Abstract
Abstract: :
Purpose: To study the involvement of caspase proteases in light–induced retinal degeneration in rats. Methods: Wistar rats were raised in dim–cyclic light. At 45 days old they were dark–adapted overnight before being exposed for 24 hours to a 3400 lux light. They were uninjected, stung intravitreally, or injected 16 hours before exposure to the damaging light with PBS1X, DMSO 2%, caspase inhibitor Z–VAD–FMK (inhibiting caspase–1, –3, –4 and –7, 1,06 mM) or caspase inhibitor Y–VAD–FMK (inhibiting caspase–1 and –4, 0,16 mM). The maximal b–wave amplitude (Bmax) was derivated from the electroretinograms recorded before exposure and/or treatment, at 1 day (D1) and 15 days (D15) after exposure to the damaging light. Rats were sacrificed at D1 and D15 for morphometric analysis and/or detection of apoptotic nuclei (TUNEL method). Unexposed animals were processed in parallel. Caspase–1 and –3 activities were assayed at 0h, 6h, 12h, 24h of light–exposure and at D1. Results: In the untreated group, light–exposure induced a reduction by 75% of Bmax, 50% of the outer nuclear layer thickness (ONL) and a 60 times increase of TUNEL–labelled cells in the ONL, at D1. At D15, there was a further reduction of ONL by 91%. To sting or to inject PBS, DMSO or Y–VAD–FMK did not protect the retinal function or structure against retinal light damage. But, in Z–VAD–FMK injected–exposed rat retinas, Bmax and ONL were preserved to 81% and 84%, respectively and there was 3 times less apoptotic nuclei at D1 in the ONL compared to the uninjected–exposed rats. Compared to the unexposed retinas, caspase–1 activity was significantly increased by 51% at D1 in the uninjected–exposed retinas but not in the Z–VAD–FMK injected–exposed ones. Caspase–3 activity did not vary during or after exposure to the damaging light. Conclusions: In our light–induced retinal degeneration model like in others models, photoreceptors die by apoptosis. Z–VAD–FMK, a large broad spectrum caspase inhibitor, was effective in the reduction of light–induced retinal apoptosis suggesting a caspase–dependent mechanism. Caspase–3 was not implicated and caspase–1 activity increased only after the damaging light was turned off. The lack of protection by Y–VAD–FMK (caspase–1 and –4 inhibitor) could be due to a too low concentration or a too early injection. Further experiments are on course to better understand the caspase activation in our model of retinal light degeneration.
Keywords: retinal degenerations: cell biology • cell death/apoptosis • electroretinography: non-clinical