Prph2 mutant knock-in mice recapitulate all features of human central areolar choroidal dystrophy and reveals an aberrant synaptic remodelling and microglial activation

Abstract Purpose Central areolar choroidal dystrophy is an inherited disorder characterized by progressive choriocapillaris atrophy and retinal degeneration, usually associated with mutations in the PRPH2 gene. We aimed to generate and characterize a mouse model with the p.Arg195Leu mutation previously described in patients.Methods Heterozygous (Prph2WT/KI) and homozygous (Prph2KI/KI) mice have been generated using the CRISPR/Cas9 system to introduce the Arg195Leu mutation. Retinal function was assessed by electroretinography and optomotor test at 1, 3, 6, 9, 12, and 20 months of age. The structural integrity of the retinas was evaluated at the same ages using optical coherence tomography. Immunofluorescence and transmission electron microscope images of the retina were also analyzed.Results Genetic sequencing confirmed that both Prph2WT/KI and Prph2KI/KI mice presented the p.Arg195Leu mutation. A progressive loss of retinal function was found in both mutant groups, with significantly reduced visual acuity from 3 months of age in Prph2KI/KI and from 6 months of age in Prph2WT/KI mice. Decreased amplitudes in the electroretinography responses were observed from 1 month of age in Prph2KI/KI and from 6 months of age in Prph2WT/KI. Morphological analysis of the retinas correlated with functional findings, showing a progressive decrease in retinal thickness of mutant mice, with earlier and more severe changes in the homozygous mutant mice. We corroborated the alteration of the outer segment structure, and we found changes in the synaptic connectivity in the outer plexiform layer as well as gliosis and signs of microglial activation.Conclusions The new Prph2WT/KI and Prph2KI/KI murine models show a pattern of retinal degeneration similar to that described in human patients with CACD and appear as good models to study the mechanisms involved in the onset and the progression of the disease, as well as to test the efficacy of new therapeutic strategies.