INDUCTION OF HEME OXYGENASE-1 IN THE RETINA BY INTENSE VISIBLE-LIGHT - SUPPRESSION BY THE ANTIOXIDANT DIMETHYLTHIOUREA

The effect of intense visible light (light damage) on the expression o f heme oxygenase 1 (HO-1), a protein induced by oxidative stress, was investigated in the rat retina. A sensitive reverse transcription-PCR assay demonstrated the expression of mRNA for HO-1 as well as HO-2, th e noninducible HO form, in the normal retina, As analyzed by Northern blotting, however, HO-1 mRNA was barely detectable under normal circum stances, After exposure to intense visible light, retinas had markedly higher HO-1 mRNA levels than unexposed controls, with increases up to 52- and 98-fold at 12 and 24 hr of exposure, respectively Intense lig ht exposure also resulted in an increase in HO-1 protein, In contrast, no appreciable change in HO-2 mRNA or protein was observed, The incre ase in HO-1 message was more pronounced in rats previously reared in t he dark than in those reared in a weak cyclic-light environment. A mar ked decrease from the high level of HO-1 mRNA induced by light insult was observed when the animals were allowed to recover in the dark for 24 hr after light exposure, Most important, treatment of animals with 1,3-dimethylthiourea, a synthetic antioxidant, prior to light exposure effectively blocked the increase in HO-1 mRNA, Thus, HO-1 is a sensit ive marker for assessing light-induced insult in the retina, Since inc reased expression of HO-1 is thought to be a cellular defense against oxidative damage, its expression may play an important role in protect ing the retina against tight damage.