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Emilia A Zin, Daisy Han, Jennifer Tran, John Gerard Flannery; AAV delivery of progranulin to retinas of progranulin-null mice is time-sensitive. Invest. Ophthalmol. Vis. Sci. 2021;62(8):1199.
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Neuronal ceroid lipofuscinosis (NCL) is a family of neurodegenerative lysosomal storage diseases. NCL type 11 (CLN11) is caused by biallelic mutations to the progranulin gene, leading to seizures, ataxia and vision loss. Patients and a murine model (PGRN-/-) show retinal thinning, accumulation of autofluorescent lipofuscin, and increase in microglial activation. As a recessive neurodegenerative disease, CLN11 is an ideal candidate for gene replacement therapy; however, both brain and retina require AAV gene delivery. This study aimed to deliver two different AAV constructs, 7m8-scCAG-PGRN and AAV92YF-scCAG-PGRN, to the retinas of PGRN-/- mice at four different timepoints, with the objective of stalling retinal degeneration.
Plasmids were packaged into two different capsids (7m8 and AAV92YF) using the triple transfection method and titered via qPCR. PGRN-/- cohorts received intravitreal injections of 7m8-scCAG-PGRN in one eye and PBS in the contralateral eye at different timepoints: 1, 6, and 12 months old. Mice that received AAV92YF-scCAG-PGRN were intravenously injected at post-natal day 3 or 4 (P3-4). At 12 months old, cohorts injected at P3-4, 1 and 6 months old had their retinas imaged by optical coherence tomography (OCT) and were enucleated. The cohort injected at 12 months old were imaged and enucleated at 18 months old. Retinal thickness was measured using OCT cross-sections. Retinas were cryosectioned and immunohistochemistry was performed. Lipofuscin was quantified through fluorescent imaging.
Animals that received AAV92YF-scCAG-PGRN showed a statistically significant improvement in overall retinal thickness and in photoreceptor layer thickness. However, animals injected with 7m8-scCAG-PGRN at month 1 and 6 showed no improvement in retinal thickness, while animals injected at 12 months old showed retinal thinning in comparison to contralateral controls. All cohorts show improvements in lipofuscin deposits when expressing PGRN.
Animals receiving PGRN at the earliest timepoint (P3-4) show improvement in retinal thickness, while the oldest cohort (12 months old) show retinal thinning when expressing PGRN. This points to a potentially toxic effect of PGRN delivery in elderly animals, which are reportedly more immune-reactive than age-matched wild-type mice. However, reduction in lipofuscin deposits indicate an improvement in lysosomal function, regardless of cell loss.
This is a 2021 ARVO Annual Meeting abstract.
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