Total RPE65 Protein Levels Doubled in Mice with RP

A recent study, published in Human Gene Therapy, has revealed fascinating findings regarding the total RPE65 protein levels in mice affected by autosomal dominant retinitis pigmentosa. The study demonstrated a remarkable doubling of these protein levels after the subretinal delivery of adeno-associated virus (AAV)-RPE65 gene supplementation.

This research offers promising insights into the potential therapeutic benefits of gene supplementation for individuals with retinitis pigmentosa.

In the study conducted by Debra Thompson and coauthors from the University of Michigan Medical School, gene supplementation was evaluated in mice with a monoallelic mutation that encodes a rare D477G RPE65 variant, known as D477G KI mice. These mice exhibited decreased levels of total RPE65 protein due to the heterozygous mutation. Following the treatment, the introduced recombinant RPE65 was found to specifically localize to the retinal pigment epithelium and remained stable for a minimum of 6 months after the injection.

HPLC analysis of dark-adapted and light-adapted heterozygous

HPLC analysis of dark-adapted and light-adapted heterozygous D477G KI mice showed similar levels of chromophore in eyes that received AAV-RPE65 or PBS or were uninjected, whereas recovery of 11-cis retinal at 2 h post bleaching was significantly increased only in eyes that received AAV-RPE65. (A) 11-cis retinal and (B) all-trans retinal, quantified as the sum of syn- and anti-retinal oximes, in eyes from mice at 6–8 months postinjection and uninjected controls that were dark-adapted, bleached, and recovered in the dark for 2 or 4 h. AAV-RPE65, filled yellow bars; uninjected, open bars (n = 5). PBS injected, filled gray bars; uninjected, open bars (n = 7). (C) Representative HPLC chromatograms. *p = 0.013, **p = 0.003. 11cRAL OX, 11-cis-retinal oxime; atRAL OX, all-trans-retinal oxime; BL, bleached; DA, dark-adapted; HPLC, high-performance liquid chromatography; PBS, phosphate-buffered saline; Rec, recovered.

In addition, the investigators reported that "rates of recovery of the chromophore 11-cis retinal after bleaching were significantly increased in eyes that received AAV-RPE65, consistent with increased RPE65 isomerase activity." Furthermore, they emphasized: "It remains of significant interest to determine whether increase RPE65 expression can reduce the disease burden associated with D477G RPE65."

"While patients with inherited retinal dystrophy due to RPE65 deficiency can benefit from the FDA approved gene therapy, it has been very unclear whether patients with autosomal dominant retinitis pigmentosa due to the D477G RPE65 mutation could be treated in a similar way," says Editor-in-Chief Terence R. Flotte, MD, Celia and Isaac Haidak Professor of Medical Education and Dean, Provost, and Executive Deputy Chancellor, University of Massachusetts Chan Medical School.

This study, in its preliminary stage, offers crucial proof-of-principle data supporting the use of gene supplementation as a potential treatment for patients affected by this specific mutation.

Reference

Kecia L. Feathers et al, Gene Supplementation in Mice Heterozygous for the D477G RPE65 Variant Implicated in Autosomal Dominant Retinitis Pigmentosa, Human Gene Therapy (2023). DOI: 10.1089/hum.2022.240

Gene Therapy Breakthrough: Total RPE65 Protein Levels Doubled in Mice with RP

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