome. Future studies should address the contribution of genetics and low-level mercury exposure to disease, namely gene x environment interactions, taking into consideration age of exposure as developing animals are exquisitely more sensitive to this metal. In addition to recent advances in understanding the pathology associated with mercury exposure, the review highlights transport mechanisms, cellular distribution and detoxification of mercury species in the body.

Manganese neurotoxicity and the role of reactive oxygen species.

Manganese (Mn) is an essential dietary nutrient, but an excess or accumulation can be toxic. Disease states, such as manganism, are associated with overexposure or accumulation of Mn and are due to the production of reactive oxygen species, free radicals, and toxic metabolites; alteration of mitochondrial function and ATP production; and depletion of cellular antioxidant defense mechanisms. This review focuses on all of the preceding mechanisms and the scientific studies that support them as well as providing an overview of the absorption, distribution, and excretion of Mn and the stability and transport of Mn compounds in the body.

Metal-induced neurodegeneration in C. elegans.

The model species, Caenorhabditis elegans, has been used as a tool to probe for mechanisms underlying numerous neurodegenerative diseases. This use has been exploited to study neurodegeneration induced by metals. The allure of the nematode comes from the ease of genetic manipulation, the ability to fluorescently label neuronal subtypes, and the relative simplicity of the nervous system. Notably, C. elegans have approximately 60-80% of human genes and contain genes involved in metal homeostasis and transport, allowing for the study of metal-induced degeneration in the nematode. This review discusses methods to assess degeneration as well as outlines techniques for genetic manipulation and presents a comprehensive survey of the existing literature on metal-induced degeneration studies in the worm.

Cellular transport and homeostasis of essential and nonessential metals.

Metals can have a number of detrimental or beneficial effects in the cell, but first they must get in. Organisms have evolved transport mechanisms to get metals that are required, or essential into the cell. Nonessential metals often enter the cell through use of the machinery provided for essential metals. Much work has been done to advance our understanding of how these metals are transported across plasma and organelle membranes. This review provides an overview of essential and nonessential metal transport and homeostatic processes.

Mechanisms and Modifiers of Methylmercury-Induced Neurotoxicity.

The neurotoxic consequences of methylmercury (MeHg) exposure have long been known, however a complete understanding of the mechanisms underlying this toxicity is elusive. Recent epidemiological and experimental studies have provided many mechanistic insights, particularly into the contribution of genetic and environmental factors that interact with MeHg to modify toxicity. This review will outline cellular processes directly and indirectly affected by MeHg, including oxidative stress, cellular signaling and gene expression, and discuss genetic, environmental and nutritional factors capable of modifying MeHg toxicity.

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.

Reduced expression of MAPK/ERK genes in perinatal arsenic-exposed offspring induced by glucocorticoid receptor deficits.

Changes within the glucocorticoid receptor (GR) cellular signaling pathway were evaluated in adolescent mice exposed to 50 ppb arsenic during gestation. Previously, we reported increased basal plasma corticosterone levels, decreased hippocampal GR levels and deficits in learning and memory performance in perinatal arsenic-exposed mice. The biosynthesis of members of the mitogen-activated protein kinase (MAPK) signaling pathway, known to be involved in learning and memory, is modulated by the binding of GR to glucocorticoid response elements (GREs) in the gene promoters. Two genes of the MAPK pathway, Ras and Raf, contain GREs which are activated upon binding of GRs. We evaluated the activity of GRs at Ras and Raf promoters using chromatin immunoprecipitation and real-time PCR and report decreased binding of the GR at these promoters. An ELISA-based GR binding assay was used to explore whether this decreased binding was restricted to in vivo promoters and revealed no differences in binding of native GR to synthetic GREs. The decreased in vivo GR binding coincides with significantly decreased mRNA levels and slight reductions of protein of both H-Ras and Raf-1 in perinatally arsenic-exposed mice. Nuclear activated extracellular-signal regulated kinase (ERK), a downstream target of Ras and Raf, whose transcriptional targets also play an important role in learning and memory, was decreased in the hippocampus of arsenic-exposed animals when compared to controls. GR-mediated transcriptional deficits in the MAPK/ERK pathway could be an underlying cause of previously reported learning deficits and provide the link to arsenic-induced deficiencies in cognitive development.

Insights from Caenorhabditis elegans on the role of metals in neurodegenerative diseases.

Neurodegeneration is characterized by the cell death or loss of structure and/or function of neurons. Many neurodegenerative diseases including Parkinson's disease (PD) and Alzheimer's disease (AD) are the result of neurodegenerative processes. Metals are essential for many life processes, but they are also culpable for several neurodegenerative mechanisms. In this review, we discuss the role of metals in neurodegenerative diseases with emphasis on the utility of Caenorhabditis elegans (C. elegans) genetic models in deciphering mechanisms associated with the etiology of PD and AD.

Learning deficits in C57BL/6J mice following perinatal arsenic exposure: consequence of lower corticosterone receptor levels?

Most studies on arsenic as a drinking water contaminant have focused on its carcinogenic potential but a few suggest that arsenic can adversely affect cognitive development. One parameter of the hypothalamic-pituitary-adrenal axis, the corticosterone receptor (CR) has been shown to be altered by arsenic. These receptors are found throughout the central nervous system, particularly in the hippocampus, an area of the brain of central importance for learning and memory. We examined the impact of perinatal exposure to 50 parts per billion (ppb) sodium arsenate on CRs and learning and memory behavior in the C57BL/6J mouse. Measurements of CRs revealed that arsenic-exposed offspring have significantly lower levels of these receptors in the nucleus than controls. Exposed offspring showed longer latency to approach a novel object than controls in an object recognition task. In the 8-way radial arm maze, arsenic offspring had a significant increase in the number of entry errors compared to controls. Results suggest that moderate exposures to perinatal arsenic can significantly reduce CR levels in the hippocampus and can have adverse effects on learning and memory behavior.