Glutathione peromidase-1 deficiency leads to increased nuclear light scattering, membrane damage, and cataract formation in gene-knockout mice

PURPOSE. Previous in vitro studies with transgenic and gene-knockout mice h ave shown that lenses with elevated levels of glutathione peroxidase (CP-X) -1 activity are able to resist the cytotoxic effect of H2O2, compared with normal lenses and lenses from GPX-1-deficient animals. The purpose of this study was to investigate the functional role of this enzyme in antioxidant mechanisms of lens in vivo by comparing lens changes of gene-knockout mice with age-matched control animals. METHODS. In vivo lens changes were monitored by slit lamp biomicroscopy, an d enucleated lenses were examined under a stereomicroscope in gene-knockout animals and age-matched control animals ranging in age from 3 weeks to 18 months. Transmission (TEM) and confocal microscopy were performed on differ ent regions of lenses after the mice were killed at various times. RESULTS. Slit lamp images showed an increase in nuclear light scattering (N LS) in gene-knockout mice compared with control animals. TEM revealed chang es in the nucleus as early as 3 weeks of age by the appearance of waviness of fiber membranes. With increasing age, there was greater distortion of fi ber membranes and distension of interfiber space at the apex of fiber cells compared with control mice. The changes in nuclear fiber membranes were ev en more dramatic, as observed by confocal microscopy, which was performed o n thicker sections. In contrast to the changes in the lens nucleus, the mor phology of the epithelium and superficial cortex remained unchanged in knoc kout animals during the same experimental period, consistent with slit lamp observations, Stereomicroscopy of ex vivo lenses demonstrated a significan t increase in opacification in gene-knockout mice relative to control anima ls of the same age. This effect became evident in mice aged 5 to 9.9 months and persisted thereafter in older animals, resulting in mature cataracts a fter 15 months. CONCLUSIONS. The results demonstrate the critical role of GPX-1 in antioxid ant defense mechanisms of the lens nucleus. The increased NLS appears to be associated with damage to fiber membranes in the nucleus, which is particu larly susceptible to oxidative challenge because of the deficiency of GPX-1 . It is suggested that the lens membrane changes in the knockout animals ma y be due to the formation of lipid peroxides, which serve as substrates for GPX-1. Cataract development in gene-knockout mice appeared to progress fro m focal opacities, apparent at an earlier age, to lamellar cataracts betwee n 6 and 10 months, and finally to complete opacification in animals older t han 15 months. This is the first reported phenotype in GPX-1-knockout mice.