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MAI SHUYI, David M Wu, Krishnakumar Kizhatil, Simon W John, Constance L Cepko, Wenjun Xiong; AAV-mediated overexpression of nuclear SREBP1/2 induces buphthalmos and retinal degeneration in mice. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4497.
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© ARVO (1962-2015); The Authors (2016-present)
Sterol regulatory element-binding proteins (SREBPs) are a small family of lipogenic transcription factors, with SREBP1 and SREBP2 regulating fatty acid and cholesterol synthesis, respectively. As there is a growing appreciation of the role of lipid metabolism in eye diseases, we sought to understand the role of the SREBPs in ocular physiology. We overexpressed the N-terminus of SREBP1 or SREBP2 (nSRE1/2), which localizes to the nucleus and becomes constitutively active. We report here a novel phenotype of buphthalmos, increased intraocular pressure (IOP), and retinal degeneration.
An AAV8 vector was constructed using a CMV promoter to drive the expression of nuclear SREBP1/2 (AAV8-CMV-nSRE1/2) in the major cell types of mouse eye, including photoreceptors and retinal pigmented epithelial (RPE) cells. AAV8-CMV-nSRE1/2 or the control AAV8-CMV-GFP was injected subretinally into the right eyes of C57BL/6J or CD1 mice at postnatal day 0 (P0). IOP measurement, optomotor and ERG tests were performed on the adult mice at various ages. Mice were sacrificed after the tests, their eyes were enucleated, and the axial length of the eyeballs was measured. The retinas were cryosectioned, immunostained, imaged and analyzed for outer nuclear layer (ONL) thickness and for markers of RPE cells, cones, Muller glia (MG), microglia and retinal ganglion cells (RGCs).
The eyes injected with AAV8-CMV-nSRE1/2 showed buphthalmia, with significantly increased axial length and equatorial diameter. AAV8-CMV-nSRE1 injected eyes had a higher IOP compared to the control eyes (17.3±0.48 mmHg vs 12.4±0.91 mmHg, p<0.0001). Optomotor evaluation showed that the visual acuity of the AAV8-CMV-nSRE1/2 injected eyes decreased drastically by P30. ERG responses were significantly dampened at P30. Photoreceptor degeneration was confirmed by ONL thinning. ZO-1, cone arrestin and Tuj1 staining showed the degeneration of RPE, cones and RGCs, and activation of MG and microglia was suggested by enhanced GFAP and Iba1 staining.
The phenotypes of the SREBP1/2 over-activating eyes are reminiscent of congenital glaucoma with buphthalmos and increased IOP. Also interesting is the coincident finding of retinal degeneration. Future studies with more specific promoters will dissect the significant roles for SREBP in ocular development and potentially the pathogenesis of retinal degenerative diseases.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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