Abbreviations used: ACM, astrocyte conditioned medium; CSH, cysteine; CSSC, cystine; CSSG, cysteine-glutathione disulfide; DIV, days in vitro; FDNB, 1-fluoro-2,4-dinitrobenzene; γGT, γ-glutamyltranspeptidase; GSH, glutathione; GSSG, glutathione disulfide; MEM, minimum essential medium; NCM, neuron conditioned medium.
Astrocytes Provide Cysteine to Neurons by Releasing Glutathione
Article first published online: 18 JAN 2002
Journal of Neurochemistry
Volume 74, Issue 4, pages 1434–1442, April 2000
How to Cite
Wang, X. F. and Cynader, M. S. (2000), Astrocytes Provide Cysteine to Neurons by Releasing Glutathione. Journal of Neurochemistry, 74: 1434–1442. doi: 10.1046/j.1471-4159.2000.0741434.x
- Issue published online: 18 JAN 2002
- Article first published online: 18 JAN 2002
- Conditioned medium;
- Oxidative stress;
Abstract: Cysteine is the rate-limiting precursor of glutathione synthesis. Evidence suggests that astrocytes can provide cysteine and/or glutathione to neurons. However, it is still unclear how cysteine is released and what the mechanisms of cysteine maintenance by astrocytes entail. In this report, we analyzed cysteine, glutathione, and related compounds in astrocyte conditioned medium using HPLC methods. In addition to cysteine and glutathione, cysteine-glutathione disulfide was found in the conditioned medium. In cystine-free conditioned medium, however, only glutathione was detected. These results suggest that glutathione is released by astrocytes directly and that cysteine is generated from the extracellular thiol/disulfide exchange reaction of cystine and glutathione: glutathione + cystine cysteine + cysteineglutathione disulfide. Conditioned medium from neuronenriched cultures was also assayed in the same way as astrocyte conditioned medium, and no cysteine or glutathione was detected. This shows that neurons cannot themselves provide thiols but instead rely on astrocytes. We analyzed cysteine and related compounds in rat CSF and in plasma of the carotid artery and internal jugular vein. Our results indicate that cystine is transported from blood to the CNS and that the thiol/disulfide exchange reaction occurs in the brain in vivo. Cysteine and glutathione are unstable and oxidized to their disulfide forms under aerobic conditions. Therefore, constant release of glutathione by astrocytes is essential to maintain stable levels of thiols in the CNS.