Lentivirus-mediated expression of cDNA and shRNA slows degeneration in retinitis pigmentosa

Mutations in Pde6b lead to high levels of signaling molecules cyclic guanosine monophosphate (cGMP) and Ca2+, which ultimately result in photoreceptor cell death in certain forms of retinitis pigmentosa (RP). The level of cGMP, which is controlled by opposing activities of guanylate cyclase (GUCY) and photoreceptor phosphodiesterase-6 (PDE6), regulates the opening of cyclic nucleotide-gated ion channels [CNG] and thereby controls Ca2+ influx into the outer segments. Using a lentiviral gene therapy approach, we have previously shown that degeneration can be temporarily slowed either by introducing wild-type PDE6 beta or knocking down expression of GUCY2E and CNGA1 in photoreceptors of Pde6b(H620Q), a mouse model for RP. Rescue was transient with either approach. Therefore, we tested a novel combination therapy using bipartite lentiviral vectors designed to both introduce wild-type PDE68 expression and knockdown GUCY2E or CNGA1. Immunoblot analysis shows simultaneous increases in PDE6 beta and decreases in GUCY2E or CNGA1 in retinas transduced by the vectors, indicating successful transduction. In Pde6b(H620Q) mutants, we observe rescue of photoreceptor function and an increase in photoreceptor rows as compared with untreated controls. However, no evidence of prolonged rescue beyond the limit of the previously tested single therapy was observed.