The work targets a leading delivery method for the therapies, adeno-associated virus (AAV), and recently was published in the journal by UofL’s Maureen A. McCall and her colleagues from Harvard University and its Wyss Institute.

AAV is used in treating a number of conditions, including the retinal diseases McCall studies at UofL. However, it also has been known to cause serious side effects, such as elevated immune response and inflammation.

“It’s a real problem since there’s no real control,” said McCall, the Kentucky Lions Eye Research Endowed Chair and a professor in the Departments of Ophthalmology and Visual Sciences and Anatomical Sciences and Neurobiology. “Even with the best-laid plans, you see some inflammatory retinal response, and the amount can vary widely, including dangerous levels.”

The new research focuses on the role of the viral capsid, a component in AAV that’s believed to cause this response. Parts of the viral capsid interact with a protein known as Toll-like receptor 9 (TLR9), which senses foreign DNA in the body. TLR9 triggers the immune response, which causes inflammation and can reduce or eliminate the therapy’s effects.

“So, the hypothesis was that if you could change that capsid code and mask it from the Toll-like receptor, that you could build a better delivery tool,” McCall said.

The idea is to “cloak” the deleterious part of the capsid with a series of synthetic DNA “inflammation-inhibiting oligonucleotide” sequences meant to stop TLR9’s reaction. In mouse models, the researchers saw a 95% reduction in inflammation.

In many cases, gene therapies for optical diseases are delivered through the retina since the blood-retina barrier helps to mitigate some of the immune response. Ying Kai Chan, a former postdoctoral fellow in George Church’s group at the Wyss Institute, reached out to McCall in 2018 to partner on this work because of her research expertise and the experience of her UofL colleagues with these injections, especially Wei Wang, assistant professor of ophthalmology.

McCall’s work at UofL specifically focuses on the use of gene therapies to treat retinal diseases, including retinitis pigmentosa and other conditions that eventually can cause blindness. For some of these conditions, there is no known cure and many therapies are still in development and clinical trials. McCall said eliminating side effects associated with AAV delivery gets researchers one step closer to successful treatment.

“Solving this key problem with delivery is huge,” she said. “These therapies show promise in significantly increasing people’s quality of life. My hope is that one day we can use these therapies to slow – or even stop – the progression of these diseases and restore sight.”

Ophthalmology researchers at the University of Louisville have discovered the loss of vision in RP is the result of a disruption in the flow of nourishing glucose to the rods and cones. This disruption leads to the starvation of the photoreceptors.

In research published today in , the researchers, led by Douglas C. Dean, PhD, and Wei Wang, MD, PhD, of the UofL Department of Ophthalmology and Visual Sciences, described metabolic changes that result in the reduced availability of glucose in the cells.

As research provides a better understanding of the progression of RP, this knowledge may lead to therapies that could slow or stop this process before the rods and cones are destroyed. In addition to the relevance for RP, the researchers discovered the failure in glucose metabolism in RP is similar to changes seen in lung cancer and may be useful in developing therapeutic targets for both diseases.

“Interestingly, these metabolic changes appear similar to those we also are investigating in other studies into lung cancer in the laboratory,” Dean said. “Both lung cancer and neurons in the retina use glucose as a primary source for their metabolism. Attacking glucose utilization is a major strategy in fighting lung cancer. This unexpected connection in retinal and lung cancer metabolism has led us to link these seemingly unrelated systems to search for common drugs that target both lung cancer and retinal degeneration.”

RP is an inherited disease in which the photoreceptor cells in the retina – rods and cones – deteriorate over time. Photoreceptors absorb and convert light into electrical signals, which are sent through the optic nerve to the brain. Rods, located in the outer regions of the retina, allow peripheral and low-light vision. Cones, located mostly in the central part of the retina, allow perception of color and visual detail.

In RP, rods deteriorate first, causing the peripheral and low light vision loss typically associated with the disease. In later stages, the cones also deteriorate. Without cone function, RP patients lose the high-resolution daylight vision necessary for reading, facial recognition and driving. As a result, this stage of RP vision loss is more debilitating than the loss of nighttime or peripheral vision. RP affects 1 in 4,000 people globally.

This research is supported by grants from the National Eye Institute, BrightFocus Foundation and Research to Prevent Blindness.

The research, conducted by Kaplan, chair of the Department of Ophthalmology and Visual Sciences, Douglas Dean, PhD, and Wei Wang, PhD, and published in December in , could lead to therapies for preserving or recovering central vision in patients with RP. Kaplan will present the research findings at five conferences in the United States and abroad beginning this month.

Retinitis Pigmentosa is an inherited disease in which the photoreceptor cells in the retina – rods and cones – deteriorate over time. Photoreceptors absorb and convert light into electrical signals, which are sent through the optic nerve to the brain. Rods, located in the outer regions of the retina, allow peripheral and low-light vision. Cones, located mostly in the central part of the retina, allow perception of color and visual detail.

In RP, rods deteriorate first, causing the peripheral and low light vision loss typically associated with the disease. In later stages, the cones also deteriorate. Without cone function, RP patients lose the high-resolution daylight vision necessary for reading, facial recognition and driving. As a result, this stage of RP vision loss is more debilitating than the loss of nighttime or peripheral vision. RP affects 1 in 4,000 people globally.

Recent research has shown that as the rods deteriorate, the cones are no longer able to access glucose, which becomes trapped in the retinal pigment epithelium (RPE). As a result of glucose starvation, the cones go dormant and eventually die.

The UofL researchers found that the cones remain dormant for a period of time before they are completely lost, and if the glucose supply can be replenished during dormancy, the cones can be regenerated. The researchers were able to successfully restore cone access to glucose in either of two procedures. First, by transplanting rod-specific induced pluripotent stem cells beneath the retina, and second by injecting glucose directly into the subretinal space.

“Following rod stem cell transplant, we observed reassembly of the cone inner segments, regeneration of cone outer segments and increased electrophysiologic function within 1,000 microns from the transplant margin for at least three months after the transplantation in all directions,” Kaplan said. “However, the recognition that glucose starvation of cones occurred because of the trapping of glucose in the RPE provides multiple new possible treatments to restore lost central vision including drug therapy, gene editing and regenerative medicine.”

Kaplan will present these findings at the 6^th China Ocular Microcirculation Society Annual Meeting – International Ophthalmology Conference, Beijing, China, and the American Society of Retina Specialists, Boston, this month, at the Indiana Academy of Ophthalmology, Carmel, in September, the Retina Society, Boston, in October, and the 5th World Integrative Medicine Congress, Guangzhou, China in December.

This research has the potential to lead to therapies that preserve or restore central vision for individuals with RP.

“If therapy can prevent or reverse the onset of cone degeneration within the macula, most patients would be immeasurably helped and able to live a normal life despite the loss of peripheral vision and decreased dark adaptation,” Kaplan said.