Functional Compensation in a Mouse Model of Inherited Retinal Degeneration Caused by a C-terminal Prph2 Truncation Mutation.

Abstract

Purpose : A broad variety of progressive retinal diseases are caused by mutations in PRPH2. This gene encodes peripherin-2/rds (P/rds), an integral membrane protein that shapes rod and cone photoreceptor outer segment (OS) disks. Instances of human pattern dystrophy have been associated with a TYR285stop nonsense mutation predicted to truncate the protein’s cytoplasmic C-terminus. To advance understanding of inherited retinal degenerations caused by defects in PRPH2, we have generated and are investigating a TYR285stop gene-edited mouse model.

Methods : TYR285stop mice (Prph2^Y285x/Y285x and Prph2^Y285x/+) generated via CRISPR/Cas9 gene editing were outcrossed onto the C57BL6/J background until congenic. Prph2^Y285x/Y285x and Prph2^Y285x/+ mutants were compared at postnatal day 21 to WT and to Prph2^rds/rds and Prph2^rds/+ age-matched controls. Phenotyping assays included: western blotting, retinal layer thickness evaluations in paraffin sections, retinal whole mount IHC 3D imaging, full-field electroretinography (ERG), and rod spherule synaptic ribbon counts.

Results : Prph2^Y285x/Y285x mice developed significantly reduced (25%) numbers of photoreceptors which were unable to elaborate OSs. In contrast, the Prph2^Y285x/+ disease model mice developed normal numbers of photoreceptors, which elaborated OSs with abnormal ultrastructure, but a near-normal IS-OS layer thickness. Compared to WT, Prph2^Y285x/+ retinas expressed less P/rds (49%), rhodopsin (45%), rom1 (49%), and GARPs (66%). Scotopic ERG showed that although rod photoreceptor a-waves were significantly reduced (50%), rod-mediated b-wave amplitudes were maintained at WT levels. Photopic ERG showed that cone-mediated responses (b-wave amplitudes) were also near-normal. No changes were detected in the number of synaptic ribbons present in rod terminals.

Conclusions : The P/rds C-terminus was found to be essential for in vivo protein stability and function for OS morphogenesis and structure. The most striking phenotype observed for the new Prph2^Y285x/+ disease model was a robust functional compensation, which restored rod-derived signaling, likely lost as a result of OS structural damage. The new findings may reflect an example of homeostatic plasticity at the photoreceptor-bipolar cell synapse, and introduces the possibility this mechanism also applies to instances of human pattern dystrophy associated with the TYR285stop defect.

This is a 2021 ARVO Annual Meeting abstract.