Genetic supplementation of RDS alleviates a loss-of-function phenotype in C214S model of retinitis pigmentosa.

Mutations in the photoreceptor-specific protein, Rds, have been associated with a large number of inherited retinal degenerative diseases. Reports have described the incidence of retinitis pigmentosa, cone-rod dystrophy, diffuse retinal dystrophy, macular degeneration, and central areolar choroidal dystrophy in patients carrying mutations in the RDS gene (Dryja, Hahn, Kajiwara, & Berson, 1997; Ekstrom et al., 1998; Fishman et al., 1997; Fossarello et al., 1996; Jacobson, Cideciyan, Kemp, Sheffield, & Stone, 1996; Nakazawa, Wada, Chida, & Tamai, 1997; Sears, Aaberg, Daiger, & Moshfeghi, 2001; Zhang, Garibaldi, Li, Green, & Zack, 2002). As a membrane glycoprotein located in the disc rim region in the OSs of rods and cones (Connell & Molday, 1990; Molday, Hicks, & Molday, 1987; Travis, Brennan, Danielson, Kozak, & Sutcliffe, 1989), Rds is thought to be necessary for disc assembly, maintenance and renewal (Boesze-Battaglia & Goldberg, 2002; Molday et al., 1987; Wrigley, Ahmed, Nevett, & Findlay, 2000). While current beliefs propose Rds to serve a primarily structural role in OSs, alterations in Rds have strong functional as well as structural implications since this is the region where phototransduction occurs (Ridge, Abdulaev, Sousa, & Palczewski, 2003). Complete absence of the protein in the retinal degeneration slow (rds) mouse (van Nie, Ivanyi, & Demant, 1978) results in a failure of OS formation, an absence of retinal function, and the progression of photoreceptor degeneration (Cohen, 1983; Jansen & Sanyal, 1984; Sanyal, De Ruiter, & Hawkins, 1980; Sanyal & Jansen, 1981). A phenotype of haploinsufficiency has also been reported to associate with the under-expression of Rds (in rds+/− animals) and is characterized by malformed and swirl-like OSs, and an early-onset of slow rod degeneration followed by a late-onset and slow cone degeneration (Cheng et al., 1997; Nour, Ding, Stricker, Fliesler, & Naash, 2004). In addition to the rds null mutant (Ali et al., 2000; Sarra et al., 2001; Schlichtenbrede et al., 2003), two transgenic mouse models have been generated (Kedzierski, Lloyd, Birch, Bok, & Travis, 1997; Kedzierski et al., 2001), one of which, P216L, has been used to evaluate therapeutic interventions for the treatment of Rds-associated retinal disease (Bok et al., 2002; Liang et al., 2001). However, to date no study has reported both significant functional and structural rescue in any animal model carrying point mutations in the rds gene. In this study, we assessed the feasibility of Rds supplementation to resolve rod defect associated with expression of the C214S mutant of Rds. The C214S mutation causes a loss-of-function defect which primarily affects rods in humans and mice (Saga et al., 1993; Stricker, Ding, Quiambao, Fliesler, & Naash, 2005). To reduce the effect of the mutant protein by competing it out with the wild-type (WT) protein, we generated a transgenic line expressing the WT Rds in both rods and cones driven by the human interphotoreceptor retinoid binding protein (hIRBP) promoter (Nour et al., 2004). A single residue change at the C-terminus was incorporated in the WT transgene to mimic the human sequence that would facilitate specific recognition of the transgene product (Nour et al., 2004). This change is proline to glutamine at position 341 (P341Q), and here the line is named NMP for normal mouse peripherin/rds. Structural and functional studies on NMP retinas demonstrated the benign effect of the P341Q modification (Nour et al., 2004). Uniform expression of Rds in rods and cones was achieved by crossing C214S mice with NMP mice. By studying the structure of the double transgenic retinas by histology and the function by electroretinography, we have shown that genetic supplementation of WT Rds is a viable option for loss-of-function mutations in the RDS. As proof-of-principle, this finding provides a basis for the development of future therapeutic approaches. The following represents original material, not previously published or under consideration for publication elsewhere.