Loss of PRCD alters number and packaging density of rhodopsin in rod photoreceptor disc membranes

Emily R Sechrest,Saravanan Kolandaivelu,Subhadip Senapati,Joseph Murphy,Paul S.-H Park,Andrew F X Goldberg

doi:10.1038/s41598-020-74628-2

Abstract

Progressive rod-cone degeneration (PRCD) is a small protein localized to photoreceptor outer segment (OS) disc membranes. Several mutations in PRCD are linked to retinitis pigmentosa (RP) in canines and humans, and while recent studies have established that PRCD is required for high fidelity disc morphogenesis, its precise role in this process remains a mystery. To better understand the part which PRCD plays in disease progression as well as its contribution to photoreceptor OS disc morphogenesis, we generated a Prcd-KO animal model using CRISPR/Cas9. Loss of PRCD from the retina results in reduced visual function accompanied by slow rod photoreceptor degeneration. We observed a significant decrease in rhodopsin levels in Prcd-KO retina prior to photoreceptor degeneration. Furthermore, ultrastructural analysis demonstrates that rod photoreceptors lacking PRCD display disoriented and dysmorphic OS disc membranes. Strikingly, atomic force microscopy reveals that many disc membranes in Prcd-KO rod photoreceptor neurons are irregular, containing fewer rhodopsin molecules and decreased rhodopsin packing density compared to wild-type discs. This study strongly suggests an important role for PRCD in regulation of rhodopsin incorporation and packaging density into disc membranes, a process which, when dysregulated, likely gives rise to the visual defects observed in patients with PRCD-associated RP.

Highlights

Progressive rod-cone degeneration (PRCD) is a small protein localized to photoreceptor outer segment (OS) disc membranes
Along with evidence of retinal degeneration in these models and structural defects exacerbated by microglia recruitment to clear these vesicles, it is clear that PRCD is required for proper OS maintenance and disc morphogenesis; further studies are needed to clarify the precise mechanistic role which PRCD plays in these processes
To investigate the interplay between rhodopsin and the observed defects in the Prcd-KO rod OS (ROS) ultrastructure, we evaluated ROS disc membranes isolated from Prcd-KO mice and age matched WT controls by atomic force microscopy (AFM)

Summary

Introduction

Progressive rod-cone degeneration (PRCD) is a small protein localized to photoreceptor outer segment (OS) disc membranes. PRCD’s specific role within the photoreceptor remains elusive, recent studies in a PRCD knockout mouse model have identified a requirement for PRCD in high fidelity disc morphogenesis. In this model, it is observed that discs do not flatten or form properly in the absence of PRCD. Along with evidence of retinal degeneration in these models and structural defects exacerbated by microglia recruitment to clear these vesicles, it is clear that PRCD is required for proper OS maintenance and disc morphogenesis; further studies are needed to clarify the precise mechanistic role which PRCD plays in these processes

Methods

Results

Conclusion