Decreased retinal neuronal cell death in caspase-1 knockout mice

To determine whether apoptosis of retinal neurons induced by excessive light exposure and ischemia-reperfusion injury is altered in caspase-1 knockout mice.

Eight- to 10-week-old caspase-1 knockout mice (Casp1-/-) and wild-type (WT) mice (C57BL/6) were exposed to diffuse, cool, white fluorescent light of 25,000 lux for 2 h. Other mice were subjected to retinal ischemia by increasing the intraocular pressure to 110 mmHg for 45 min. Electroretinograms (ERGs) were recorded before and after the light exposure. TdT-dUTP terminal nick-end labeling (TUNEL) was performed to identify the apoptotic cells after the insults. The inner retinal thickness was measured to evaluate the retinal injury after the ischemia-reperfusion. Expression of caspase-1 protein was studied by immunohistochemical analysis and Western blotting. Caspase-1-like protease activity was determined by a colorimetric tetrapeptide substrate.

The morphology of the retina and the amplitudes of the a and b waves of the ERGs of Casp1-/- mice did not differ from those of WT mice. After the light exposure, TUNEL-positive cells were observed in the outer nuclear layer of the WT mice retina. The number of TUNEL-positive photoreceptor nuclei after the light exposure, and the number of nuclei in the inner nuclear layer after the ischemia-reperfusion injury, were significantly less in Casp1-/- mice than in WT mice. There were more caspase-1-positive photoreceptor cells in WT mice after the light injury. The inner retinal layer of Casp1-/- mice was significantly thicker in Casp1-/- mice than in WT mice 2 weeks after the ischemic insult.

Retinal neuronal apoptosis was less prominent in Casp1-/- mice after excessive light exposure and ischemia-reperfusion injury. These data indicate that caspase-1 plays a role in retinal neuronal apoptosis.