CRISPR gene editing promising for blinding disease retinitis pigmentosa

National Eye Institute-funded scientists using gene editing corrected a mutation in a mouse model of retinitis pigmentosa, an inherited blinding eye disorder. The gene editing strategy restored production of rhodopsin, a sensory protein crucial for vision, and led to improvements in retinal function and structure. The findings published online November 18 in the Proceedings of the National Academy of Sciences.

Gene editing restored the production of rhodopsin in the photoreceptor outer segments, and preserved the thickness of the outer nuclear layer, where photoreceptor nuclei are located. Credit: Biorender

"Further development of this gene editing approach may expand treatment options for patients with inherited retinal diseases caused by mutations in rhodopsin for which there are currently no treatments," said the study's lead investigator, Krzysztof Palczewski, Ph.D., Irving H. Leopold Chair of Ophthalmology and distinguished professor, University of California, Irvine School of Medicine. The study was conducted in collaboration with the lab of David R. Liu, Ph.D. at the Broad Institute of MIT and Harvard.

Vision depends on the function of light-sensitive neurons in the retina called rod and cone photoreceptors. Rods are crucial for night vision; cones are important for daytime vision and perceiving color. Packed into the outer segments of photoreceptor cells are light-sensitive proteins called opsins that capture photons of light and convert them into electrical signals that the brain deciphers as vision.

Rhodopsin, the type of opsin in rod photoceptors, also plays a major structural role. In diseases like retinitis pigmentosa, mutations in the genetic instructions for making rhodopsin impair the structure and function of rod photoreceptors, which leads to rod photoreceptor death and vision loss.

Using a CRISPR-Cas9 tool called base editing, a gene editing strategy capable of precisely targeting and replacing specific DNA sequences, the researchers edited a rhodopsin-150K mutation in a mouse model of retinitis pigmentosa. In people, rhodopsin-150K mutations cause a rare, autosomal recessive form of disease, which is inherited by a child who receives the mutated gene from each parent.

"The selection of an autosomal recessive form of the disease, we reasoned, would allow us to achieve a therapeutic rescue from reasonably efficient editing. In a clinical setting, correction of even a subset of rod photoreceptors could potentially stop the progression of retinal degeneration and provide some benefit to patients," said Palczewski.

The gene editing strategy productively edited up to 44% of the rhodopsin gene product in the treated mice.

Compared with untreated mice, those treated within 15 days of birth had modest improvements in retinal function, according to electroretinography, which measures photoreceptor responses to light. Mice treated after 15 days were found to have retinal degeneration that was too far gone to be rescued by the gene editing approach.

The investigators are hopeful they can improve gains in retinal function by optimizing dosing and improving surgical technique, noting in their report that the effect of treatment was uneven across the retina.

The gene editing treatment also prevented the loss of a retinal tissue layer called the outer nuclear layer, which contains the nuclei of rod and cone photoreceptors.

The rescue of rod photoreceptors in retinitis pigmentosa is expected to also improve the function of cone photoreceptors, as rods support the health of cones.

The study was funded by the NEI grants R01EY009339, R01EY034501, F30EY033642, F30EY029136, and P30EY034070.

Reference

Du SW, Newby GA, Salom D, Gao F, Menezes CR, Suh S, Choi EH, Chen PZ, Liu DR, Palczewski K. "In vivo photoreceptor base editing ameliorates rhodopsin-E150K autosomal-recessive retinitis pigmentosa in mice." Published online November 18, 2024, PNAS. https://doi.org/10.1073/pnas.2416827121

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