Germline knockout of Interphotoreceptor Retinoid Binding Protein on the DBA/2J background causes loss of retinal function, axial elongation, and morphological defects

Abstract

Purpose : Interphotoreceptor retinoid binding protein (IRBP) has been shown to be an essential protein in normal eye development on the C57Bl/6J and 129/sv background. Without IRBP, mice develop severe myopia and retinal degeneration. IRBP should also be necessary in the DBA/2J background, which develops glaucoma as the mice age. The current hypothesis is that IRBP knockouts on the DBA/2J background would develop the same myopic axial elongation and severe loss of retina function and morphology as the other backgrounds.

Methods : The IRBP-ko was bred onto the DBA/2J background for 10 generations. Then DBA/2J IRBP-ko were bred as heterozygotes giving the experimental DBA/2J IRBP^ko/ko mice as well as littermate controls DBA/2J IRBP^+/+. Mice were aged to P30, before any glaucoma development and assessed for retinal function through scotopic, photopic, and flicker electroretinogram (ERG). SD-OCT and fundus imaging was conducted to observe in vivo retina morphology. External eye measurements using a noncontact micrometer were conducted postmortem to determine eye size. Additional retinal morphology was assessed through H&E staining of retinal sections.

Results : At P30, DBA/2J IRBP^ko/ko mice had a significantly longer axial length compared to wildtype DBA/2J mice (p<0.01) or C57Bl/6J IRBP^ko/ko (p<0.01). The DBA/2J IRBP^ko/ko experienced a significant loss in amplitude compared to wild-type DBA/2J for a-wave (62%), b-wave (42%), and c-wave (46%). Photopic ERG significantly decreased (68%) as did the flicker ERG (89%) compared to wildtype DBA/2J. SD-OCT imaging showed reductions in DBA/2J IRBP^ko/ko in both retina (35%) and photoreceptor (29%) thickness. Fundus images had no obvious pathology in either genotype. The ONL nuclei counts showed a loss of 38% in DBA/2J IRBP^ko/ko.

Conclusions : Loss of IRBP in the DBA/2J background results in a severe axial elongation. The DBA/2J IRBP^ko/ko mice also experience a loss of retina thickness and severe functional deficit. The magnitude of functional losses in DBA/2J IRBP^ko/ko were similar to previously-reported losses in C57Bl/6J IRBP^ko/ko mice; but the axial elongation was more severe in the DBA/2J IRBP^ko/ko strain compared to the C57Bl/6J IRBP^ko/ko strain. This excess axial elongation could be due to possible myopia related genetic loci in the DBA/2J background.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.