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W. Lavery, M. Miller, W. R. Elliott, R. D. Glickman; NF-B and Caspase Cascade Activation in Response to Laser Injury in the Rat Snake Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4480.
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Photic injury to the eye often results in devastating retinal damage, manifesting in three main forms: photochemical, thermal, and photomechanical. This study focuses on thermal damage. The retina’s cellular response to photic injury is incompletely understood. A common cellular response to injury is activation of the transcription factor complex Nuclear Factor - ΚB (NF-ΚB), which may serve as a survival or an apoptotic signal, as well as activation of caspase genes, which serve as apoptotic signals. This study investigates the involvement of these pathways in response to photoreceptor laser injury.
The Great Plains rat snake (Elaphe guttata emoryi) provides an ideal model because it is a vertebrate with an eye containing a high numerical aperture, all-cone retina, and eye with high quality ocular media. An animal use protocol was approved by the Brooks City-Base IACUC. A 5x5 grid of laser lesions, each individual lesion 100 mm in diameter, was produced with a Nd:VO4 laser (532 nm) emitting a 50 mW, 10 msec pulse. Snakes were sacrificed either 6 or 24 hours post-injury. Eyes were fixed, embedded, sectioned, and H&E stained for lesion identification. Immunohistology was used to detect NF-ΚB, Caspase 3, and Caspase 9 activity in the retinas, and imaged with fluorescence microscopy.
Immunohistology revealed photoreceptor-specific activation of NF-ΚB, Caspase 3, and Caspase 9, often co-localized in laser-damaged cells in eyes enucleated 6 hours and 24 hours post laser injury. Lesioned areas revealed punctate staining, which was absent in tissue stained with non-immune serum.
In many cell types, NF-ΚB activation has been associated with survival after exposure to stressors, e.g. ionizing or nonionizing radiation. In this context, our observation that NF-ΚB and the apoptosis markers, Caspase-3 and Caspase-9, are co-localized, indicates that expression of NF-ΚB is likely not a survival factor in laser-injured retinal photoreceptors, and may induce apoptosis. This finding differs from earlier, in vitro studies of generalized light damage, possibly reflecting the severity of the laser injury, as well as different responses of in vitro and in vivo systems. Our findings shed light on the molecular response to laser injury, which may lead to the development of targeted therapies to treat photic injuries.
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