The AMD-like Disease in Ccl2-/- and Cx3cr1-/- Mice is Dependent on the Crb1rd8 Retinal Degeneration Mutation Not the Loss of the Chemokine/Chemokine Receptors

Abstract

Purpose: : To report that the disease phenotype Ccl2^-/- and Cx3cr1^-/- chemokine deficient mice is independent of the loss of Ccl2^-/- or Cx3cr1^-/- but the result of the Crb1^rd8 retinal degeneration mutation found in these mouse lines.

Methods: : Ccl2^-/-/Cx3cr1^-/- mice were used to generate Ccl2^-/-, Cx3cr1^-/-, and heterozygous littermate control mouse lines. Ccl2^-/-/Cx3cr1^-/- mice were also backcrossed 8 generations with C57BL/6 mice to generate Ccl2^-/-/Cx3cr1^-/- mice on the pure C57/BL6 background. Resultant mice were examined for pathology and signs of ocular disease as reported for these chemokine /chemokine receptor deficient mice. All resultant strains, including the original parental strains Ccl2^-/- and Cx3cr1^-/- used to produce the Ccl2^-/-/Cx3cr1^-/- mice, were genotyped for the Crb1^rd8 retinal degeneration mutation by PCR and results were compared to observed pathology.

Results: : Retinal disease in all mouse lines was 100% associated with the genotype Crb1^rd8/Crb1^rd8 and was unrelated to the deletion of Ccl2^-/- and/or Cx3cr1^-/-. All mice heterozygous for Crb1^rd8, as well as those that were wildtype at the Crb1 locus, showed no signs of disease; this included the Ccl2^-/-/Cx3cr1^-/-, Ccl2^-/- and Cx3cr1^-/- mouse lines. All Ccl2^-/-/Cx3cr1^-/-, Ccl2^-/- and Cx3cr1^-/- mice on the C57/BL6 background were wildtype at the Crb1 locus and showed no signs of ocular disease.

Conclusions: : The disease phenotype observed in the Ccl2^-/-/Cx3cr1^-/- mouse strain as well as the single knockout parental strains is independent of the loss of the chemokine and/or chemokine receptor but correlates with the presence of the Crb1^rd8 retinal degeneration mutation. These results demonstrate that background genes must be carefully examined when developing mouse models to mimic human ocular disease. The results also suggest that the loss of Ccl2 and/or Cx3cr1 may not predispose mice to an AMD-like phenotype.

Keywords: age-related macular degeneration • retinal degenerations: hereditary • retinal pigment epithelium