Correction of night blindness in dogs

People with congenital stationary night blindness (CSNB) cannot distinguish objects in low light conditions. This disability presents challenges, especially when there is no artificial lighting or when driving at night.

In 2015, researchers at Penn’s School of Veterinary Medicine learned that dogs can develop an inherited form of night blindness with great similarities to the disease in humans. In 2019, the team identified the gene responsible.

Today in the magazine Proceedings of the National Academy of Sciences, reported a breakthrough: a gene therapy that restores night vision in dogs born with CSNB. The success of this approach, which is aimed at a group of deep retinal cells called bipolar ON cells, represents an important step towards the goal of developing a treatment for dogs and people with disease, as well as other vision problems involving ON. function of bipolar cells.

Dogs with CSNB who received a single injection of gene therapy began to express the healthy LRIT3 protein in their retinas and were able to navigate a maze with low light skill. The treatment also seems long-lasting, with a sustained therapeutic effect lasting a year or more.

“The results of this pilot study are very promising,” says Keiko Miyadera, lead author of the study and assistant professor at Penn Vet. “In people and dogs with congenital stationary night blindness, the severity of the disease is constant and does not change throughout their lives. And we were able to treat these dogs as adults, between 1 and 3 years old. The results are promising and relevant to the human patient population, as we could theoretically intervene even in adulthood and see improved night vision. ”

In previous work, the Penn Vet team, working with groups in Japan, Germany, and the United States, discovered a population of dogs with CSNB and determined that mutations in LRIT3 nothing was responsible for the deterioration of night vision in dogs. The same gene has also been implicated in some cases of human CSNB.

This mutation affects the function of bipolar ON cells, but unlike some blinding diseases, the overall structure of the retina as a whole remained intact. This gave the research team hope to provide a normal copy of the document LRIT3 The gene can restore night vision in affected dogs.

Although Penn Vet researchers in the Division of Experimental Retinal Therapies have developed effective gene therapies for a variety of other blinding disorders, none of these previous treatments have targeted bipolar ON cells. located deep in the midline of the retinal layer.

“We’ve gotten into the retinal nobody’s land with this gene therapy,” says William A. Beltran, co-author and professor at Penn Vet. “This opens the door to the treatment of other diseases that affect bipolar ON cells.”

Researchers overcame the obstacle of targeting these relatively inaccessible cells with two key findings. First, through a rigorous screening process conducted in collaboration with colleagues at the University of California at Berkeley, led by John Flannery and the University of Pittsburgh led by Leah Byrne, they identified a vector for health. LRIT3 gene that would allow the treatment to reach the target cells. And second, they paired the healthy gene with a promoter, the genetic sequence that helps initiate the “reading” of the therapeutic gene, which would act in a specific way in the cell.

“The previous therapies we’ve worked on have been aimed at photoreceptors or cells in the retinal pigment epithelium,” says co-author Gustavo D. Aguirre, a Penn Vet professor. “But the promoter we use here is very specific for targeting bipolar ON cells, which avoids possible off-target effects and toxicity.”

Researchers suspect that the restoration function LRIT3 The gene allows signals to pass through photoreceptor cells to bipolar ON cells. ” LRIT3 is expressed at the “fingertips” of these cells, “says Beltran.” The introduction of this transgene essentially allows the two cells to shake hands and communicate again.

An open question is whether targeting both photoreceptor cells and ON bipolar cells could lead to even greater improvements in night vision. Other research groups studying these conditions in mice have targeted therapy to photoreceptor cells and found some vision that needs to be restored, suggesting a possible route to improve the effects of gene therapy.

And while therapy allowed for functional recovery: dogs could navigate a maze when their treated eye was exposed, but not when they were covered, healthy copy of the gene was only expressed in 30% of the cells. bipolar ON. In follow-up work, researchers hope to increase this adoption.

“We were very successful in this study, but we saw that some dogs were recovering better than others,” says Miyadera. “We would like to continue working to maximize the therapeutic benefit while ensuring safety. And we’ve seen this treatment last a long time, but is it for life after an injection? This is something we would like to know. »

The team also plans to modify the therapy to use the human version of the LRIT3 gen, a necessary step to translate treatment for people with CSNB with a possible clinical trial.

Miyadera, Beltran, and Aguirre co-authored the study with Evelyn Santana, Karolina Roszak, Sommer Ifrig, Yu Sato, Alexa Gray, Ana Ripolles Garcia, and Penn Vet’s Valerie Dufour; Simone Iwabe, Ryan F. Boyd and Joshua T. Bartoe of Charles River Laboratories; and the University of California, Meike Visel of Berkeley, John G. Flannery and Leah C. Byrne (now at the University of Pittsburgh).

Keiko Miyadera is an Assistant Professor of Ophthalmology in Penn Vet’s Department of Clinical Science and Advanced Medicine.

William Beltran is Professor of Ophthalmology in the Department of Clinical Sciences and Advanced Medicine at Penn Vet and Director of the Retinal Experimental Therapies Division.

Gustavo D. Aguirre is a professor of medical genetics and ophthalmology in Penn Vet’s Department of Clinical Science and Advanced Medicine.

The study was supported by the Margaret Q. Landenberger Research Foundation, National Eye Institute / National Institute of Health (Grant EY-006855), Fighting Blindness Foundation, Van Sloun Foundation for Canine Genetic Research and Sanford and Susan Greenberg End Blindness Outstanding Achievement Prize. .

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