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Thiamine deficiency results in downregulation of the GLAST glutamate transporter in cultured astrocytes
Author(s) -
Hazell Alan S.,
Pannunzio Pierre,
Rama Rao K.V.,
Pow David V.,
Rambaldi Andrea
Publication year - 2003
Publication title -
glia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.954
H-Index - 164
eISSN - 1098-1136
pISSN - 0894-1491
DOI - 10.1002/glia.10241
Subject(s) - glutamate receptor , downregulation and upregulation , glutamate aspartate transporter , astrocyte , thiamine , biology , metabotropic glutamate receptor , endocrinology , transporter , biochemistry , medicine , receptor , central nervous system , gene
Abstract Pyrithiamine‐induced thiamine deficiency (TD) is a well‐established model of Wernicke's encephalopathy in which a glutamate‐mediated excitotoxic mechanism may play an important role in determining selective vulnerability. In order to examine this possibility, cultured astrocytes were exposed to TD and effects on glutamate transport and metabolic function were studied. TD led to decreases in cellular levels of thiamine and thiamine diphosphate (TDP) after 24 h of treatment and decreased activities of the TDP‐dependent enzymes α‐ketoglutarate dehydrogenase and transketolase after 4 and 7 days, respectively. TD treatment for 10 days led to a reversible decrease in the uptake of [ 3 H]‐D‐aspartate, a nonmetabolizable analogue of glutamate. Kinetic analysis revealed that the uptake inhibition was caused by a 47% decrease in the V max for uptake of [ 3 H]‐D‐aspartate, with no change in the K m value. Immunoblotting showed that this decrease in uptake was due to an 81% downregulation of the astrocyte‐specific GLAST glutamate transporter. Loss of uptake activity and GLAST protein were blocked by treatment with the protein kinase C inhibitor H7, while exposure to DCG IV, a group II metabotropic glutamate receptor (mGluR) agonist, resulted in improvement of [ 3 H]‐D‐aspartate uptake and a partial reversal of transporter downregulation. These results are consistent with our recent in vivo findings of a loss of astrocytic glutamate transporters in TD and provide evidence that TD conditions may increase phosphorylation of GLAST, contributing to its downregulation. In addition, manipulation of group II mGluR activity may provide an important strategy in the treatment of this disorder. © 2003 Wiley‐Liss, Inc.