Mapping of the cystine–glutamate exchanger in the mouse eye: a role for xCT in controlling extracellular redox balance
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The cystine–glutamate exchanger (system xc−) is responsible for the exchange of extracellular cystine for intracellular glutamate. In this study, we mapped the expression of xCT, the light chain subunit of system xc− in the different tissues of 3–6-week-old mouse (C57BL/6J) eye and have used an xCT knockout mouse to verify labelling specificity. Moreover, using the xCT knockout mouse, we investigated whether xCT was involved in maintaining extracellular redox balance in the eye. xCT transcript and protein were present in the cornea, lens and retina of wild-type mice, but not knockout mice. xCT was localised to the corneal epithelium, and the lens epithelium and cortical fibre cells but was absent in the iris. xCT localisation could not be determined in the ciliary body or retina, since xCT labelling was also detected in the knockout indicating a lack of specificity of the xCT antibody in tissues of a neural origin. Intracellular cysteine and cystine concentrations were similar in the wild-type and xCT knockout mouse for the cornea, lens, and retina. While extracellular cysteine levels were similar between the plasma, aqueous humour, and vitreous humour of the wild-type and xCT knockout mouse, extracellular cystine levels in the plasma and aqueous were significantly elevated in the xCT knockout mouse relative to the wild type. This suggests that loss of xCT results in an increased oxidative environment, particularly within the anterior chamber of the eye in which the aqueous humour resides. How this oxidative shift impacts ocular tissues that interface with the aqueous humour over time will be the focus of future work.
KeywordsCystine/glutamate exchanger Ocular tissues Redox balance Oxidative stress
The researchers wish to acknowledge funding from Auckland Medical Research Fund, the Faculty Research Development Fund from the University of Auckland, the Maurice and Phyllis Paykel Trust, the New Zealand Optometric Vision Research Foundation, the Hope Foundation for Research on Ageing and the New Zealand Association of Optometrists. In addition, we would also like to thank Professor Hideyo Sato for providing us with the xCT KO mice, Associate Professor Robb de Iongh for the mouse embryos, and Ms Satya Amirapu for her assistance with paraffin embedding of P3 lenses and sectioning and deparaffinising of the P3 and E16 tissues.
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