Photo-oxidative stress down-modulates the activity of nuclear factor-kappaB via involvement of caspase-1, leading to apoptosis of photoreceptor cells

The mechanisms of photoreceptor cell death via apoptosis, in retinal dystro phies, are largely not understood. In the present report we show that visib le light exposure of mouse cultured 661W photoreceptor cells at 4.5 milliwa tt/cm(2) caused a significant increase in oxidative damage of 661W cells, l eading to apoptosis of these cells. These cells show constitutive expressio n of nuclear factor-kappa B (NF-kappa B), and light exposure of photorecept or cells results in lowering of NF-kappa B levels in both the nuclear and c ytosolic fractions in a time-dependent manner. Immunoblot analysis of I kap pa B alpha and p50, and p65 (RelA) subunits of NF-kappa B, suggested that p hoto-oxidative stress results in their depletion. Immunocytochemical studie s using antibody to RelA subunit of NF-kappa B further revealed the presenc e of this subunit constitutively both in the nucleus and cytoplasm of the 6 61W cells. Upon exposure to photo-oxidative stress, a depletion of the cyto plasmic and nuclear RelA subunit was observed. The depletion of NF-kappa B appears to be mediated through involvement of caspase-1, Furthermore, trans fection of these cells with a dominant negative mutant I kappa B alpha grea tly enhanced the kinetics of down modulation of NF-kappa B, resulting in a faster photo-oxidative stress-induced apoptosis. Taken together, these stud ies show that the presence of NF-kappa B RelA subunit in the nucleus is ess ential for protection of photoreceptor cells against apoptosis mediated by an oxidative pathway.