Visualising the activity of the cystine‐glutamate antiporter in glial cells using antibodies to aminoadipic acid, a selectively transported substrate

Abstract

The cystine-glutamate antiporter is a transport system that facilitates the uptake of cystine, concomitant with the release of glutamate. The cystine accumulated by this transporter is generally considered for use in the formation of the cysteine-containing antioxidant glutathione, which is abundant in many glial cells. This study used the simple strategy of generating an antibody to aminoadipic acid, a selective substrate for the cystine-glutamate antiporter. Stereospecific accumulation of aminoadipic acid into specific cell types in rat brain slice preparations was detected immunocytochemically. Strong accumulation was detected in astroglial cells in all brain regions studied including those in white matter tracts. Strong accumulation into radial glial cells, including the retinal Müller cells and the Bergmann glial cells was also observed. Glial accumulation was observed not only in cells within the blood brain barrier, but also outside such; anterior pituitary folliculostellate cell and intermediate lobe pituitary glial cells exhibited strong accumulation of aminoadipic acid. Interestingly, some glial cells such as the posterior pituitary glial cells (pituicytes) exhibited very little if any accumulation of aminoadipic acid. Within the brain labelling was not uniform. Particularly strong labelling was noted in some regions, such as the glial cells surrounding the CA1 pyramidal cells. By contrast, neurons never exhibited uptake of aminoadipic acid. Because cystine uptake is associated with glutamate release, it is suggested that this antiporter might contribute to release of glutamate from glial cells under some pathophysiological conditions.

Expression of the cystine-glutamate exchanger (xc −) in retinal ganglion cells and regulation by nitric oxide and oxidative stress

“…Work by Kato in the early 1990's [13] described system x cexpression in Müller cells, the predominant glial cell of the retina. These findings were confirmed by Pow in 2001 [14] using an antibody against aminoadipic acid, which is a selectively transported substrate for system x c -. System x c -has been studied extensively at the functional and molecular level in Müller cells [15] and also in retinal endothelial cells [7,8].…”

Contributions of astrocytes and CO to pial arteriolar dilation to glutamate in newborn pigs

“…Injury to the superficial cortical glia limitans under the cranial window was produced by treatment with the selective glia toxin L-2-␣-aminoadipic acid (L-AAA) (24,55,56). The high cellular specificity of L-AAA apparently results from the rapid uptake of the toxin by the cystine-glutamate antiporter expressed by glia and not other brain cells (16,47). The precise mechanism of injury remains uncertain.…”

Regulation of Neuronal Glutathione Synthesis

“…Cystine is taken up into the cell in exchange for glutamate via system xc-, which can be inhibited by a high extracellular glutamate concentration (62). System xc-is present on astrocytes, microglia, retinal Muller cells, and Bergmann glial cells in the cerebellum (63,64). Neurons reportedly could not utilize cystine adequately for their own GSH synthesis (43,54,56), and cystine uptake activity was especially important for maintaining the GSH level in astrocytes (43).…”