Structural recovery of the retina in a retinoschisin-deficient mouse after gene replacement therapy by solid lipid nanoparticles

X-linked juvenile retinoschisis (XLRS) is a retinal degenerative disorder caused by mutations in the RS1 gene encoding a protein termed retinoschisin. The disease is an excellent candidate for gene replacement therapy as the majority of mutations have been shown to lead to a complete deficiency of the secreted protein in the retinal structures. In this work, we have studied the ability of non-viral vectors based on solid lipid nanoparticles (SLN) to induce the expression of retinoschisin in photoreceptors (PR) after intravitreal administration to Rs1h-deficient mice. We designed two vectors prepared with SLN, protamine, and dextran (DX) or hyaluronic acid (HA), bearing a plasmid containing the human RS1 gene under the control of the murin opsin promoter (mOPS). In vitro, the nanocarriers were able to induce the expression of retinoschisin in a PR cell line. After injection into the murine vitreous, the formulation prepared with HA induced a higher transfection level in PR than the formulation prepared with DX. Moreover, the level of retinoschisin in the inner nuclear layer (INL), where bipolar cells are located, was also higher. Two weeks after vitreal administration into Rs1h-deficient mice, both formulations showed significant improvement of the retinal structure by inducing a decrease of cavities and PR loss, and an increase of retinal and outer nuclear layer (ONL) thickness. HA-SLN resulted in a significant higher increase in the thickness of both retina and ONL, which can be explained by the higher transfection level of PR. In conclusion, we have shown the structural improvement of the retina of Rs1h-deficient mice with PR specific expression of the RS1 gene driven by the specific promoter mOPS, after successful delivery via SLN-based non-viral vectors.