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J. C. de Rivero Vaccari, P. K. Mukherjee, N. G. Bazan; Neuroprotectin D1 Reduces Cell Death Caused By Polyglutamine Ataxin-1 Expansions. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2076.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the effects of neuroprotectin D1 (NPD1), a docosahexaenoic acid (DHA) derivative, during expression of the polyglutamine ataxin-1 (82Q) protein, which causes spinocerebellar ataxia type 1 (SCA1). In this disease, retinal degenerative changes have also been described.
ARPE-19 and primary human RPE cells were cultured and transfected with either normal (30Q) or abnormal polyglutamine (82Q) ataxin-1 constructs. NPD1 or DHA (+/-pigment-epithelium derived factor (PEDF), which stimulates the synthesis of NPD1) were added to the cultures, and cell survival was analyzed by Hoechst staining at several time points. Cells were also transfected with human COX-2 luciferase construct alone or in conjunction with 82Q, and luciferase assays were performed. Immunocytochemistry was carried out to detect levels of ataxin-1, Bax, and Bcl-2.
82Q increases cell death which is attenuated by either NPD1 or DHA (+/- PEDF). NPD1 protects from 82Q-mediated cell death in a concentration dependent fashion, and 50 nM NPD1 provides the greatest protection. Transfection with the AxH domain of the ataxin-1 protein also increases apoptosis, which is prevented by NPD1. Luciferase studies indicate that COX-2 expression increases in the presence of 82Q, while NPD1 and DHA+PEDF decrease it. In addition, our results show that in the presence of 82Q, NPD1 and DHA+PEDF enhance cell survival by decreasing Bax immunoreactivity, while increasing Bcl-2 signal.
SCA1 is an autosomal dominant inherited disease in which polyglutamine expansions in the protein ataxin-1 contribute to cerebellar and brainstem neurodegeneration with the subsequent progression of ataxia. Studies indicate that polyglutamine repeats lead to protein misfolding and formation of nuclear aggregates. As the polyglutamine expansions increase, neurotoxicity and formation of nuclear aggregates increase as well. Our laboratory has previously demonstrated that NPD1 promotes ARPE-19 cell survival from oxidative stress through the activation of a mechanism that upregulates anti-apoptotic proteins, while downregulating pro-apoptotic proteins. This study demonstrates that NPD1 and DHA+PEDF decrease COX-2 gene expression and cell death caused by polyglutamine ataxin-1 expansions. NPD1 also increases Bcl-2 immunoreactivity while downregulating Bax signals, thus promoting cell survival. Our results suggest a neuroprotective role for NPD1 in polyglutamine expansion disease.
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