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R. Kumar-Singh, S. P. Read, S. M. Cashman; POD DNA Nanoparticles Rescue an Adult Mouse Model of Retinal Degeneration. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3108.
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POD, or "Peptide for Ocular Delivery," is a novel synthetic cationic cell penetrating peptide (CPP) which when modified by addition of a polyethylene glycol moiety (PEG-POD) can be used to compact plasmid DNA into 120-150 nm nanoparticles. These nanoparticles can transfect the retinal pigment epithelium (RPE) following delivery to the subretinal space of adult mice. To test the physiological relevance of PEG-POD mediated gene delivery, PEG-POD DNA nanoparticles carrying a transgene expression cassette coding for Glial-cell line Derived Neurotrophic Factor (PEG-POD~GDNF) were examined for their ability to rescue photoreceptors in a light induced model of retinal degeneration.
Four days following subretinal delivery of PEG-POD~GDNF, PEG-POD~Lux (nanoparticles expressing a luciferase transgene) or buffer alone, retinal degeneration was induced by exposure of mice to bright blue light for 4 hours. Expression of GDNF was confirmed using RT-PCR. Apoptosis was quantified by both TUNEL and nucleosome release ELISA. Anatomical and functional rescue was measured at 7 and 14 days post-light exposure by quantification of the outer nuclear layer (ONL) thickness and by electroretinogram (ERG), respectively.
Retinas injected with PEG-POD~GDNF showed a significant (~7-fold) decrease in the number of TUNEL positive cells in the ONL relative to those injected with either PEG-POD~Lux (p<0.005) or buffer (p<0.0005). Nucleosome release assay confirmed this reduction in apoptosis (~3.1-fold) in PEG-POD~GDNF injected eyes relative to both controls (p<0.05). The average ONL thickness of the superior retina in PEG-POD~GDNF injected eyes was ~31.5% greater at 7 days post-light treatment relative to PEG-POD~Lux (p<0.01) or buffer alone (p<0.0005) and ~26% greater than either control injection at 14 days post-light treatment (p<0.05). When examining the functional response of the retina to light by ERG, PEG-POD~GDNF injected eyes exhibited a 32-39% increase in amplitude in the a-wave (p<0.05) and a 27-31% increase in the b-wave amplitude (p<0.05) relative to controls after light treatment.
This is the first study demonstrating histological and functional rescue of an adult model of retinal degeneration using a non-viral approach. Though expression is short lived for application in the clinic, this study represents an important step in the development of non-viral gene therapy for retinal diseases.
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