DNA editing in mice helps prevent blindness

Using a revolutionary genome editing tool titled CRISPR-Cas9 in mice, scientists at the Institute for Basic Science’s Center for Genome Engineering have developed a less invasive treatment for preventing blindness.

CRISPR-Cas9 is used to edit DNA by adding, removing or altering parts of the DNA sequence. In this process scientists identify a portion of the DNA they wish to alter. They then design a guide RNA (gRNA) sequence of approximately 20 nucleotide bases that are complementary to the bases at the location of interest. The gRNA then binds to that section of DNA and “guides” Cas9, an enzyme, to the predesignated area.

This Cas9 enzyme can then cleave the double-stranded DNA, allowing DNA to be added or removed at this location. The cell will then naturally attempt to repair the cut DNA, effectively “closing” the cut and rejoining strands together.

Due to CRISPR-Cas9’s ability to directly modify genes, it is typically used to correct mutations responsible for hereditary diseases. However scientists in the Center for Genome Engineering study have harnessed its power to develop a new potential treatment for non-hereditary blindness.

By modifying genes in tissues necessary for retinal health in mice through this “gene surgery,” as scientists at the Center for Genome Engineering have described it, it is possible to treat age-related macular degeneration (AMD).

Those afflicted by the degenerative disease, which affects about one in every ten people over the age of 65, often see blind spots and suffer from distorted vision.

AMD is caused by an excessive secretion of vascular endothelial growth factor (VEGF) from retinal pigment epithelium cells, which in turn induces leakage of blood and fluid into the eye. This can then damage the macula, an area in the center of the retina.

Currently, AMD treatments consist of at least seven anti-VEGF injections per year.

However, the treatment addresses only the effects of the VEGF overexpression. With the study’s new CRISPR-Cas9 technique, scientists hope to introduce less invasive and longer-lasting therapies to patients.

In the study, scientists used CRISPR-Cas9 to modify the VEGF gene in mice with wet AMD (a more severe type of AMD) via injection. As predicted, only the VEGF gene was affected. To assess the efficacy of the treatment, researchers then monitored choroidal neovascularization, or the formation of new blood vessels in the eye (a common issue in wet AMD).

They discovered a 58 percent decrease in the area of the eye expected to suffer from choroidal neovascularization in normal wet AMD progression.

In addition, scientists noted that cone dysfunction, another side effect of wet AMD that typically occurs within three days, was absent a week after the treatment.

The study shows promise for future treatments of diseases both hereditary and non-hereditary for both children and adults.

“We envision that, in the future, surgeons will be able to cut and paste disease-causing genetic elements in patients,” Kim Jin-Soo, director of the Center for Genome Engineering, said in a press release.

Now that the method has been proven effective in mice, the Center for Genome Engineering plans to continue preclinical trials in order to confirm the efficacy of CRISPR-Cas9 treatments for humans.