Cataract formation in transgenic HO-1 G143H mutant mice: Involvement of oxidative stress and endoplasmic reticulum stress.

Oxidative stress and endoplasmic reticulum (ER) stress are the key contributing factors for cataract progression. In our previous studies, we demonstrated that the nuclear factor erythroid 2-like-2 (Nrf-2)/heme oxygenase-1 (HO-1)/carbon monoxide (CO) axis protects lens epithelial cells (LECs) against oxidants and ER stress. In the present study, transgenic FVB/N mice overexpressing the negative dominant mutant HO-1 G143H (TgHO-1 G143H) were generated to evaluate the crosstalk among HO-1, oxidative stress and ER stress in maintaining lens transparency. Slit-lamp examination revealed that nuclear cataracts occurred at 4 months in the TgHO-1 G143H mice, which was 5 months earlier than that of the control mice. The lenses of the transgenic mice showed an accumulation of malondialdehyde and protein carbonyl with a decrease in glutathione and protein sulfhydryl levels. Elevated concentrations of ER stress biomarkers (Bip, PERK, ATF6, IRE1, CHOP, caspase-12 and caspase-3) in the lenses of the TgHO-1 G143H mice were identified by western blotting. Furthermore, we confirmed that overexpressed HO-1 G143H in LECs resulted in oxidative insult and apoptosis in vitro. All of these data suggested that HO-1 enzymatic activity loss induces early-onset nuclear cataracts by activating oxidative stress and ER stress.