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Sarah Xin Zhang, Evgenii Boriushkin, Gail M Seigel, Joshua Jianxin Wang; Identification of p58IPK as a Novel Protective Factor for Retinal Neuronal Survival. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5742.
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© ARVO (1962-2015); The Authors (2016-present)
Neuronal degeneration is a common feature of sight-threatening retinal diseases including diabetic retinopathy and glaucoma and involves multiple etiological factors such as ER stress. p58IPK is an ER-resident chaperone protein, playing a vital role in regulation of protein folding and biosynthesis. The goal of our study is to examine the role of p58IPK in retinal neuronal cells under normal and stressed conditions.
Expression and cellular localization of p58IPK, retinal morphology and retinal function were characterized in p58IPK knockout (KO) and/or wildtype (WT) mice. ER stress, apoptotic cell death, and apoptotic gene expression were examined in p58IPK KO and WT mice challenged with intravitreal injection of N-Methyl-D-aspartic acid (NMDA, 20nmol/eye). In in vitro experiments, differentiated R28 retinal neuronal cells were transduced with adenovirus encoding p58IPK (Ad-p58IPK) or control virus (Ad-LacZ) and then exposed to tunicamycin (TM) or hydrogen peroxide (H2O2). Levels of ER stress, apoptosis, and cell survival were evaluated with western blotting, immunostaining, TUNEL and MTT cell viability assay.
p58IPK is expressed mainly in retinal ganglion cells (RGC), neurons in the inner nuclear layer (INL) and the inner segment of photoreceptor cells. Young p58IPK KO mice have normal retinal structure and function but exhibit increased CHOP expression and loss of RGCs with aging (8-10 months). Intravitreal injection of NMDA induced retinal ER stress and enhanced expression of p58IPK. In p58IPK KO mice, injection of NMDA resulted in greater ER stress, further reduced bcl-2 expression and worsened apoptosis of RGCs and neurons in retinal INL. In cultured R28 cells, both TM (0.1 - 0.5 μg/ml) and H2O2 (100 - 500 μM) increased ER stress, CHOP expression, and caspase-3 activation in a dose-dependent manner. Overexpression of p58IPK significantly reduced eIF2α phosphorylation and CHOP expression, alleviated caspase-3 and PARP activation, and protected against oxidative and ER stress-induced apoptotic cell death. Furthermore, p58IPK downregulated pro-apoptotic gene Bax and upregulated anti-apoptotic gene Bcl-2 expression in stressed neuronal cells.
p58IPK is highly expressed in RGCs and inner retinal neurons and may provide a protective role in neuronal survival and function by maintaining ER and protein homeostasis, particularly in the case of cellular stresses.
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