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UBC Theses and Dissertations

Novel therapeutic approaches for the treatment of childhood ocular genetic diseases Nizamudheen, Vahitha Shameem

Abstract

Aniridia and Usher syndrome 1D are rare congenital defects that lead to vision loss in childhood. Here we tested several different approaches to treat animal models of these diseases. Aniridia is a pan-ocular condition caused by deletion or mutation of the PAX6 gene itself or by downstream intragenic abnormalities. We tested two approaches to target the aniridic-glaucoma phenotype in the Pax6Sey/+ mouse model of aniridia. First, since Tgfβ2 is a direct downstream target of Pax6, we tested whether injection of Tgfβ2-secreting mesenchymal stem cells into the Pax6Sey/+ mouse eye could improve development of anterior segment tissue abnormalities. We observed complete formation of Schlemm’s canal (SC) and a partially repopulated trabecular meshwork (TM). Secondly, we tested whether nonsense suppression strategy could rescue the TM defect in the mouse model harboring a nonsense mutation. Either an aqueous suspension of Ataluren® was injected subcutaneously, or topical eyes drops were instilled twice daily from P5 - P45. We found improved structural anatomy, and increased levels of Tgfβ2, Pitx2 and Foxc1 proteins. Furthermore, nonsense suppression via the topical route rescued the developmental defects of TM and SC better than by systemic treatment. Usher syndrome 1D (USH1D) is an autosomal-recessive condition characterized by deafness, vestibular dysfunction and vision loss caused by absence of CDH23 protein. We obtained a mouse model Y2209X line (Cdh23mtblr+/-) which carries a Cdh23 nonsense mutation. Homozygous Cdh23 mice show profound head shaking, circling behavior, deafness, and reduced ERG response. Here, we used prenatal and postnatal nonsense suppression with Ataluren®. We observed a reduction in severity of phenotypic features in Ataluren-treated mice compared to mock-treated mice as well as corrected localization of photoreceptor proteins. We also studied ex-vivo nonsense suppression therapy in Usher patient-specific cells. Induced pluripotent stem cells (iPSCs) were derived from a patient’s blood cells and three-dimensional (3D) retinal eyecups were generated in culture. The retinal eye cups were treated with Ataluren® which restored CDH23 protein levels, as well as other photoreceptors proteins including arrestin, recoverin and S-opsin. These results suggest patient-derived retinal eyecups are a useful tool for preclinical testing of small molecule drugs.

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