Author ORCID Identifier

https://orcid.org/0000-0001-5260-6635

Semester

Fall

Date of Graduation

2024

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Not Listed

Committee Chair

Saravanan Kolandaivelu

Committee Member

Maxim Sokolov

Committee Member

Visvanathan Ramamurthy

Committee Member

Bradley Webb

Committee Member

Peter Mathers

Abstract

Progressive Rod-Cone Degeneration (PRCD) is a peripheral membrane protein predominantly expressed in photoreceptor outer segment (OS) disc membranes with an unknown function. Several mutations in Prcd are implicated in Retinitis pigmentosa (RP) in humans. The most common “cysteine to tyrosine” (C2Y) mutation in Prcd leads to progressive retinal atrophy in multiple dog breeds and RP in humans. Canine models harboring the C2Y mutation in Prcd show disorganized OS structure with greatly attenuated photoreceptor OS renewal rates. Recent studies show defects in the photoreceptor nascent disc flattening in the absence of Prcd. However, it is unclear how OS discs eventually flatten and why only some but not all the photoreceptors are affected. Decreased levels of Docosahexaenoic acid (DHA, 22:6n-3) in the OS, and both DHA and cholesterol in the plasma are previously reported in Prcd-mutant canines but the potential alterations in the levels of retinal cholesterol in the absence of Prcd remain unexplored. In this dissertation research, we first used a global Prcd knockout mouse model to investigate both the alterations in the retinal cholesterol levels and the under-studied pathophysiological changes that occur in the retinal pigment epithelium (RPE) in the absence of PRCD. We report multiple lines of evidence supporting elevated levels of cholesteryl esters (CEs) in the photoreceptors, and the accumulation of lipid deposits in the RPE of Prcd-/- mice when compared to wildtype controls. Prcd-deficient mice exhibit thickened Bruch’s membrane (BrM), subretinal and sub-RPE drusenoid focal deposits that together mimic an age-related macular degeneration (AMD)-like phenotype and further corroborate cholesterol dysregulation. We additionally report extensive lipofuscin accumulation and propose that it can lead to RPE lysosomal dysfunction which may underlie the impaired phagocytosis observed in Prcd-deficient mice. Secondly, we generated and characterized the first ever PrcdC2Y/C2Y murine model. We show that the phenotypic manifestations of the disease, albeit identical to Prcd-/- mice, are delayed in the PrcdC2Y/C2Y mice suggesting that C2Y could be a hypomorphic mutation. Altogether, our data strongly support altered retinal cholesterol levels in the absence of PRCD and identify dysregulated cholesterol homeostasis as the crux of the structural and functional deficits observed in the PRCD-deficient retina. In addition, the work presented in this dissertation is the most comprehensive study of the RPE in Prcd-deficient models, providing novel insights into the structural and functional integrity of the RPE in the absence of PRCD.

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