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Shreyasi Choudhury, Yang Liu, Abbot F Clark, Iok-Hou Pang; Knockout Of Caspase-7 Protects Against Optic Nerve Crush-Induced Retinal Ganglion Cell Death. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2667.
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Optic nerve (ON) injury is involved in various ocular diseases, such as glaucoma, which leads to apoptotic death of retinal ganglion cells (RGC) and vision loss. Caspases have been previously implicated in glaucoma and RGC death. However, the role of caspase-7, a functionally unique caspase, in ON injury and glaucomatous damage has not been studied. Therefore, the purpose of this study is to evaluate the role of caspase-7 in ON injury-induced RGC apoptosis.
C57BL/6 (Wt) and caspase-7knockout (casp7KO) mice were used for this study. Optic nerve crush (ONC) was performed on left eyes; right eyes served as control. Activation of caspase-7 was assessed by western blot analysis of the isolated retinas of Wt mice at 3h, 6h, 12h, 1d, 3d, and 7d post ONC. Immunohistochemistry was performed to detect the localization of caspase-7 in RGC. RGC survival was determined by counting the RBPMS (RGC marker) labeled cells in flat-mounted retinas of Wt and casp7KO mice at 7d, 14d and 28d post injury. Both Wt and casp7KO mice were subjected to spectral-domain optical coherence tomography (SD-OCT) and scotopic threshold response of electroretinography (STR-ERG) to evaluate the retinal structural and RGC functional changes respectively at 7d, 14d, and 28d post ONC.
Western blot analysis demonstrated that caspase-7 was activated in Wt retina at 12h, 1d, 3d, and 7d post ONC. The number of surviving RGCs was significantly higher (3173±59 cells/mm2, mean±SEM, n=6, p<0.001) in casp7KO retinas when compared to Wt retinas (1693±84cells/mm2) at 28d post ONC. SD-OCT analysis revealed that the thickness of the inner retinal layer (ganglion cell layer, nerve fiber layer, and inner plexiform layer) in casp7KO mice was greater (54±1.1μm, p<0.05) compared to Wt mice (42.3±1.5μm) at 28d post ONC. Most importantly, STR-ERG analysis demonstrated a decline in amplitude in Wt ONC eyes (10.5±1.9μv), whereas the response was significantly higher (20.7±2.3μv, p<0.05) in casp7KO mice even at 28d post injury.
The current study indicates that injury to the ON activates caspase-7 and knockout of caspase-7 protects the inner retinal layer morphology and RGC function after ONC. Thus, caspase-7 appears to play a critical role in ONC-induced RGC death, and inhibition of caspase-7 activity may be a novel therapeutic target for glaucoma and other neurodegenerative diseases of the retina.
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