Abstract
Purpose: :
To study the role of caspases in apoptosis of photoreceptor cells in inherited retinal degeneration of the Royal College of Surgeons (RCS) rats.
Methods: :
RCS dystrophic rats were raised in dim–cyclic light. At postnatal days 27 (P27), they were divided into 4 groups. They were uninjected or injected with 2 µl of DMSO 2%, Z–VAD–FMK (inhibiting caspase–1, –3, –4 and –7; 1.06 mM in DMSO 2%) or Y–VAD–FMK (inhibiting caspase–1 and –4; 0.16 mM in DMSO 2%). Seven days later, at P35, electroretinograms (ERGs) were recorded to obtain the b–wave sensitivities curves. These curves were fitted to calculate the maximal b–wave amplitude (Bmax). After ERGs, rats were sacrificed for morphometric analysis and apoptotic nuclei detection (Apoptag kit). The Outer Nuclear Layer (ONL) thickness was measured from the inferior ora serata to the superior ora serata every 0.18 mm and areas under the ONL thicknesses curves were calculated. Apoptotic cell nuclei were counted under microscope.
Results: :
At P35, Bmax of Z–VAD–FMK (510 ± 95 µV) and Y–VAD–FMK (556 ± 112 µV) injected groups are significantly higher (p< 0,02) than the untreated (368 ± 61 µV) or DMSO (220 ± 168 µV) injected groups, these two last groups being not significantly different from each other. In the same way, Y–VAD–FMK and Z–VAD–FMK treated groups have significantly (p<0.01) higher areas under the ONL thickness curves than the untreated or DMSO injected groups. In addition, ONL area of Y–VAD–FMK treated group is significantly more preserved than Z–VAD–FMK group by 8 % in the superior side (p<0.03) and 27 % in the inferior side of the retina (p<0.0001). Significantly more apoptotic nuclei were observed in the ONL of the untreated or DMSO groups than in the caspases inhibitors treated groups.
Conclusions: :
The injections of Z–VAD–FMK and Y–VAD–FMK have preserved the retinal structure and function of the RCS rats suggesting a caspase–dependent mechanism in this model of photoreceptor degeneration. In addition, better protective effect by Y–VAD–FMK indicated a strong implication of caspase–1 and/or –4 in the apoptotic cascade. Further experiments are on course to better elucidate the caspase activation in inherited retinal degeneration of the RCS rats.
Keywords: retinal degenerations: cell biology • apoptosis/cell death • neuroprotection