Genotypic and Phenotypic Characterization of the P23H Line 1 Rat Model

Abstract

Purpose: Rod-cone dystrophy, a member of the retinitis pigmentosa (RP) family of diseases is the most common inherited degenerative photoreceptor disease, for which no therapy is currently available. The P23H rat is one of the most commonly used autosomal dominant RP models. It has been created by incorporation of a mutated mouse rhodopsin (Rho) transgene in the wild-type (WT) Sprague Dawley rat. Detailed genetic characterization of this transgenic animal has never been fully documented. The current study proposes to fill this gap of knowledge on the P23H Line 1 (P23H-1) rat and provide additional phenotypic information applying non-invasive and state-of-the-art in vivo techniques that are relevant for preclinical therapeutic evaluations.

Methods: Transgene sequence was identified by Sanger sequencing. Using quantitative PCR (qPCR), transgene copy number was calculated and expression measured. Visual function of 1-, 2-, 3-, 6- and 7-months-old WT and P23H-1 rats was measured by full field electroretinography (ERG). Retinal structure was monitored using spectral domain optical coherence tomography (SD-OCT).

Results: Transgene sequencing reveals a P23H mutated mouse Rho sequence encompassing from the promoter to the 3’UTR. qPCR analyses estimated 9 copies of the transgene present in the hemizygous and 18 copies in the homozygous rats. In 1-month-old hemizygous P23H-1 rats, transgene expression was 28% less than Rho gene in WT rats. ERG showed a progressive rod-cone dysfunction peaking at 6 months-of-age. SD-OCT confirmed a progressive thinning of the photoreceptor cells layer leading to the disappearance of the outer retina by 6 months, with additional morphological changes in the inner retinal layers in hemizygous P23H-1 rats.

Conclusions: We identified the exact sequence of the transgene inserted in the P23H-1 rat, determined the copy number and evaluated the expression. Functional and structural phenotypic and non-invasive in vivo evaluation by SD-OCT and ERG confirms previously reported data.<br /> These results shed light on the genotype of the P23H-1 rat model, better document non-invasively the RP phenotype and provide the foundation for assessing benefit from therapeutic interventions such as gene correction with this model.