EAAT and Xc⁻Exchanger Inhibition Depletes Glutathione in the Transformed Human Lens Epithelial Cell Line SRA 01/04

Abstract

Inhibition of Glu and Cys uptake by EAAT and Xc(-) exchanger antagonists depletes GSH in human lens epithelial cells. These in vitro results support pivotal roles for EAAT and Xc(-) exchanger activities in maintaining GSH and protection against oxidative stress in cortical lens epithelium.

Early Onset of Age-Related Cataracts in Cystine/Glutamate Antiporter Knockout Mice

“…4,5,24,32 A number of alternative pathways exist in the lens that may be utilized to maintain GSH levels in the absence of xCT. For example, it is known that the lens contains the molecular machinery to take up cysteine directly via cysteine uptake transporters, 14,[17][18][19]33 synthesize cysteine via the transsulfuration pathway, 34 or directly uptake GSH via putative GSH transporters. 35 Together, these alternative mechanisms may be upregulated to compensate for the loss of GSH in the cortex, and may explain why no differences were seen in GSH levels in the cortex and the lens as a whole.…”

“…Because in vitro studies have shown xCT to be important in providing a source of intracellular cyst(e)ine for GSH synthesis, 14,17 we next investigated whether loss of xCT results in change in intracellular GSH levels in the lens (Fig. 8).…”

“…3 xCT is also expressed in different tissues of the eye, such as the cornea (rat, mouse, and human), the ciliary body (rat and mouse), the lens (rat, mouse, canine, and human), and the retina (rat, mouse, and human). [12][13][14][15][16][17][18][19][20][21][22] In cultured human corneal epithelial cells, retinal pigment epithelial cells, and lens epithelial cells, pharmacological inhibition of xCT has been shown to result in reduced glutathione (GSH) depletion, pointing to a role for xCT in maintaining GSH levels in these cells. 14,16,17 Localization studies of xCT in the rat and human cornea also indicate a role for xCT in GSH synthesis, 21,23 while co-localization of xCT to the synaptic ribbon complex in the rat retina suggests a role for xCT in glutamate neurotransmission.…”

Identification, Expression, and Roles of the Cystine/Glutamate Antiporter in Ocular Tissues

“…Since xCT appears to be expressed in the different tissues of the eye, a number of different methods have been used to evaluate the function of xCT in ocular tissues. This has been achieved through pharmacological inhibition of xCT by (S)-4-carboxyphenylglycine or L-glutamate, modulating xCT activity using elevated exogenous cystine [10,34,44,46], or the use of an xCT KO mouse [35]. Table 3 provides a summary of in vivo and in vitro studies conducted to test the function of xCT in ocular tissues, alongside other tissues of the body.…”

“…A study using human lens epithelial cells showed that inhibition of xCT by L-glutamate resulted in depletion of cysteine levels by 52% and depletion of GSH by 28% [46]. However, in whole lenses, the levels of cystine and cysteine were similar between WT and xCT KO mice [35].…”