Presence of rd8 mutation does not effect the Lete-Onset Retinal Degeneration (L-ORD) phenotype in C57BL/6 mice with S163R Ctrp5/C1qtnf5 mutation

Abstract

Purpose: To study the influence of Crb1 c.3481delC (rd8) mutation on the retinal phentoype of the L-ORD mouse model with heterozygous S163R missense mutation in the C1Q-Tumor Necrosis Factor Related Protein-5 (C1QTNF5/CTRP5) gene.

Methods: Mouse model for L-ORD was generated on C57BL/6J background and the presence of rd8 mutation was observed in this colony. To study the influence of the rd8 mutation on L-ORD phenotype, mouse lines carrying both the Ctrp5 S163R and the rd8 mutation (Ctrp5^+/-;rd8/rd8), without the rd8 mutation (Ctrp5^+/-;wt/wt); and wild type mice with and without the rd8 mutation (Wt^rd8/rd8 and Wt^wt/wt, respectively) were generated. Genotyping was carried out by allelic polymerase chain reaction (PCR) or sequencing. Retinal morphology was studied by fundus imaging, histology, light microscopy, electron microscopy and immunohistochemistry.

Results: Genotype analysis of the mice in L-ORD mouse colony detected the rd8 mutation in both the homozygous or heterozygous states. Fundus imaging revealed an accelerated accumulation of AF spots with age in Ctrp5^+/-;wt/wt. The number of AF spots was significantly increased with age in Ctrp5^+/;wt/wt mice when compared to age matched controls. The presence of pseudorosette structures, the hallmark pathology in rd8 mice, was not observed in any genotypes studied. Further, the external limiting membrane was continuous in Ctrp5^+/-;rd8/rd8 and Wt^rd8/rd8 mice. The Ctrp5^+/-;wt/wt mice developed characteristic L-ORD pathology including age-dependent accumulation of AF spots, development of prominent sub-RPE and basal laminar deposits and Bruch’s membrane abnormalities at an older age, while these changes were not observed in age-matched littermate Wt^wt/wt mice.

Conclusions: The Wt^rd8/rd8 and Ctrp5^+/-;rd8/rd8 mice raised on C57BL/6J did not develop early onset retinal changes that are characteristic of the rd8 phenotype supporting the hypothesis that manifestation of rd8-associated pathology is dependent on the genetic background. The lack of rd8- associated retinal pathology in the Ctrp5^+/-;wt/wt mouse model raised on the C57BL/6J background and the development of the L-ORD phenotype in these mice in the presence and absence of rd8 mutation suggests that the pathology observed in Ctrp5^+/-;wt/wt mice is primarily associated with the S163R mutation in the Ctrp5 gene.