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O. V. Bulgakov, X. Liu, B. Pawlyk, M. Adamian, X. Xu, M. A. Sandberg, S. Khani, T. Li; Replacement Gene Therapy Preserves Photoreceptor Function And Survival in a Mouse Model of Retinal Degeneration Lacking Tulp1. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5348. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Tubby-like protein 1 (TULP1) is a photoreceptor specific protein expressed in both rods and cones. Mutations in Tulp1 cause retinitis pigmentosa and Leber congenital amaurosis in humans. A knockout mouse model lacking Tulp1 (TULP1-/-) develops rapid photoreceptor degeneration with severe mislocalization of rod and cone opsins. This study evaluated the efficacy of AAV-mediated gene replacement therapy in TULP1-/- mice.
Human and mouse TULP1 cDNAs were placed downstream of a human rhodopsin kinase promoter, known to drive expression in both rods and cones, and packaged into an AAV2/5 vector. Mice were given a subretinal injection at postnatal day 14 in one eye of either human or mouse TULP1 vector. Fellow eyes received a GFP control vector. Mice were evaluated at 3 months post-injection by electroretinography, immunofluorescence, light microscopy, and immunoblotting analysis for TULP1 protein expression, rod and cone opsin localization and photoreceptor rescue.
Immunofluorescence confirmed vector-mediated TULP1 expression in photoreceptor cell bodies, similar to endogenous TULP1 in wildtype mice. Immunoblotting demonstrated both mouse and human TULP1 proteins of correct molecular weights and levels of expression comparable to endogenous TULP1 in wildtype mice. Compared to the controls, treated eyes showed significantly greater functional preservation, increased cell survival, and an apparent reversal of the opsin mislocalization defect. By all measures, the mouse TULP1 construct had a much greater therapeutic efficacy than the human TULP1 construct.
AAV-mediated delivery of mouse and human TULP1 drives their efficient expression in photoreceptors and produces a significant therapeutic benefit in TULP1-/- mice. Future efforts to optimize TULP1 gene therapy should attempt to turn on the transgene expression sooner, given the rapid course of disease in this mouse model. The lesser efficacy of human TULP1 construct likely reflects the significant sequence divergence between TULP1 proteins of human and mouse origins (77% identity), rather than being predictive of a lesser efficacy in human patients.
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