Scientists restore sight in mice using a new gene-editing technique

Scientists in China have effectively treated retinitis pigmentosa, a leading cause of vision loss, in mice, according to a press release published in Eurekalert.

The research team utilized a novel form of CRISPR-based genome editing that is exceptionally adaptable and could potentially remedy numerous genetic mutations responsible for causing different diseases.

Scientists have employed genome editing to restore vision in mice affected by genetic disorders such as Leber congenital amaurosis affecting the retinal pigment epithelium, a non-neuronal cell layer in the eye that supports the light-sensing rod and cone photoreceptor cells.

Nonetheless, most inherited forms of blindness, including retinitis pigmentosa, arise from genetic anomalies in the neural photoreceptors instead of the retinal pigment epithelium.

“The ability to edit the genome of neural retinal cells, particularly unhealthy or dying photoreceptors, would provide much more convincing evidence for the potential applications of these genome-editing tools in treating diseases such as retinitis pigmentosa,” says Kai Yao, a professor at the Wuhan University of Science and Technology.

PESpRY: A highly adaptable CRISPR system

Retinitis pigmentosa is estimated to affect one in 4,000 people and can result from mutations in more than 100 different genes. This condition first affects the rod cells responsible for sensing dim light, causing their dysfunction and death. Subsequently, it can also affect the cone cells required for color vision, eventually leading to irreversible vision loss that is severe in nature.

Yao and his research team aimed to restore the vision of mice affected by retinitis pigmentosa resulting from a mutation in the gene responsible for encoding the critical enzyme PDE6β. They accomplished this by creating a highly adaptable CRISPR system called PESpRY, which can be customized to correct various types of genetic mutations present anywhere within the genome.

By targeting the PDE6β gene mutation with the PESpRY system, Yao and the team were able to effectively correct the mutation and restore the enzyme's activity within the retinas of mice suffering from retinitis pigmentosa. This intervention prevented the degeneration of rod and cone photoreceptor cells, and their electrical reactions to light was reinstated.

The researchers subjected the gene-edited mice to various behavioral tests, which demonstrated that the animals retained their vision well into their old age. For instance, they were able to navigate through a water maze guided by visual cues almost as proficiently as healthy mice, and their typical head movements in response to visual stimuli were exhibited.

Yao emphasizes that additional work is necessary to ensure the safety and effectiveness of the PESpRY system in humans. Nevertheless, the study provides substantial evidence for the applicability of this innovative genome-editing strategy in vivo and its potential for treating diverse research and therapeutic contexts, particularly inherited retinal diseases such as retinitis pigmentosa.

The study was published in the Journal of Experimental Medicine.

Study abstract:

Retinitis pigmentosa (RP) is an inherited retinal dystrophy causing progressive and irreversible loss of retinal photoreceptors. Here, we developed a genome-editing tool characterized by the versatility of prime editors (PEs) and unconstrained PAM requirement of a SpCas9 variant (SpRY), referred to as PESpRY. The diseased retinas of Pde6b-associated RP mouse model were transduced via a dual AAV system packaging PESpRY for the in vivo genome editing through a non-NGG PAM (GTG). The progressing cell loss was reversed once the mutation was corrected, leading to substantial rescue of photoreceptors and production of functional PDE6β. The treated mice exhibited significant responses in electroretinogram and displayed good performance in both passive and active avoidance tests. Moreover, they presented an apparent improvement in visual stimuli-driven optomotor responses and efficiently completed visually guided water-maze tasks. Together, our study provides convincing evidence for the prevention of vision loss caused by RP-associated gene mutations via unconstrained in vivo prime editing in the degenerating retinas.