Selective ablation of dehydrodolichyl diphosphate synthase (Dhdds) expression in RPE causes morphologic changes similar to dry AMD

Title Selective ablation of dehydrodolichyl diphosphate synthase (Dhdds) expression in RPE causes morphologic changes similar to dry AMD
Author, Co-Author Steven Pittler, Stephanie Davis, Marci DeRamus, Bruce Pfeffer, Sriganesh Rao, Delores Davis, Steven Fliesler
Topic Treatment and Management of Posterior Sgmt Disease
Year
2016
Day
Thursday
Program Number
165150
Room
Ballroom A-B
Affiliation
University of Alabama at Birmingham
Abstract Purpose: Mutations in the human gene encoding dehydrodolichyl diphosphate synthase (DHDDS), which is required for N-linked protein glycosylation, cause retinitis pigmentosa (RP). We generated a conditional Dhdds knockout (KO) mouse model to study the effects of cell type-specific ocular Dhdds deficiency.

Methods: Dhdds construct was introduced into murine ES cells and confirmed by PCR. Established mouse lines were bred to homozygosity and these mice were crossed to RPE-Cre mice (Yun Le, OUHSC). The resulting RPE-Dhdds-/- and control mice were assessed by OCT, ERG, histology, immunofluorescence, and TEM at 1, 2, and 3 mo postnatal.

Results: Cre-dependent GFP reporter expression indicated that >90% of RPE cells expressed Cre by 3 mo of age. OCT analysis of RPE-Dhdds-/- mice showed a significant reduction (vs. WT) in retinal thickness at all ages analyzed. No OCT changes were observed in RPE-Dhdds+/- mice. In RPE-Dhdds-/- mice, histologic analysis showed panretinal degeneration affecting the RPE and photoreceptor layers, that was similar to geographic atrophy seen in dry AMD. Additionally, TEM of 3 mo old homozygous mice revealed ectopic RPE migration into the retinal space, and displacement of the ELM. In 1 mo old RPE-Dhdds+/- mice, no differences from WT were observed in the scotopic ERG. However, RPE-Dhdds-/- mice exhibited significant reduction (42%, p < 0.01) in b-wave amplitudes compared to WT, with normal a-wave amplitudes. By 2 mo of age, hets (RPE-Dhdds+/-) showed a significant reduction in both the a-wave (17%, p < 0.05) and b-wave (44%, p < 0.001). These deficits were more pronounced in RPE-Dhdds-/- mice (a-wave, 42%, p < 0.01; b-wave, 52%, p < 0.001).

Conclusion: Homozygous Dhdds conditional KO mice exhibit progressive RPE and retinal degeneration with structural deficits similar to several features observed in dry AMD, suggesting a possible nexus of disease pathobiology between congenital disorders of N-glycosylation and AMD.
Affiliation of Co-Authors University of Alabama at Birmingham, University of Alabama at Birmingham, SUNY-Buffalo/VA Med Ctr-Buffalo, SUNY-Buffalo/VA Med Ctr-Buffalo, University of Alabama at Birmingham, SUNY-Buffalo/VA Med Ctr-Buffalo
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