Potential role for astroglial D-amino acid oxidase in extracellular D-serine metabolism and cytotoxicity.
D-amino acid oxidase (DAO) is a flavoenzyme that catalyzes the oxidation of D-amino acids. In the brain, gene expression of DAO is detected in astrocytes. Among the possible substrates of DAO in vivo, D-serine is proposed to be a neuromodulator of the N-methyl-D-aspartate (NMDA) receptor. In a search for the physiological role of DAO in the brain, we investigated the metabolism of extracellular D-serine in glial cells. Here we show that after D-serine treatment, rat primary type-1 astrocytes exhibited increased cell death. In order to enhance the enzyme activity of DAO in cells, we established stable rat C6 glial cells overexpressing mouse DAO designated as C6/DAO. Treatment with a high dose of D-serine led to the production of hydrogen peroxide (H(2)O(2)) followed by apoptosis in C6/DAO cells. Among the amino acids tested, D-serine specifically exhibited a significant cell death-inducing effect. DAO inhibitors, i.e., sodium benzoate and chlorpromazine, partially prevented the death of C6/DAO cells treated with D-serine, indicating the involvement of DAO activity in d-serine metabolism. Overall, we consider that extracellular D-serine can gain access to intracellular DAO, being metabolized to produce H(2)O(2). These results support the proposal that astroglial DAO plays an important role in metabolizing a neuromodulator, D-serine.
Park
Hwan Ki
HK
Department of Gene Regulatorics, The Institute for Enzyme Research, The University of Tokushima, Tokushima 770-8503, Japan.
Shishido
Yuji
Y
Ichise-Shishido
Sayaka
S
Kawazoe
Tomoya
T
Ono
Koji
K
Iwana
Sanae
S
Tomita
Yumiko
Y
Yorita
Kazuko
K
Sakai
Takashi
T
Fukui
Kiyoshi
K
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001253:Astrocytes / Q000187:drug effects / Q000201:enzymology*; D002384:Catalysis; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002746:Chlorpromazine / Q000494:pharmacology; D003605:D-Amino-Acid Oxidase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000235:genetics; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology; D051379:Mice; D051381:Rats; D012694:Serine / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology*; D020160:Sodium Benzoate / Q000494:pharmacology; D013237:Stereoisomerism
D000596:Amino Acids; D004791:Enzyme Inhibitors; D012694:Serine; D006861:Hydrogen Peroxide; C485958:Dao1 protein, mouse; D003605:D-Amino-Acid Oxidase; D020160:Sodium Benzoate; D002746:Chlorpromazine