Characterization of Ocular Phenotype in Mouse Models of Bardet Biedl Syndrome and Feasibility Study for Subretinal Gene Therapy

Abstract

Purpose: : To further characterize the ocular phenotype of a knock-in mouse model of Bardet Biedl syndrome (BBS) harboring an M390R mutation in Bbs1 and a knock-out model of Bbs3, and to determine the feasibility of subretinal gene therapy.

Methods: : M390R Bbs1 knock-in mice and Bbs3 knock-out mice were generated using homologous recombination and ES cell technologies. Homozygous mutant mice were generated for each gene (Bbs1M390R/M390R; Bbs3-/-). Pupillometry, electroretinography, fundus examination and photography and histology were performed in young and old mice. A gene replacement therapy protocol using subretinal injection of AAV viral vector with wild type Bbs1 was developed.

Results: : Bbs1M390R/M390R mice demonstrated abnormal pupillary responses at 2-3 months of age. Electroretinogram amplitudes were diminished starting at age 3-4 months progressing to almost non-recordable at 6 months. Bbs3-/- mice demonstrated almost non-recordable electroretinograms by 7 months of age. A distinct lobular pigmentary pattern was observed in Bbs3 deficient mice on fundus exam, as was marked optic atrophy, likely due to hydrocephalus in these animals. Subretinal injection of reporter genes and AAV-WT Bbs1 gene constructs was performed in Bbs1M390R/M390R and wild type mice. Short term electrophysiology and fundus examination demonstrated no adverse effects to the retina compared to the uninjected eye. An injected eye demonstrated rod photoreceptor cell labeling with an antibody directed against BBS1.

Conclusions: : Mice lacking the Bbs3 gene recapitulate the retinal degeneration seen in humans, as well as having hydrocephalus and optic atrophy. M390R Bbs1 mice recapitulate the human retinal degeneration. Subretinal injection of AAV with reporter molecules and with the wild type Bbs1 gene has been performed without adverse affect on the retina.

Keywords: genetics • mutations • retinal degenerations: hereditary