Effect of retinol dehydrogenase gene transfer in a novel rat model of Stargardt disease

Dysfunction of the ATPase-binding Cassette Transporter protein (ABCA4) can lead to early onset macular degeneration, in particular to Stargardt disease. To enable translational research into this form of blindness, we evaluated the effect of Cas9-induced disruptions of the ABCA4 gene to potentially generate new transgenic rat models of the disease. We show that deletion of the short exon preceding the second nucleotide-binding domain is sufficient to drastically knock down protein levels and results in accumulation of retinoid dimers similar to that associated with Stargardt disease. Overexpression of the retinol dehydrogenase enzymes RDH8 and RDH12 can to a limited extent offset the increase in the bisretinoid levels in the Abca4(Ex42-/)- KO rats possibly by restricting the time window in which retinal can dimerize before being reduced to retinol. However, in vivo imaging shows that overexpression of RDH8 can induce retinal degeneration. This may be due to the depletion in the outer segment of the cofactor NADPH, needed for RDH function. The translational potential of RDH therapy as well as other Stargardt disease therapies can be tested using the Abca4 knockdown rat model.