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J. M. Calandria, P. Mukherjee, N. G. Bazan; Extended Glutamine Tract Protein Expression in Rpe Cells Induces Proteotoxic-Stress and Apoptosis That Is Prevented by Neuroprotectin D1. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5960.
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© ARVO (1962-2015); The Authors (2016-present)
Neurodegenerative diseases share as a common feature the inability of cells to scavenge structurally-damaged or abnormal proteins. The pathogenesis of polyglutamine (polyQ) diseases involves increased protein misfolding and formation of nuclear aggregates, which contain ubiquitin and chaperon proteins. In SCA, not only is the brain affected, but the retina undergoes degeneration as well. It was previously shown that NPD1 synthesis is enhanced by oxidative stress signals to activate pro-survival processes via regulation of gene expression and other cellular processes. We hypothesized that misfolding protein stress induces synthesis of NPD1 and that this lipid mediator promotes cell survival.
We used human RPE primary culture, ARPE-19 cells that express 15-LOX-1 shRNA, as cellular model to assess the stress occurring due to the expression of polyQ protein to determine whether NPD1 acts to prevent apoptosis. Immunostaining and gene reporter assay was used to determine induction of apoptotic and inflammatory signaling by the mutant forms of Ataxin-1 and the pro-survival effects of NPD1. Pull-down assays were used to assess phosphorylation of Ataxin-1 in response to the lipid mediator.
We found that the ectopic expression of Ataxin-1 containing the extended polyQ-tract induced RPE cell apoptosis, which was abrogated by the addition of DHA (100 nM)/PEDF(10 ng/mL) and the DHA oxygenation derivative, NPD1. Similarly, when Ataxin-1 containing 82 glutamines was expressed in cells deficient in 15-LOX-1 (which contains negligible amounts of NPD1), the apoptosis was severely enhanced; however, in this case only NPD1 (50 nM) rescued them from cell death. Furthermore, NPD1 reduced the misfolded-Ataxin-1-induced accumulation of pro-apoptotic Bax in the cytoplasm, suggesting that NPD1 acts by preventing pro-inflammatory signaling pathways from taking place. Finally, NPD1 signaling interfered with the Ataxin-1/capicua repression of gene expression and decreased the content of phosphorylated Ataxin-1, suggesting that the lipid mediator’s signaling modulates the formation or stabilization of the Ataxin-1 complexes.
Together the data suggest that NPD1 promotes the survival of RPE cells through the modulation of pro/anti-apoptotic and inflammatory pathways induced by the proteotoxic stress triggered by abnormally folded Ataxin-1 (NIH/NEI Grant R01EY005121).
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