TY - JOUR
T1 - Methylmercury alters the in vitro uptake of glutamate in GLAST- and GLT-1-transfected mutant CHO-K1 cells
AU - Mutkus, Lysette
AU - Aschner, Judy L.
AU - Syversen, Tore
AU - Aschner, Michael
N1 - Funding Information:
This study was supported by Public Health Service grant ES07331 to MA.
PY - 2005/12
Y1 - 2005/12
N2 - In order to maintain normal functioning of the brain, glutamate homeostasis and extracellular levels of excitotoxic amino acids (EAA) must be tightly controlled. This is accomplished, in large measure, by the astroglial high-affinity Na+-dependent EAA transporters glutamate/ aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1). Methylmercury (MeHg) is a potent neurotoxicant. Astrocytes are known targets for MeHg toxicity representing a site for mercury localization. MeHg is known to cause astrocytic swelling, EAA release, and uptake inhibition in astrocytes, leading to increased extracellular glutamate levels and ensuing neuronal excitotoxicity and degeneration. However, the mechanisms and contribution of specific glutamate transporters to MeHg-induced glutamate dyshomeostasis remain unknown. Accordingly, the present study was carried out to investigate the effects of MeHg on the transport of [D-2, 3-3H]-D-aspartate, a nonmetabolizable glutamate analog in Chinese hamster ovary cells (CHO) transfected with the glutamate transporter subtypes GLAST or GLT-1. Additional studies examined the effects of MeHg on mRNA and protein levels of these transporters. Our results indicate the following (1) MeHg selectively affects glutamate transporter mRNA expression. MeHg treatment (6 h) led to no discernible changes in GLAST mRNA expression; however, GLT-1 mRNA expression significantly (p < 0.001) increased following treatments with 5 or 10 μM MeHg. (2) Selective changes in the expression of glutamate transporter protein levels were also noted. GLAST transporter protein levels significantly (p < 0.001, both at 5 and 10 μM MeHg) increased and GLT-1 transporter protein levels significantly (p < 0.001) decreased following MeHg exposure (5 μM). (3) MeHg exposure led to significant inhibition (p < 0.05) of glutamate uptake by GLAST (both 5 and 10 μM MeHg), whereas GLT-1 transporter activity was significantly (p < 0.01) increased following exposure to 5 and 10 μM MeHg. These studies suggest that MeHg contributes to the dysregulation of glutamate homeostasis and that its effects are distinct for GLAST and GLT-1.
AB - In order to maintain normal functioning of the brain, glutamate homeostasis and extracellular levels of excitotoxic amino acids (EAA) must be tightly controlled. This is accomplished, in large measure, by the astroglial high-affinity Na+-dependent EAA transporters glutamate/ aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1). Methylmercury (MeHg) is a potent neurotoxicant. Astrocytes are known targets for MeHg toxicity representing a site for mercury localization. MeHg is known to cause astrocytic swelling, EAA release, and uptake inhibition in astrocytes, leading to increased extracellular glutamate levels and ensuing neuronal excitotoxicity and degeneration. However, the mechanisms and contribution of specific glutamate transporters to MeHg-induced glutamate dyshomeostasis remain unknown. Accordingly, the present study was carried out to investigate the effects of MeHg on the transport of [D-2, 3-3H]-D-aspartate, a nonmetabolizable glutamate analog in Chinese hamster ovary cells (CHO) transfected with the glutamate transporter subtypes GLAST or GLT-1. Additional studies examined the effects of MeHg on mRNA and protein levels of these transporters. Our results indicate the following (1) MeHg selectively affects glutamate transporter mRNA expression. MeHg treatment (6 h) led to no discernible changes in GLAST mRNA expression; however, GLT-1 mRNA expression significantly (p < 0.001) increased following treatments with 5 or 10 μM MeHg. (2) Selective changes in the expression of glutamate transporter protein levels were also noted. GLAST transporter protein levels significantly (p < 0.001, both at 5 and 10 μM MeHg) increased and GLT-1 transporter protein levels significantly (p < 0.001) decreased following MeHg exposure (5 μM). (3) MeHg exposure led to significant inhibition (p < 0.05) of glutamate uptake by GLAST (both 5 and 10 μM MeHg), whereas GLT-1 transporter activity was significantly (p < 0.01) increased following exposure to 5 and 10 μM MeHg. These studies suggest that MeHg contributes to the dysregulation of glutamate homeostasis and that its effects are distinct for GLAST and GLT-1.
KW - GLAST
KW - GLT-1
KW - Glutamate transport
KW - Methylmercury
KW - Neurotoxicity
UR - http://www.scopus.com/inward/record.url?scp=27844497048&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=27844497048&partnerID=8YFLogxK
U2 - 10.1385/BTER:107:3:231
DO - 10.1385/BTER:107:3:231
M3 - Article
C2 - 16286679
AN - SCOPUS:27844497048
SN - 0163-4984
VL - 107
SP - 231
EP - 245
JO - Biological Trace Element Research
JF - Biological Trace Element Research
IS - 3
ER -
