Involvement of caspase-3 in photoreceptor cell apoptosis induced by in vivo blue light exposure.
OBJECTIVE
To investigate the potential role of caspase-3 in blue light-induced apoptosis in photoreceptor cells.


METHODS
Cyclic light-raised Sprague-Dawley rats were exposed to 400 to 480 nm light for 6 hours at an irradiance of 0.64 W/m(2). The rats were then kept in darkness for recovery and killed at scheduled time points from 0 hours up to 24 hours after exposure to light. The unexposed rats were used as the control. Apoptosis was marked with in situ terminal dUTP nick end labeling (TUNEL). Caspase-3 expression was explored using immunohistochemistry, Western blot analysis, real-time RT-PCR, and enzyme activity assay.


RESULTS
Exposure to blue light resulted in photoreceptor cell apoptosis, mostly in the superior temporal area of the retina. TUNEL-positive cells were highest during 8 to 16 hours of recovery in darkness. Procaspase-3 protein was constitutively expressed in the rat retina and was apparently upregulated after exposure to light, with expression peaking at 8 to 16 hours and subsiding at 24 hours. The upregulation was further supported by enhanced transcription of caspase-3 in the postexposure retina. Meanwhile, increased cleavage of caspase-3 into its active fragments of 17 and 19 kDa was detected after exposure to light, peaking at 16 hours. Activation of caspase-3 was subsequently located in the photoreceptor cells and predominantly in the superior part of the temporal quadrant. This coincided with elevated caspase-3-like activity at 16 hours after exposure to light.


CONCLUSIONS
Procaspase-3 protein is temporally upregulated in the retina after in vivo exposure to blue light, and the upregulation is coupled to activation of caspase-3 and concomitant induction of apoptosis in the photoreceptor cells.
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D053148:Caspase 3; D020169:Caspases / Q000235:genetics / Q000502:physiology*; D003116:Color; D004789:Enzyme Activation; D005260:Female; D010775:Photic Stimulation / Q000379:methods*; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology* / Q000528:radiation effects*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D012333:RNA, Messenger; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases