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Yongsoo Park, Seung Hee Lee, IN-BEOM KIM; Expression of the Endoplasmic Reticulum Chaperone GRP78 in a Retinal Degeneration Model Induced by Blue LED Exposure. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5989. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Glucose-regulated protein (GRP78) is an endoplasmic reticulum (ER) stress marker belonging to heat shock protein family. GRP78 was studied to understand relationship between ER stress and retinal degeneration (RD). However, its exact localization during RD was not revealed at cellular and subcellular levels. In this study, we elucidated cellular and subcellular location of the GRP78 in the retinal cells in blue LED-induced RD model.
Mice (7 weeks, balb/c) were exposed to 1800 lx of the blue LED for 2 h after 18 h dark adaptation. Retina was acquired at 24 and 72 h after injury. Immunohistochemistry with anti-GRP78, anti-glutamine synthetase (GS), a Müller glia marker, and anti-IBA1, a microglial marker was performed. For subcellular localization of GRP78, immunoelectron microscopy (immuno-EM) with peroxidase- or gold-conjugated Alexa 488 antibody as a secondary antibody was conducted.
In control retina, GRP78 was prominently labeled in the rod and cone layer, the inner nuclear layer (INL), and the ganglion cell layer (GCL). GRP78 expression was decreased in the rod and cone layer 24 h after light exposure, and it was increased in the inner plexiform layer (IPL) and the outer nuclear layer (ONL) after 72 h. Increased GRP78 was co-localized with GS in the RD retina, which showed Müller cell processes. Some of Müller cells ectopically positioned in the ONL in RD retina while most of them are placed in the INL. Microglial cells increased in RD retina in the ONL, and they were more strongly labeled by GRP78 than microglia in non-RD region. In control, immuno-EM revealed GRP78 localization in ER showing continuous structure from nucleus membrane of the retinal cells and also in the ER within the neural processes in the IPL and inner segments of the photoreceptor. In RD retina, GRP78 was prominently distributed in the cytoplasm of the activated microglia and process of the Müller cells, while it was not in the control retina.
In RD 72 h after blue-LED exposure, expression of the GRP78 was increased mainly in the IPL and the ONL. It was expressed in Müller cells and microglia. At subcellular level, GRP78 was exclusively located in ER of the each retinal cell. However, activated Müller cells and microglia in RD retina showed cytoplasmic localization. These findings suggest that ER stress might be closely related to glial responses in RD.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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