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Nicholas Chinskey, Qiong Zheng, David Zacks; Calpain Inhibition Following Retinal Detachment: A Way to Prolong Autophagy and Delay Apoptosis. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1804.
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To examine whether calpain inhibition following retinal detachment would prolong autophagy, an intrinsic cell survival mechanism, and result in reduced photoreceptor apoptosis.
Retinal detachments were created in Brown-Norway rats by subretinal injection of 1% hyaluronic acid and simulated in vitro by Fas-receptor activation of 661W cells, a mouse derived cone cell line. Protein levels of LC3 and autophagy related gene 5 (Atg5), both of which are involved in the creation of the autophagosome, were assayed by western blot. Calpain 1, the calpain member responsible for Atg5 cleavage, activity was monitored by alpha-spectrin cleavage and calpain 1 levels. Various calpain inhibitors, including calpeptin, were added either to the subretinal space or cell culture media. Apoptosis was assessed in vitro by caspase 8 activity assays .
Following retinal detachment, there was an increase in Atg5 and LC3-II protein levels that peaked at 3 days and decreased by 7 days post-detachment. Calpain 1 activation peaked at 7 days and was associated with a decrease in autophagy. Calpain inhibition led to increased levels of autophagy, which remained elevated at the 7 day time point. The increased autophagy levels that resulted from calpain inhibition led to decreased levels of caspase 8 and reduced levels of Fas mediated apoptosis.
Visual outcomes for macula-involving retinal detachments are considerably reduced when repair is prolonged beyond 7 days. Our data suggest that calpain activation, which peaks at 7 days post-detachment, is one of the key steps in triggering photoreceptor cells to shift from cell survival to cell death pathways following retinal detachments. Prolonging autophagy through calpain inhibition leads to reduced photoreceptor apoptosis, and may suggest a novel strategy for improving visual outcomes in patients with retinal detachments.
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