Potential role for astroglial D-amino acid oxidase in extracellular D-serine metabolism and cytotoxicity

J Biochem. 2006 Feb;139(2):295-304. doi: 10.1093/jb/mvj036.

Abstract

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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acids / pharmacology
  • Animals
  • Apoptosis / drug effects*
  • Astrocytes / drug effects
  • Astrocytes / enzymology*
  • Catalysis
  • Cell Line
  • Cell Survival / drug effects
  • Cells, Cultured
  • Chlorpromazine / pharmacology
  • D-Amino-Acid Oxidase / antagonists & inhibitors
  • D-Amino-Acid Oxidase / chemistry
  • D-Amino-Acid Oxidase / physiology*
  • Dose-Response Relationship, Drug
  • Enzyme Activation / drug effects
  • Enzyme Inhibitors / pharmacology
  • Extracellular Space / metabolism
  • Gene Expression Regulation, Enzymologic / drug effects
  • Gene Expression Regulation, Enzymologic / genetics
  • Hydrogen Peroxide / metabolism
  • Hydrogen Peroxide / pharmacology
  • Mice
  • Rats
  • Serine / antagonists & inhibitors
  • Serine / metabolism*
  • Serine / pharmacology*
  • Sodium Benzoate / pharmacology
  • Stereoisomerism

Substances

  • Amino Acids
  • Enzyme Inhibitors
  • Serine
  • Hydrogen Peroxide
  • Dao1 protein, mouse
  • D-Amino-Acid Oxidase
  • Sodium Benzoate
  • Chlorpromazine