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H. Wang, J. Gao, X. Sun, K. Varadaraj, M. Farrell, V. N. Reddy, R. T. Mathias; The Lens’ Circulation in 14-Month-Old GPX-1 KO and WT Mice. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4218.
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Knockout (KO) of Glutathione Peroxidase-1 (GPX-1) provides a useful model to study long term effects of H2O2 when an important protective mechanism is absent. GPX-1 KO mice get an age related nuclear cataract. We previously reported results on gap junction coupling and [Ca2+]i in lenses from 2 month old GPX-1 KO and WT mice. We have extended this study to include fiber cell membrane water permeability pf, [Na+]i and to 14-month-old mice.
Impedance studies of gap junction coupling were performed in intact lenses. [Ca2+]i was measured by injecting the Ca2+-sensitive dye FURA2 into lens fiber cells. [Na+]i was similarly measured using the Na+-sensitive dye SBFI. Fiber cell membrane vesicle swelling in hypertonic medium was used to determine pf.
At 2 months of age, all lenses were transparent. In WT lenses, pf (µm/s) was 35±3, the outer differentiating fiber gap junction coupling conductance GDF (S/cm2) was 1.04±.07, and the inner mature fiber coupling conductance GMF (S/cm2) was 0.42±.08. At 14 months of age, almost all GPX-1 KO mice developed a cataract, but the same age control lenses were transparent. The pf was 28±4 for WT vs 8±3 for KO. GDF was 0.46±0.04 for WT vs 0.23±0.03 for KO; GMF was 0.13±0.02 for WT vs 0.04±0.004 for KO. Lenses from 14-month-old WT mice showed a large accumulation of [Na+]i relative to young lenses, however the data fell on a smooth diffusion curve suggesting the circulation was still functional. For the GPX-1 KO data, there was clear loss of the circulation in central cells as [Na+]i accumulated beyond that predicted for diffusion. [Ca2+]i in the lens core of both 14-month-old WT and KO mice was significantly higher than in young lenses, and the GPX-1 KO data deviated significantly from the prediction for a normal circulation, suggesting loss of calcium homeostasis.
All lenses are subjected to cumulative oxidative damage that causes significant reductions in gap junction coupling and some loss of pf. Knockout of GPX-1 increased the damage and caused age onset nuclear cataracts. Our model is that reductions in coupling disrupt the lens circulation. This disruption leads to Ca2+ accumulation, which activates Ca-dependent proteases and the resulting proteolysis causes the central opacity.
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