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Steven J Pittler, Stephanie Davis, Sriganesh Ramachandra Rao, Delores A. Stacks, Marci L DeRamus, Steven J Fliesler; Selective RPE-ablation of dehydrodolichyl diphosphate synthase (DHDDS) causes morphologic changes similar to geographic atrophy in dry AMD. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5912.
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DHDDS (RP59) is required for the synthesis of functional dolichols that are essential for N-linked glycosylation of proteins. To assess the effects of selective ablation of DHDDS in RPE we generated and analyzed Dhdds conditional knockout mice.
A Cre conditional knockout construct (KOMP, UC Davis) was bred onto a C57Bl/6J background, and these mice were crossed to VMD2-RPE-Cre mice (Yun Le, OUHSC). The resulting homozygous (hz) and heterozygous (het) RPE-Dhdds-ko, VMD2-RPE-Cre, and C57Bl/6J control lines were analyzed by fundus exam, fluorescein angiography, histology, ERG, and optokinetic reflex (OKR). OKR was performed at a constant speed of 12d/s and contrast sensitivity determined at several spatial frequencies. Student’s t-test was used to compare differences between group responses (stat. signif., p<0.05).
No pathology was observed in retinas of het RPE-Dhdds-ko or control lines examined from 1 to 3 mo. Abnormal pigmentation was observed in the fundus of 8- and 10-mo old hz RPE-Dhdds-ko mice; vascular changes, including microanuerisms, increased vessel tortuosity and attenuation, were also observed by 6 mo of age. Homozygous RPE-Dhdds-ko mice at 2 and 3 mo displayed geographic RPE atrophy, photoreceptor shortening and loss, RPE transmigration into the retina, and external limiting membrane (ELM) descent towards Bruch’s membrane. At 2 mo of age, hz and het RPE-Dhdds-ko mice exhibited reduced scotopic ERG a- (39% and 17%) and b-wave (49% and 40%) responses compared to WT (p<0.05). At 3 mo, scotopic ERG a-wave amplitudes were reduced in hz RPE-Dhdds-ko (83%), while b-wave responses were reduced in both genotypes (84% and 28%, p<0.05). Photopic ERG responses in hz RPE-Dhdds-ko mice showed reductions in a- (86%) and b-wave (95%) responses (p<0.05). OKR analysis showed reductions in photopic (4-31%) and scotopic (8-29%) contrast sensitivity over the range of 0.031 to 0.272 c/d in 3-mo old hz RPE-Dhdds-ko mice (p<0.05). No differences in spatial acuity were observed.
Potential perturbation of DHDDS-dependent processes selectively in the RPE may cause the observed structural and functional deficits in RPE and photoreceptors. The slowly progressing nature of these defects suggests there may be a window of opportunity to identify key proteins that are involved in directing the observed dry AMD-like pathology.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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