Bilberry extract administration prevents retinal ganglion cell death in mice via the regulation of chaperone molecules under conditions of endoplasmic reticulum stress

Orie Nakamura,1 Satoru Moritoh,1,2 Kota Sato,1,3 Shigeto Maekawa,1 Namie Murayama,1 Noriko Himori,1 Kazuko Omodaka,1,3 Tetsuya Sogon,4 Toru Nakazawa1–3,5 1Department of Ophthalmology, Tohoku University Graduate School of Medicine, Miyagi, Japan; 2Department of Retinal Disease Control, Tohoku University Graduate School of Medicine, Miyagi, Japan; 3Department of Ophthalmic Imaging and Information Analytics, Tohoku University Graduate School of Medicine, Miyagi, Japan; 4R&D Department, Wakasa Seikatsu Co., Ltd., Kyoto, Japan; 5Department of Advanced Ophthalmic Medicine, Tohoku University Graduate School of Medicine, Miyagi, Japan Purpose: To investigate the effect of bilberry extract anthocyanins on retinal ganglion cell (RGC) survival after optic nerve crush. Additionally, to determine details of the mechanism of the neuroprotective effect of bilberry extract anthocyanins and the involvement of endoplasmic reticulum stress suppression in the mouse retina.Materials and methods: Anthocyanins in bilberry extract (100 mg/kg/day or 500 mg/kg/day) were administrated orally to C57BL/6J mice. The expression levels of various molecular chaperones were assessed with quantitative reverse-transcription polymerase chain reaction, Western blotting, and immunohistochemistry. RGC survival was evaluated by measuring the gene expression of RGC markers and counting retrogradely labeled RGCs after optic nerve crush.Results: The protein levels of Grp78 and Grp94 increased significantly in mice after bilberry extract administration. Increased Grp78 and Grp94 levels were detected in the inner nuclear layer and ganglion cell layer of the retina, surrounding the RGCs. Gene expression of Chop, Bax, and Atf4 increased in mice after optic nerve crush and decreased significantly after oral bilberry extract administration. RGC survival after nerve crush also increased with bilberry extract administration.Conclusion: These results indicate that oral bilberry extract administration suppresses RGC death. Bilberry extract administration increased Grp78 and Grp94 protein levels, an effect which may underlie the neuroprotective effect of bilberry extract after optic nerve crush. Thus, bilberry extract has a potential role in neuroprotective treatments for retinal injuries, such as those which occur in glaucoma. Keywords: bilberry extract, molecular chaperones, ER stress, retinal ganglion cells, glaucom