Mouse models of accelerated lenticular aging by carbonyl and oxidant stress

Purpose Age-related human cataracts form as a result combined of carbonyl and oxidant stress and other crystallin modifications that destabilize their chaperone function. However, without appropriate models it has been very difficult to demonstrate cause-and effect and implicate protein modifications in the disease process. To test the role of vitamin C oxidation products (carbonyl stress) and protein oxidation in the formation of crystallin aggregates, we have generated two types of mice that exhibit rapid protein damage. Methods The first model of increased carbonyl stress is the hSVCT2 mouse in which we overexpressed the human vitamin C two transporter under control of the mouse alphaB-crystallin promoter. (Fan et al. PNAS 2006). The second model of increased protein oxidation is the LEGSKO (Lens Glutathione Synthesis Conditional Knockout mouse) in which we conditionally knocked out gamma-glutamyl cysteine ligase (Gclc) in order to mimic the low GSH levels of the old lens nucleus. Results Gamma glutamyl cysteine ligase mRNA, activity and glutathione (GSH) levels are severely depressed in the lens of the homozygous mouse, but not in the heterozygous mouse. GSSG/GSH ratio, methionine oxidation and protein disulfide formation are increased at 6 mos of age. Nuclear opacities turn into full nuclear cataracts at 6 mos. Protein disulfide formation reveals a shift from intra- to interdisulfide bonds similar to aging human lens. Dramatic upregulation of several candidate transporters is noted. Conclusion Availability of two mice strains with increased carbonyl and oxidative stress, respectively, will allow us to test the hypothesis that rapid modification of crystallins predisposes to protein aggregation and cataractogenesis when bred together. It will also help us develop drugs that slow down the progression of cataractogenesis and study molecular events that precede cataract formation.