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Wen-Tao Deng, Jie Li, Ping Zhu, Wolfgang Baehr, William Hauswirth; Successful rescue of M-cone function in aged M-opsin knock-out mice, a model for blue cone monochromacy. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3419. doi: https://doi.org/.
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Blue cone monochromacy (BCM) is an X-linked congenital disorder with severe cone dysfunction due to the absence of the long and medium wavelength-sensitive cone opsins. Previously we showed that AAV5-mediated expression of either human M- or L-opsin promoted regrowth of cone OS and rescued M-cone function in the treated M-opsin knockout (Opn1mw-/-) dorsal retina. In this study, we seek to determine cone viability and window of treatability in aged Opn1mw-/- mice.
We labeled retinal whole mounts of Opn1mw-/- mice of different ages with peanut agglutinin (PNA) to assess cone viability. AAV5 vector expressing human L-opsin driven by the cone-specific PR2.1 promoter was injected subretinally into one eye of 7- and 12-month old Opn1mw-/- mice, while the contralateral eyes remained untreated. M-cone mediated retinal function was analyzed 2- and 12- months post-injection by electroretinography (ERG) under middle wavelength conditions. L-opsin transgene expression and cone OS were examined by immunohistochemistry using antibodies against M/L-opsin, S-opsin, cone PDE6γ’ subunit, and cone arrestin.
We show that the numbers of positive PNA-stained cells were only slightly reduced in dorsal retinas of aged Opn1mw-/- mice, demonstrating that cone inner segments and cone sheaths remain intact and that the dorsal cones remain viable even in 16-month-old Opn1mw-/- mice. Consistent with this observation, AAV5-mediated expression of human L-opsin rescues M-cone function (60 ± 8 µV in treated eyes vs unrecordable in untreated, n=8, P < 0.005), and restores OS morphology in dorsal retinas of Opn1mw-/- mice treated at 12 months of age. We also show that M-cone function (45 ± 4 µV, n=8, P < 0.005) and structure rescue lasted for at least 12 months in Opn1mw-/- mice treated at 7 months of age.
Dorsal cones of Opn1mw-/- mice without visual pigments remain viable for at least 12 months and can still be functionally and structurally rescued by human cone opsin gene therapy. These results have important implications for BCM patient entry selection in any future BCM gene therapy clinical trial.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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