Methylmercury inhibits cysteine uptake in cultured primary astrocytes, but not in neurons

Gouri Shanker; Jeffrey W. Allen; Lysette A. Mutkus; Michael Aschner

doi:10.1016/S0006-8993(01)02791-3

Methylmercury inhibits cysteine uptake in cultured primary astrocytes, but not in neurons

Gouri Shanker, Jeffrey W. Allen, Lysette A. Mutkus, Michael Aschner

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45 Scopus citations

Abstract

The maintenance of adequate intracellular glutathione (GSH) concentrations is dependent on the availability and transport of the rate-limiting substrate, cysteine. A suggested mechanism of methylmercury (MeHg) neurotoxicity in brain involves the formation of oxygen radicals, and a decrease in intracellular levels of GSH. Recently, we have characterized various cysteine transport systems (both Na⁺-dependent and -independent) in cerebrocortical astrocytes and hippocampal neurons. The present study was carried out to investigate the effect of MeHg on cysteine uptake in both astrocytes and neurons, and to determine whether cysteine transport is differentially affected in the two cell types by MeHg treatment. Sixty-minute pretreatment with MeHg caused significant concentration-dependent inhibition in cysteine uptake in astrocytes, but not in neurons. As most of the cysteine transport is Na⁺-dependent (80-90% of total), additional studies focused on MeHg's effect on the Na⁺-dependent cysteine transporters X_AG- and ASC. An additive inhibitory effect on cysteine uptake was observed in astrocytes treated with MeHg (5 μM) plus sub-maximal inhibitory concentrations (0.1 and 0.5 mM) of threo-β-hydroxy-aspartate (THA), a specific inhibitor of the Na⁺-dependent transporter, X_AG-, compared to astrocytes treated with MeHg (P<0.001) or THA alone (P<0.05). There was no additive effect of MeHg and maximal inhibitory concentrations of THA (1.0 and 5.0 mM) on astrocytic cysteine uptake inhibition. Additional studies examined the sensitivity of the Na⁺-dependent ASC transport system to MeHg treatment. Maximal inhibitory concentration of L-serine (10 mM) alone had a rather modest inhibitory effect on cysteine uptake, and when applied in the presence of MeHg there was no additive effect. These results suggest that the inhibition of cysteine uptake by MeHg in astrocytes occurs through specific inhibition of both the X_AG- as well as the ASC transport system.

Original language	English (US)
Pages (from-to)	159-165
Number of pages	7
Journal	Brain research
Volume	914
Issue number	1-2
DOIs	https://doi.org/10.1016/S0006-8993(01)02791-3
State	Published - Sep 28 2001
Externally published	Yes

Keywords

Astrocytes
Cysteine
Glutathione
In vitro
Methlmercury
Neurons
Transport

ASJC Scopus subject areas

General Neuroscience
Molecular Biology
Clinical Neurology
Developmental Biology

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10.1016/S0006-8993(01)02791-3

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title = "Methylmercury inhibits cysteine uptake in cultured primary astrocytes, but not in neurons",

abstract = "The maintenance of adequate intracellular glutathione (GSH) concentrations is dependent on the availability and transport of the rate-limiting substrate, cysteine. A suggested mechanism of methylmercury (MeHg) neurotoxicity in brain involves the formation of oxygen radicals, and a decrease in intracellular levels of GSH. Recently, we have characterized various cysteine transport systems (both Na+-dependent and -independent) in cerebrocortical astrocytes and hippocampal neurons. The present study was carried out to investigate the effect of MeHg on cysteine uptake in both astrocytes and neurons, and to determine whether cysteine transport is differentially affected in the two cell types by MeHg treatment. Sixty-minute pretreatment with MeHg caused significant concentration-dependent inhibition in cysteine uptake in astrocytes, but not in neurons. As most of the cysteine transport is Na+-dependent (80-90% of total), additional studies focused on MeHg's effect on the Na+-dependent cysteine transporters XAG- and ASC. An additive inhibitory effect on cysteine uptake was observed in astrocytes treated with MeHg (5 μM) plus sub-maximal inhibitory concentrations (0.1 and 0.5 mM) of threo-β-hydroxy-aspartate (THA), a specific inhibitor of the Na+-dependent transporter, XAG-, compared to astrocytes treated with MeHg (P<0.001) or THA alone (P<0.05). There was no additive effect of MeHg and maximal inhibitory concentrations of THA (1.0 and 5.0 mM) on astrocytic cysteine uptake inhibition. Additional studies examined the sensitivity of the Na+-dependent ASC transport system to MeHg treatment. Maximal inhibitory concentration of L-serine (10 mM) alone had a rather modest inhibitory effect on cysteine uptake, and when applied in the presence of MeHg there was no additive effect. These results suggest that the inhibition of cysteine uptake by MeHg in astrocytes occurs through specific inhibition of both the XAG- as well as the ASC transport system.",

keywords = "Astrocytes, Cysteine, Glutathione, In vitro, Methlmercury, Neurons, Transport",

author = "Gouri Shanker and Allen, {Jeffrey W.} and Mutkus, {Lysette A.} and Michael Aschner",

note = "Funding Information: The authors gratefully acknowledge the laboratory of Dr. Robert E. Hampson for providing neuronal cultures. A Public Health Service grant from the National Institutes of Health, NIEHS 07331, provided support for this study.",

year = "2001",

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doi = "10.1016/S0006-8993(01)02791-3",

language = "English (US)",

volume = "914",

pages = "159--165",

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T1 - Methylmercury inhibits cysteine uptake in cultured primary astrocytes, but not in neurons

AU - Shanker, Gouri

AU - Allen, Jeffrey W.

AU - Mutkus, Lysette A.

AU - Aschner, Michael

N1 - Funding Information: The authors gratefully acknowledge the laboratory of Dr. Robert E. Hampson for providing neuronal cultures. A Public Health Service grant from the National Institutes of Health, NIEHS 07331, provided support for this study.

PY - 2001/9/28

Y1 - 2001/9/28

N2 - The maintenance of adequate intracellular glutathione (GSH) concentrations is dependent on the availability and transport of the rate-limiting substrate, cysteine. A suggested mechanism of methylmercury (MeHg) neurotoxicity in brain involves the formation of oxygen radicals, and a decrease in intracellular levels of GSH. Recently, we have characterized various cysteine transport systems (both Na+-dependent and -independent) in cerebrocortical astrocytes and hippocampal neurons. The present study was carried out to investigate the effect of MeHg on cysteine uptake in both astrocytes and neurons, and to determine whether cysteine transport is differentially affected in the two cell types by MeHg treatment. Sixty-minute pretreatment with MeHg caused significant concentration-dependent inhibition in cysteine uptake in astrocytes, but not in neurons. As most of the cysteine transport is Na+-dependent (80-90% of total), additional studies focused on MeHg's effect on the Na+-dependent cysteine transporters XAG- and ASC. An additive inhibitory effect on cysteine uptake was observed in astrocytes treated with MeHg (5 μM) plus sub-maximal inhibitory concentrations (0.1 and 0.5 mM) of threo-β-hydroxy-aspartate (THA), a specific inhibitor of the Na+-dependent transporter, XAG-, compared to astrocytes treated with MeHg (P<0.001) or THA alone (P<0.05). There was no additive effect of MeHg and maximal inhibitory concentrations of THA (1.0 and 5.0 mM) on astrocytic cysteine uptake inhibition. Additional studies examined the sensitivity of the Na+-dependent ASC transport system to MeHg treatment. Maximal inhibitory concentration of L-serine (10 mM) alone had a rather modest inhibitory effect on cysteine uptake, and when applied in the presence of MeHg there was no additive effect. These results suggest that the inhibition of cysteine uptake by MeHg in astrocytes occurs through specific inhibition of both the XAG- as well as the ASC transport system.

AB - The maintenance of adequate intracellular glutathione (GSH) concentrations is dependent on the availability and transport of the rate-limiting substrate, cysteine. A suggested mechanism of methylmercury (MeHg) neurotoxicity in brain involves the formation of oxygen radicals, and a decrease in intracellular levels of GSH. Recently, we have characterized various cysteine transport systems (both Na+-dependent and -independent) in cerebrocortical astrocytes and hippocampal neurons. The present study was carried out to investigate the effect of MeHg on cysteine uptake in both astrocytes and neurons, and to determine whether cysteine transport is differentially affected in the two cell types by MeHg treatment. Sixty-minute pretreatment with MeHg caused significant concentration-dependent inhibition in cysteine uptake in astrocytes, but not in neurons. As most of the cysteine transport is Na+-dependent (80-90% of total), additional studies focused on MeHg's effect on the Na+-dependent cysteine transporters XAG- and ASC. An additive inhibitory effect on cysteine uptake was observed in astrocytes treated with MeHg (5 μM) plus sub-maximal inhibitory concentrations (0.1 and 0.5 mM) of threo-β-hydroxy-aspartate (THA), a specific inhibitor of the Na+-dependent transporter, XAG-, compared to astrocytes treated with MeHg (P<0.001) or THA alone (P<0.05). There was no additive effect of MeHg and maximal inhibitory concentrations of THA (1.0 and 5.0 mM) on astrocytic cysteine uptake inhibition. Additional studies examined the sensitivity of the Na+-dependent ASC transport system to MeHg treatment. Maximal inhibitory concentration of L-serine (10 mM) alone had a rather modest inhibitory effect on cysteine uptake, and when applied in the presence of MeHg there was no additive effect. These results suggest that the inhibition of cysteine uptake by MeHg in astrocytes occurs through specific inhibition of both the XAG- as well as the ASC transport system.

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KW - Cysteine

KW - Glutathione

KW - In vitro

KW - Methlmercury

KW - Neurons

KW - Transport

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ER -

Methylmercury inhibits cysteine uptake in cultured primary astrocytes, but not in neurons

Abstract

Keywords

ASJC Scopus subject areas

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