Retinal Disease Phenotype of the RDSF Briard-Derived RPE65-/- Dog

Abstract

Abstract: : Purpose. A naturally occurring canine RPE65-/- mutation, the cause of canine Lebers congenital amaurosis in the briard dog, provides a large animal model for the human disease. A laboratory strain of dogs has been derived from an affected male briard bred to colony dogs at the Retinal Disease Study Facility (RDSF), and used for asssesment of potential therapies. To establish baseline data, we have characterized the morphologic disease of the RDSF-derived strain of dogs. Methods. Age matched RPE65-/- and wt dogs were enucleated at different ages and their eyes were either fixed in paraformaldehyde, embedded in OCT, and then frozen-sectioned for immunocytochemical examination, or fixed in glutaraldehyde/formaldehyde, epon embedded and sectioned for morphological evaluation. Results. Examination of epon sections showed that by 16 weeks the rod outer segments (ROS) are slightly irregular in the RPE65-/- mutant. By 11 months the inferior retina showed very early retinal degeneration, characterized by shortening of ROS, but there was no apparent loss of outer nuclear layer nuclei. In contrast, disease in the superior retina was limited to ROS irregularities similar to that observed at 4 months. No morphological abnormalities were apparent in OCT embedded frozen sections except for lipid inclusions. These were present in the RPE of all diseased animals and were larger and more numerous in older animals. RPE65 protein was absent in the mutant dogs; all other retinal antigens examined (e.g. cone opsin, rhodopsin and insoluble IPM cone sheath) were expressed similarly between the mutant and wild type eyes. Conclusions. The RPE65-/- mutant shows abnormalities limited to the ROS at a young age; these progress slowly to a mild degeneration that is first observed in the inferior retina in the older animal. The preservation of photoreceptors during the first year of life gives a broad time window to examine the efficacy of therapies in this class of retinal diseases.

Keywords: retinal degenerations: hereditary • retinal pigment epithelium • microscopy: light/fluorescence/immunohistochem