Abstract
Abstract: :
Purpose: In bright light–induced photoreceptor apoptosis mtDNA is affected first, triggering the upregulation of a repair response involving DNA polymerase γ. nDNA fragmentation follows about 18 hours later, followed by DNA polymerase ß induction, in an attempt to repair damaged nuclear DNA. However, this light–evoked photoreceptor repair is only partially successful. LAU–0901, a PAF receptor antagonist, has been shown to have neuroprotective activity in the retina under our experimental conditions. The purpose of this study is to explore action/s effects of LAU–0901 on the photoreceptor apoptotic pathway. Methods: Sprague Dawley rats, dark–adapted 2d, were light–treated for 5h and returned to darkness (light controls). 2h prior to light exposure, some rats were treated with LAU–0901 (1µl/gr bw, IP). Eyes were collected 6 and 24h after light. Right retinas were analyzed by Western blot for DNA polymerase γ and ß. Left eyes were fixed, cryoprotected, and sectioned for TUNEL labeling. The total number of TUNEL–positive photoreceptor nuclei were counted in sections cut from the superior to the inferior margins of each retina and averaged. Results: LAU–0901 decreased the number of TUNEL–positive photoreceptor nuclei (cells with fragmented DNA) by 70%. Western blot analysis showed a decrease of 66% in light–induced upregulation of DNA polymerase γ in LAU–0901 treated animals compared to others that had not received the drug. Dark controls injected with LAU–0901 showed an upregulation of DNA polymerase γ of 50% over non–treated animals. Conclusions: Treatment with LAU–0901 protects photoreceptors when exposed to bright light. Nuclear DNA fragmentation is considerably reduced. DNA polymerase γ is also decreased in treated animals suggesting that mtDNA is protected. These data suggest that LAU–0901 acts very early in the apoptotic pathway, probably at the mitochondrial level. It is also possible that LAU–0901 selectively upregulates DNA polymerase γ. As a result, mitochondrial function is preserved and photoreceptor survival is enhanced. (LAU–0901 patent assignee LSUHSC)
Keywords: neuroprotection • mitochondria • photoreceptors