Tracy K Van Ells

Georgia Health Sciences University, Augusta, Georgia, United States

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Publications (3)8.61 Total impact

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    ABSTRACT: The cystine-glutamate exchanger, system x(c)(-), mediates the Na(+)-independent exchange of cystine into cells, coupled to the efflux of intracellular glutamate. System x(c)(-) plays a critical role in glutathione homeostasis. Early studies of brain suggested that system x(c)(-) was present primarily in astrocytes but not neurons. More recent work indicates that certain brain neurons have an active system x(c)(-). In the retina, system x(c)(-) has been demonstrated in Müller and retinal pigment epithelial cells. We have recently suggested that two protein components of system x(c)(-), xCT and 4F2hc, are present in ganglion cells of the intact retina. Here, we have used (1) molecular and immunohistochemical assays to determine whether system x(c)(-) is present in primary ganglion cells isolated from neonatal mouse retinas and (2) functional assays to determine whether its activity is regulated by oxidative stress in a retinal ganglion cell line (RGC-5). Primary mouse ganglion cells and RGC-5 cells express xCT and 4F2hc. RGC-5 cells take up [(3)H]glutamate in the absence of Na(+), and this uptake is blocked by known substrates of system x(c)(-) (glutamate, cysteine, cystine, quisqualic acid). Treatment of RGC-5 cells with NO and reactive oxygen species donors leads to increased activity of system x(c)(-) associated with an increase in the maximal velocity of the transporter with no significant change in the substrate affinity. This is the first report of system x(c)(-) in primary retinal ganglion cells and RGC-5 cells. Oxidative stress upregulates this transport system in RGC-5 cells, and the process is associated with an increase in xCT mRNA and protein but no change in 4F2hc mRNA or protein.
    No preview · Article · Jun 2006 · Cell and Tissue Research
  • Hany Naggar · Tracy K Van Ells · Vadivel Ganapathy · Sylvia B Smith
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    ABSTRACT: Reduced-folate transporter-1 (RFT-1), a typical transport protein with 12 membrane-spanning domains, transports reduced-folates, such as N5-methyltetrahydrofolate (MTF), the predominant circulating form of folate. RFT-1 is localized to the RPE apical membrane and transports folate from RPE to photoreceptor cells. We asked whether RFT-1 activity in RPE is altered under high folate conditions. ARPE-19 cells were cultured 24, 48, or 72 h in medium containing either 0.5 nM, 5.0 nM, or 2.26 microM MTF, and the activity of RFT-1 was assessed by determining the uptake of N5-MTF. Semiquantitative reverse transcription-polymerase chain reaction and Western blot analysis were used to study RFT-1 gene and protein expression. Cells treated for 72 h with 2.26 microM MTF showed a significant (40%) decrease in MTF uptake compared to cells exposed to 0.5 nM or 5 nM MTF. The effect of high concentrations of folate on RFT-1 activity was specific. Kinetic analysis showed that folate-induced attenuation of RFT-1 activity was associated with a decrease in the maximal velocity of the transporter, but no change in the substrate affinity. Steady-state levels of RFT-1 mRNA and protein decreased significantly in the presence of excess folate. Excess folate levels downregulate RFT-1 in RPE. This study represents the first molecular analysis of the regulation of RFT-1 by folate in RPE and reveals attenuation of the activity and expression of a folate transport protein under conditions of high levels of folate.
    No preview · Article · Feb 2005 · Current Eye Research
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    ABSTRACT: Neuronal cell death has been reported in retinas of humans with diabetic retinopathy and in diabetic rat models. Little is known about neuronal cell death in mouse models of diabetic retinopathy. This study was designed to determine whether neurons are lost in diabetic mouse retinas and whether the loss involves an apoptotic process. Three-week-old C57Bl/6 mice were made diabetic with streptozotocin. They were studied over the course of 14 weeks after onset of diabetes. Eyes were processed for morphometric analysis and detection of apoptotic cells by TUNEL analysis and activated caspase-3 and were subjected to electron microscopy. Morphometric analysis of retinal cross sections of mice that had been diabetic 14 weeks showed approximately 20% to 25% fewer cells in the ganglion cell layer compared with age-matched control mice. There was a modest, but significant, decrease in the thickness of the whole retina and the inner and outer nuclear layers in mice that had been diabetic for 10 weeks. TUNEL analysis and detection of active caspase-3 revealed that cells of the ganglion cell layer were dying by apoptosis. Electron microscopic analysis detected morphologic features characteristic of apoptosis, including margination of chromatin and crenated nuclei of cells in the ganglion cell layer. The data suggest that in diabetic mouse retinas, neurons in the ganglion cell layer die, and this death occurs through an apoptotic pathway. Diabetic mice may be appropriate and valuable models for studies of neuronal cell death in diabetes.
    No preview · Article · Oct 2004 · Investigative Ophthalmology & Visual Science

Publication Stats

316 Citations
8.61 Total Impact Points


  • 2004-2006
    • Georgia Health Sciences University
      • Department of Cellular Biology & Anatomy
      Augusta, Georgia, United States