This study demonstrated that RS protein delivery into the retina of retinoschisis
Rs1h −/Y mice can reverse the abnormal electronegative ERG waveform that characterizes the retinal functional changes in dystrophic
Rs1h-KO mice and in human XLRS disease. Knocking out the
Rs1h gene resulted in structural abnormalities in the mouse retina, including irregular formation of the neuronal and plexiform layers, and the mislocalization of ganglion cells and photoreceptor cells outside of their normal positions. Structural retinal consequences also involved schisis dissection through the INL. Although retinoschisin protein is expressed during retinal development
17 and the lack of RS causes congenital retinal structural changes, this therapy study demonstrated that treatment even of adult animals was successful in reversing the b-wave functional abnormality, presumably at the level of the photoreceptor-to-bipolar synapse.
The retinal abnormalities found in our retinoschisin
Rs1h −/Y mice overlapped those described previously by Weber et al.
33 in their
Rs1h −/Y mice, which they developed by introducing a
lacZ reporter gene in-frame into exon 3 of
Rs1h along with a
NeoR expression cassette under the separate control of the mouse
Pgk phosphoglycerate kinase gene promoter. Like our retinoschisis mice, their
Rs1h-KO model showed the characteristic electronegative ERG waveform pattern and developed splitting through the INL. They also reported a generalized decrease in rod photoreceptor cell number and a considerable reduction in cone numbers. Our
Rs1h-KO mice showed irregularity of the ONL but otherwise had essentially normal ONL cellular thickening, although the inner and outer segments were shorter. The scotopic a-wave amplitude in our
Rs1h −/Y mice was approximately one-half normal, consistent with shorter inner and outer segments.
31 This murine a-wave reduction, however, is at variance with our human ERG studies of 13 XLRS-affected men, most of whom showed normal rod a-wave maximal amplitudes.
34 RS protein replacement by introduction of the AAV(2/2)-CMV-
Rs1h construct into
Rs1h −/Y mice did not repair the retinal structure in these adult animals and hence did not reverse the reduced a-wave amplitude. It is against the baseline of the a-wave that was reduced similarly before and after introducing the gene transfer construct that the b-wave improvement is judged.