Maintenance of Neuronal Glutathione by Glial Cells

Abstract

Glutathione levels in neurons and glial cells were investigated in a neuronal-glial coculture and in separate cultures. Brain cell suspensions obtained from cerebral hemispheres of fetal rats were cultured, and after 5 days the glutathione content of this cell population, consisting mainly of neurons and astroglial cells, was 23.0 nmol/mg of cell protein, with a significantly high content in glial cells (28.0 nmol/mg of protein) in comparison with neurons (18.8 nmol/mg of protein). When the neurons and glial cells were separated and recultured in fresh medium, neuronal glutathione rapidly decreased, whereas glial glutathione remained unchanged. Cysteine is a rate-limiting precursor for glutathione synthesis, and its level was also decreased in neurons, but not in glial cells. Cysteine was taken up rapidly by both neurons and glial cells, but cystine was taken up only by glial cells. This accounts for the rapid decrease of glutathione in the cultured neurons, because the culture medium contains cystine, but not cysteine. It was also found that the cultured glial cells released cysteine into the medium. These results suggest that neurons maintain their glutathione level by taking up cysteine provided by glial cells.

Thimerosal Neurotoxicity is Associated with Glutathione Depletion: Protection with Glutathione Precursors

“…Both NAC and glutathione ethyl ester provided significant protection against cell death whereas cystine and methionine were without effect. The lack of effect of cystine is consistent with previous reports that neurons can take up cysteine, but not cystine (Sagara et al, 1993). As expected, methionine afforded no protection.…”

“…Glutathione ethyl ester is an esterified form of glutathione that is able to cross the cell membrane against the concentration gradient (Anderson et al, 2004). Cystine is the disulfide (oxidized) form of cysteine that is readily taken up by astrocytes, but not neurons (Sagara et al, 1993). Since astrocytes are unable to synthesize GSH from methionine, the addition of methionine to the media served as a negative control.…”

Searching for Mechanisms of N-Methyl-d-Aspartate-Induced Glutathione Efflux in Organotypic Hippocampal Cultures

“…Alternatively, the efflux have different cellular origin. Glutathione is present in both neurons and glia (29,30,(82)(83)(84)(85)(86), but as no functional NMDA receptors appear to be located on hippocampal glia cells (87), the most straightforward explanation for the increase in glutathione efflux is neuronal release. However, it cannot be excluded that NMDA-receptor stimulation induces a release of a substance from neurons that evokes glutathione release from the glial cells.…”

“…Glutathione may also increase NMDA receptor responses by interacting with its redox sites (26)(27)(28). Furthermore, because the breakdown products of glutathione include cysteine, glycine, and cysteineglycine, extracellular breakdown may supply surrounding cells with these glutathione precursors (29)(30)(31). Despite the key function of glutathione in intracellular redox regulation and the putative extracellular effects in brain, the mechanisms and factors determining the efflux remain unknown.…”

Regulation of Neuronal Glutathione Synthesis

“…The dipeptide CysGly is hydrolyzed by neuronal dipeptidase into cysteine and glycine (42,60). Neurons utilize cysteine but not cystine for GSH synthesis, whereas glial cells utilize both (43,54). The CSF cysteine concentration was much higher than that of cystine (56).…”