Aberrant Lipid Accumulation leads to Retinal Pigmental Epithelium Dysfunction and Photoreceptor Degeneration in Prcd -deficient mice

P rogressive R od- C one D egeneration (PRCD) is an integral membrane protein exclusively expressed in photoreceptor outer segment (OS) disc membranes with an unknown function. Several mutations in Prcd are implicated in Retinitis pigmentosa (RP) in humans and multiple dog breeds. Canine Prcd -mutant models show decreased levels of Docosahexaenoic acid (DHA, 22:6n-3) in the OS, and both DHA and cholesterol in the plasma. However, potential changes in the levels of retinal cholesterol remain unexplored. In the present study, we investigate both the alterations in the retinal cholesterol levels and the under-studied pathophysiological changes that occur in the RPE of Prcd -deficient mice using a global Prcd -knockout mouse model. We report multiple lines of evidence supporting elevated levels of cholesteryl esters (C.Es) in the photoreceptors, and accumulation of lipid deposits in the RPE of Prcd -deficient mice. Strikingly, Prcd -deficient mice exhibit thickened Bruch’s membrane (BrM), subretinal and sub-RPE drusenoid focal deposits mimicking an Age-related Macular Degeneration (AMD)-like phenotype. 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. Altogether, our data demonstrates structural and functional deficits in the RPE in addition to the altered total retinal cholesterol in Prcd -deficient mice.