Hyperbaric oxygen in vivo accelerates the loss of cytoskeletal proteins and MIP26 in guinea pig lens nucleus

Previous studies have shown that treatment of guinea pigs with hyperbaric o xygen (HBO) produces certain changes in the lens nuclei of the animals whic h are typical of those occurring during aging. These include an increase in nuclear light scattering (NLS), elevation in levels of oxidized thiols, lo ss of water-soluble protein and damage to nuclear membranes. The present st udy investigated the effect of HBO-treatment in vivo on lens cytoskeletal p roteins and MIP26 which are also known to undergo alteration with age. Youn g (2-month-old) and old (18-month-old) guinea pigs were treated 15 and 30 t imes with HBO (3 times per week with 2.5 atmospheres of 100% oxygen for 2.5 hr periods). SDS-PAGE and Western blotting showed that HBO-treatment of th e older animals accelerated the age-related loss of five nuclear cytoskelet al proteins including actin, vimentin, ankyrin, alpha-actinin and tubulin, compared to levels present in age-matched controls (effects on spectrin and the beaded filaments were not investigated in this study). Treatment of th e young animals with HBO produced losses which were primarily associated wi th concentrations of the nuclear alpha- and beta-tubulins; these cytoskelet al proteins were observed to be most sensitive to the induced oxidative str ess, and were affected earliest in the study. Disulfide-crosslinking, rathe r than proteolysis, appeared to be the main cause of the HBO-induced cytosk eletal protein loss (elevated levels of calcium, which might have induced p roteolysis, were not found in the experimental nuclei). Loss of MIP26 was o bserved only in the older guinea pigs treated 30 times with HBO; both disul fide-crosslinking and degradation to MIP22 were associated with the disappe arance. Thus, nuclear MIP26 was susceptible to oxidative stress, but less s o than the cytoskeletal proteins, particularly the tubulins. No cortical ef fects on either MIP26 or the cytoskeletal proteins were observed under any of the treatment protocols. No direct link was observed between an HBO-indu ced increase in NLS (observed in both the young and old animals using slit- lamp biomicroscopy) and losses of either MIP26 or the cytoskeletal proteins . The appearance of HBO-induced nuclear opacity without any change in the l evels of nuclear sodium, potassium or calcium is similar to that observed p reviously for human senile pure nuclear cataracts, The results provide addi tional evidence that molecular oxygen can enter the nucleus of the lens and promote age-related events, The observed effects on MIP26 and the cytoskel etal proteins are indicative of an increased level of lens nuclear oxidativ e stress in the HBO model, possibly a precursor to nuclear cataract. (C) 19 99 Academic Press.