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Martis RM, Li B, Donaldson PJ, Lim JCH. Early Onset of Age-Related Cataracts in Cystine/Glutamate Antiporter Knockout Mice. Invest Ophthalmol Vis Sci 2021; 62:23. [PMID: 34156426 PMCID: PMC8237109 DOI: 10.1167/iovs.62.7.23] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Purpose The purpose of this study was to determine the importance of the xCT is a subunit. The cystine/glutamate antiporter is actually system xc-xCT subunit of the cystine/glutamate antiporter in maintaining redox balance by investigating the effects of the loss of xCT on lens transparency and cystine/cysteine balance in the aqueous humour. Methods C57Bl/6 wild-type and xCT knockout mice at five age groups (6 weeks to 12 months) were used. Lens transparency was examined using a slit-lamp and morphological changes visualized by immunolabelling and confocal microscopy. Quantification of glutathione in lenses and cysteine and cystine levels in the aqueous was conducted by liquid chromatography tandem mass spectrometry (LC-MS/MS). Results Slit-lamp examinations revealed that 3-month-old wild-type mice and xCT knockout mice lenses exhibited an anterior localized cataract. The frequency of this cataract significantly increased in the knockout mice compared to the wild-type mice. Morphological studies revealed a localized swelling of the lens fiber cells at the anterior pole. Glutathione levels in whole lenses were similar between wild-type and knockout mice. However, glutathione levels were significantly decreased at 3 months in the knockout mice in the lens epithelium compared to the wild-type mice. Aqueous cysteine levels remained similar between wild-type and knockout mice at all age groups, whereas cystine levels were significantly increased in 3-, 9-, and 12-month-old knockout mice compared to wild-type mice. Conclusions Loss of xCT resulted in the depletion of glutathione in the epithelium and an oxidative shift in the cysteine/cystine ratio of the aqueous. Together, these oxidative changes may contribute to the accelerated development of an anterior cataract in knockout mice, which appears to be a normal feature of aging in wild-type mice.
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Affiliation(s)
- Renita Maria Martis
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand.,New Zealand National Eye Centre, University of Auckland, Auckland, New Zealand
| | - Bo Li
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand.,New Zealand National Eye Centre, University of Auckland, Auckland, New Zealand
| | - Paul James Donaldson
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand.,New Zealand National Eye Centre, University of Auckland, Auckland, New Zealand
| | - Julie Ching-Hsia Lim
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand.,New Zealand National Eye Centre, University of Auckland, Auckland, New Zealand
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Identification, Expression, and Roles of the Cystine/Glutamate Antiporter in Ocular Tissues. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2020; 2020:4594606. [PMID: 32655769 PMCID: PMC7320271 DOI: 10.1155/2020/4594606] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 05/21/2020] [Indexed: 01/21/2023]
Abstract
The cystine/glutamate antiporter (system x c -) is composed of a heavy chain subunit 4F2hc linked by a disulphide bond to a light chain xCT, which exchanges extracellular cystine, the disulphide form of the amino acid cysteine, for intracellular glutamate. In vitro research in the brain, kidney, and liver have shown this antiporter to play a role in minimising oxidative stress by providing a source of intracellular cysteine for the synthesis of the antioxidant glutathione. In vivo studies using the xCT knockout mouse revealed that the plasma cystine/cysteine redox couple was tilted to a more oxidative state demonstrating system xc - to also play a role in maintaining extracellular redox balance by driving a cystine/cysteine redox cycle. In addition, through import of cystine, system xc - also serves to export glutamate into the extracellular space which may influence neurotransmission and glutamate signalling in neural tissues. While changes to system xc - function has been linked to cancer and neurodegenerative disease, there is limited research on the roles of system xc - in the different tissues of the eye, and links between the antiporter, aging, and ocular disease. Hence, this review seeks to consolidate research on system xc - in the cornea, lens, retina, and ocular humours conducted across several species to shed light on the in vitro and in vivo roles of xCT in the eye and highlight the utility of the xCT knockout mouse as a tool to investigate the contribution of xCT to age-related ocular diseases.
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Martis RM, Donaldson PJ, Li B, Middleditch M, Kallingappa PK, Lim JC. Mapping of the cystine-glutamate exchanger in the mouse eye: a role for xCT in controlling extracellular redox balance. Histochem Cell Biol 2019; 152:293-310. [PMID: 31396687 DOI: 10.1007/s00418-019-01805-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/24/2019] [Indexed: 12/13/2022]
Abstract
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.
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Affiliation(s)
- Renita M Martis
- Department of Physiology, School of Medical and Health Sciences, University of Auckland, Auckland, 1023, New Zealand.,School of Medical Sciences, University of Auckland, Auckland, New Zealand.,NZ National Eye Centre, University of Auckland, Auckland, New Zealand
| | - Paul J Donaldson
- Department of Physiology, School of Medical and Health Sciences, University of Auckland, Auckland, 1023, New Zealand.,School of Medical Sciences, University of Auckland, Auckland, New Zealand.,NZ National Eye Centre, University of Auckland, Auckland, New Zealand
| | - Bo Li
- Department of Physiology, School of Medical and Health Sciences, University of Auckland, Auckland, 1023, New Zealand.,School of Medical Sciences, University of Auckland, Auckland, New Zealand.,NZ National Eye Centre, University of Auckland, Auckland, New Zealand
| | - Martin Middleditch
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Prasanna K Kallingappa
- Department of Molecular Medicine and Pathology, University of Auckland, Auckland, New Zealand.,School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Julie C Lim
- Department of Physiology, School of Medical and Health Sciences, University of Auckland, Auckland, 1023, New Zealand. .,School of Medical Sciences, University of Auckland, Auckland, New Zealand. .,NZ National Eye Centre, University of Auckland, Auckland, New Zealand.
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