Peres TV et al. (2018) Biol Trace Elem Res "Small Molecule Modifiers of In Vitro Manganese Transport Alter Toxicity In Vivo."

Bornhorst J, Horning KJ, Bowman AB, Schwerdtle T, Peres TV, Aschner M

[Biol Trace Elem Res, 2018]

Manganese (Mn) is essential for several species and daily requirements are commonly met by an adequate diet. Mn overload may cause motor and psychiatric disturbances and may arise from an impaired or not fully developed excretion system, transporter malfunction and/or exposure to excessive levels of Mn. Therefore, deciphering processes regulating neuronal Mn homeostasis is essential to understand the mechanisms of Mn neurotoxicity. In the present study, we selected two small molecules (with opposing effects on Mn transport) from a previous high throughput screen of 40,167 to test their effects on Mn toxicity parameters in vivo using Caenorhabditis elegans. We pre-exposed worms to VU0063088 and VU0026921 for 30min followed by co-exposure for 1h with Mn and evaluated Mn accumulation, dopaminergic (DAergic) degeneration and worm survival. Control worms were exposed to vehicle (DMSO) and saline only. In pdat-1::GFP worms, with GFP labeled DAergic neurons, we observed a decrease of Mn-induced DAergic degeneration in the presence of both small molecules. This effect was also observed in an smf-2 knockout strain. SMF-2 is a regulator of Mn transport in the worms and this strain accumulates higher Mn levels. We did not observe improved survival in the presence of small molecules. Our results suggest that both VU0063088 and VU0026921 may modulate Mn levels in the worms through a mechanism that does not require SMF-2 and induce protection against Mn neurotoxicity.

Chen P et al. (2015) Toxicol Res (Camb) "Manganese-induced Neurotoxicity: From C. elegans to Humans."

Peres TV, Chakraborty S, Bowman AB, Aschner M, Chen P

[Toxicol Res (Camb), 2015]

Manganese (Mn) is one of the most abundant metals on the earth. It is required for normal cellular activities, but overexposure leads to toxicity. Neurons are more susceptible to Mn-induced toxicity than other cells, and accumulation of Mn in the brain results in Manganism that presents with Parkinson's disease (PD)-like symptoms. In the last decade, a number of Mn transporters have been identified, which improves our understanding of Mn transport in and out of cells. However, the mechanism of Mn-induced neurotoxicity is only partially uncovered, with further research needed to explore the whole picture of Mn-induced toxicity. In this review, we will address recent progress in Mn-induced neurotoxicity from C. elegans to humans, and explore future directions that will help understand the mechanisms of its neurotoxicity.

Taylor CA et al. (2020) J Nutr "Maintaining Translational Relevance in Animal Models of Manganese Neurotoxicity."

Mukhopadhyay S, Tuschl K, Bornhorst J, Nicolai MM, Aschner M, Taylor CA, Gubert P, Varao AM, Smith DR

[J Nutr, 2020]

Manganese is an essential metal, but elevated brain Mn concentrations produce a parkinsonian-like movement disorder in adults and fine motor, attentional, cognitive, and intellectual deficits in children. Human Mn neurotoxicity occurs owing to elevated exposure from occupational or environmental sources, defective excretion (e.g., due to cirrhosis), or loss-of-function mutations in the Mn transporters solute carrier family 30 member 10 or solute carrier family 39 member 14. Animal models are essential to study Mn neurotoxicity, but in order to be translationally relevant, such models should utilize environmentally relevant Mn exposure regimens that reproduce changes in brain Mn concentrations and neurological function evident in human patients. Here, we provide guidelines for Mn exposure in mice, rats, nematodes, and zebrafish so that brain Mn concentrations and neurobehavioral sequelae remain directly relatable to the human phenotype.

Ke T et al. (2019) Neurochem Res "Role of Astrocytes in Manganese Neurotoxicity Revisited."

Rizor A, Lee E, Ke T, Sidoryk-Wegrzynowicz M, Pajarillo E, Aschner M, Soares FAA

[Neurochem Res, 2019]

Manganese (Mn) overexposure is a public health concern due to its widespread industrial usage and the risk for environmental contamination. The clinical symptoms of Mn neurotoxicity, or manganism, share several pathological features of Parkinson's disease (PD). Biologically, Mn is an essential trace element, and Mn in the brain is preferentially localized in astrocytes. This review summarizes the role of astrocytes in Mn-induced neurotoxicity, specifically on the role of neurotransmitter recycling, neuroinflammation, and genetics. Mn overexposure can dysregulate astrocytic cycling of glutamine (Gln) and glutamate (Glu), which is the basis for Mn-induced excitotoxic neuronal injury. In addition, reactive astrocytes are important mediators of Mn-induced neuronal damage by potentiating neuroinflammation. Genetic studies, including those with Caenorhabditis elegans (C. elegans) have uncovered several genes associated with Mn neurotoxicity. Though we have yet to fully understand the role of astrocytes in the pathologic changes characteristic of manganism, significant strides have been made over the last two decades in deciphering the role of astrocytes in Mn-induced neurotoxicity and neurodegeneration.

Peres TV et al. (2016) BMC Pharmacol Toxicol ""Manganese-induced neurotoxicity: a review of its behavioral consequences and neuroprotective strategies"."

Peres TV, Schettinger MR, Aschner M, Carvalho F, Bowman AB, Chen P, Avila DS

[BMC Pharmacol Toxicol, 2016]

Manganese (Mn) is an essential heavy metal. However, Mn's nutritional aspects are paralleled by its role as a neurotoxicant upon excessive exposure. In this review, we covered recent advances in identifying mechanisms of Mn uptake and its molecular actions in the brain as well as promising neuroprotective strategies. The authors focused on reporting findings regarding Mn transport mechanisms, Mn effects on cholinergic system, behavioral alterations induced by Mn exposure and studies of neuroprotective strategies against Mn intoxication. We report that exposure to Mn may arise from environmental sources, occupational settings, food, total parenteral nutrition (TPN), methcathinone drug abuse or even genetic factors, such as mutation in the transporter SLC30A10. Accumulation of Mn occurs mainly in the basal ganglia and leads to a syndrome called manganism, whose symptoms of cognitive dysfunction and motor impairment resemble Parkinson's disease (PD). Various neurotransmitter systems may be impaired due to Mn, especially dopaminergic, but also cholinergic and GABAergic. Several proteins have been identified to transport Mn, including divalent metal tranporter-1 (DMT-1), SLC30A10, transferrin and ferroportin and allow its accumulation in the central nervous system. Parallel to identification of Mn neurotoxic properties, neuroprotective strategies have been reported, and these include endogenous antioxidants (for instance, vitamin E), plant extracts (complex mixtures containing polyphenols and non-characterized components), iron chelating agents, precursors of glutathione (GSH), and synthetic compounds that can experimentally afford protection against Mn-induced neurotoxicity.

Gubert P et al. (2018) Neurotoxicology "Metabolic effects of manganese in the nematode Caenorhabditis elegans through DAergic pathway and transcription factors activation."

Trindade LS, Aschner M, Lehmen T, Cheng P, Soares FAA, Fessel JP, Bornhorst J, Avila DS, Gubert P, Puntel B

[Neurotoxicology, 2018]

Manganese (Mn) is an essential trace element for physiological functions since it acts as an enzymatic co-factor. Nevertheless, overexposure to Mn has been associated with a pathologic condition called manganism. Furthermore, Mn has been reported to affect lipid metabolism by mechanisms which have yet to be established. Herein, we used the nematode Caenorhabditis elegans to examine Mn's effects on the dopaminergic (DAergic) system and determine which transcription factors that regulate with lipid metabolism are affected by it. Worms were exposed to Mn for four hours in the presence of bacteria and in a liquid medium (85mM NaCl). Mn increased fat storage as evidenced both by Oil Red O accumulation and triglyceride levels. In addition, metabolic activity was reduced as a reflection of decreased oxygen consumption caused by Mn. Mn also affected feeding behavior as evidenced by decreased pharyngeal pumping rate. DAergic neurons viability were not altered by Mn, however the dopamine levels were significantly reduced following Mn exposure. Furthermore, the expression of sbp-1 transcription factor and let-363 protein kinase responsible for lipid accumulation control was increased and decreased, respectively, by Mn. Altogether, our data suggest that Mn increases the fat storage in C. elegans, secondary to DAergic system alterations, under the control of SBP-1 and LET-363 proteins.

Leyva-Illades D et al. (2014) J Neurosci "SLC30A10 is a cell surface-localized manganese efflux transporter, and parkinsonism-causing mutations block its intracellular trafficking and efflux activity."

Mukhopadhyay S, Hutchens S, Morrisett RA, Mercado JM, Zogzas CE, Swaim CD, Bowman AB, Aschner M, Leyva-Illades D, Chen P

[J Neurosci, 2014]

Manganese (Mn) is an essential metal, but elevated cellular levels are toxic and may lead to the development of an irreversible parkinsonian-like syndrome that has no treatment. Mn-induced parkinsonism generally occurs as a result of exposure to elevated Mn levels in occupational or environmental settings. Additionally, patients with compromised liver function attributable to diseases, such as cirrhosis, fail to excrete Mn and may develop Mn-induced parkinsonism in the absence of exposure to elevated Mn. Recently, a new form of familial parkinsonism was reported to occur as a result of mutations in SLC30A10. The cellular function of SLC30A10 and the mechanisms by which mutations in this protein cause parkinsonism are unclear. Here, using a combination of mechanistic and functional studies in cell culture, Caenorhabditis elegans, and primary midbrain neurons, we show that SLC30A10 is a cell surface-localized Mn efflux transporter that reduces cellular Mn levels and protects against Mn-induced toxicity. Importantly, mutations in SLC30A10 that cause familial parkinsonism blocked the ability of the transporter to traffic to the cell surface and to mediate Mn efflux. Although expression of disease-causing SLC30A10 mutations were not deleterious by themselves, neurons and worms expressing these mutants exhibited enhanced sensitivity to Mn toxicity. Our results provide novel insights into the mechanisms involved in the onset of a familial form of parkinsonism and highlight the possibility of using enhanced Mn efflux as a therapeutic strategy for the potential management of Mn-induced parkinsonism, including that occurring as a result of mutations in SLC30A10.

Nicolai MM et al. (2021) Int J Mol Sci "Effects of Manganese on Genomic Integrity in the Multicellular Model Organism Caenorhabditis elegans."

Brinkmann V, Gremme A, Winkelbeiner N, Baesler J, Schwerdtle T, Aschner M, Weishaupt AK, Fritz G, Bornhorst J, Nicolai MM, Wellenberg A

[Int J Mol Sci, 2021]

Although manganese (Mn) is an essential trace element, overexposure is associated with Mn-induced toxicity and neurological dysfunction. Even though Mn-induced oxidative stress is discussed extensively, neither the underlying mechanisms of the potential consequences of Mn-induced oxidative stress on DNA damage and DNA repair, nor the possibly resulting toxicity are characterized yet. In this study, we use the model organism <i>Caenorhabditis elegans</i> to investigate the mode of action of Mn toxicity, focusing on genomic integrity by means of DNA damage and DNA damage response. Experiments were conducted to analyze Mn bioavailability, lethality, and induction of DNA damage. Different deletion mutant strains were then used to investigate the role of base excision repair (BER) and dePARylation (DNA damage response) proteins in Mn-induced toxicity. The results indicate a dose- and time-dependent uptake of Mn, resulting in increased lethality. Excessive exposure to Mn decreases genomic integrity and activates BER. Altogether, this study characterizes the consequences of Mn exposure on genomic integrity and therefore broadens the molecular understanding of pathways underlying Mn-induced toxicity. Additionally, studying the basal poly(ADP-ribosylation) (PARylation) of worms lacking poly(ADP-ribose) glycohydrolase (PARG) <i>parg-1</i> or <i>parg-2</i> (two orthologue of PARG), indicates that <i>parg-1</i> accounts for most of the glycohydrolase activity in worms.

Catherine Au et al. (2008) C.elegans Neuronal Development Meeting "Manganese Transport in C. elegans: the Role of the SMF Genes"

Michael Aschner, Catherine Au, Keith Erikson, Joel Anderson, Alexandre Benedetto

[C.elegans Neuronal Development Meeting, 2008]

Manganese (Mn) is an essential trace element for normal human development and vital enzymatic activities. However, occupational exposure to high levels of Mn has been implicated in a Parkinsonian-like syndrome known as manganism. Since the initial discovery of Mn-induced pathogenesis, much effort has been put forth in order to study the mechanism of uptake and the potential adverse effect of manganism. In the present study, we use C. elegans to understand the mechanisms of Mn transport across biological membranes. In wildtype (WT) C. elegans, acute Mn treatment induces strong osmotic defects eventually leading to death. It was shown in mammalian systems that Mn can cross the blood-brain barrier through the divalent metal transporter DMT1/NRAMP2. The C. elegans genome encodes three DMT1 orthologues (SMF-1, SMF-2, SMF-3). When compared with WT, C. elegans deletion-mutants smf-1(eh5) and smf-3(ok1035) exhibited an increased resistance to Mn exposure while smf-2(gk1330) was more sensitive. In accordance with those observations, the Mn content ofsmf-2(gk1330) after Mn exposure was greater than WT, smf-1(eh5) and smf-3(ok1035), the latter taking up less Mn than all the other mutants. SMF-1::GFP and SMF-3::GFP were found co-expressed in the gut and the major epidermis hyp7, which likely account for most Mn uptake, while SMF-2::GFP was mainly expressed in the mc1-3 and vpi1-6 cells. The combination of our data allows us to propose a model for Mn transport and SMF roles in C. elegans. This work establishes C. elegans as a valuable model to study Mn transport and toxicity. Given the similarity of DMT1/NRAMP2-related genes from worms to human, it may also provide insights into the Mn-dependent regulation of the NRAMP family of proteins in vertebrates. This project is funded by R01 ES10563 to MA.

Raj V et al. (2021) Biochem Biophys Res Commun "Manganese exposure during early larval stages of C.elegans causes learning disability in the adult stage."

Nair A, Thekkuveettil A, Raj V

[Biochem Biophys Res Commun, 2021]

Manganese (Mn), even though an essential trace element, causes neurotoxicity in excess. In adults, over-exposure to Mn causes clinical manifestations, including dystonia, progressive bradykinesia, disturbance of gait, slurring, and stuttering of speech. These symptoms are mainly because of Mn-associated oxidative stress and degeneration of dopamine neurons in the central nervous system. Children with excessive Mn exposure often show learning disabilities but rarely show symptoms associated with dopaminergic neuron dysfunction. It is unclear why Mn exposure shows distinctive clinical outcomes in developing brains versus adult brains. Studies on nematode C.elegans have demonstrated that it is an excellent model to elucidate Mn-associated toxicity in the nervous system. In this study, we chronically exposed Mn to L1 larval stage of the worms to understand the effects on dopamine neurons and cognitive development. The worms showed modified behavior to exogenous dopamine compared to the control. The dopamine neurons showed resistance to neurodegeneration on repeated Mn exposure during the adult stage. As observed in mammalian systems, these worms showed significantly low olfactory adaptive learning and memory. This study shows that C.elegans alters adaptive developmental plasticity during Mn overexposure, modifying its sensitivity towards the metal ion and leads to remodeling in its innate learning behavior.