UW Scientists Pursue Gene Therapy to Regenerate Lost Cells Required for Vision
According to the World Health Organization, more than two billion people worldwide suffer from some form of vision impairment, with approximately half of those caused by diseases that affect the nervous tissue responsible for light-detection i.e. the retina. Diseases such as age-related macular degeneration, glaucoma, and diabetic retinopathy cause the gradual death of retinal neurons and as a result impair our ability to see. While there are medical treatments to slow the loss of retinal neurons, there are no medical strategies to replace the neurons that were lost and hopefully restore vision. Therefore, the ability to regenerate neurons would represent a significant breakthrough for patients.
In order to regenerate neurons, doctors would need to shift the natural wound healing responses in the retina to a regenerative response, by instructing a specialized cell type in the retina to make new neurons instead of forming a scar.
Recently, scientists at the University of Washington and elsewhere have shown in genetically modified mice (transgenic mouse) that it is possible to induce specialized cells in the retina (Müller glia) to proliferate and give rise to neurons after an injury to the retina. One research team at the forefront of this effort is led by Tom Reh, PhD, a UW professor of Neurobiology and Biophysics and a faculty member in the Institute for Stem Cell and Regenerative Medicine (ISCRM).
Findings from studies by the Reh Lab and others have been encouraging. The challenge for the field now is to decipher which messages (genes) are necessary to generate specific neuron classes and to design a clinically safe and effective method to deliver said genes to the Müller glia in order to stimulate their regenerative response. New research from the Reh Lab, featured on the cover of the journal EMBO Molecular Medicine, details exciting progress on both fronts.
Dr. Reh is the senior author of the study. Marina Pavlou, PhD, a postdoctoral researcher in the Reh Lab, is the first author. “In previous work we have shown that it is therapeutically possible to shift Müller glia into neurons even after neurons have died in disease models of outer or inner retinal damage,” explains Dr. Pavlou. “In this paper, we wanted to build on this foundation and bring this strategy closer to clinical application.”
In 2022, Pavlou received funding through the ISCRM Fellows Program that supported early stages of the research detailed in the new study, helped her gather data necessary for the next phase of her multiyear effort, and led to additional fellowships from the Weill Neurohub Foundation and the Washington Research Foundation.
One promising way to deliver genes in live tissues is using viral vectors, specifically adeno-associated viral (AAV) vectors. In this approach, genetic material is carried by a harmless virus to its destination in the body. The FDA has already approved the use of AAV vectors to carry DNA to the retina to treat specific genetic diseases. As this method for gene delivery is well established, several groups have attempted to diversify the vector cargo in order to not only preserve existing neurons but also stimulate the growth of new neurons. However, closer inquiry revealed that the strategies implemented so far were confounded by off-target expression of AAV-delivered genes in existing neurons, without solid proof of new cells being made.
Pavlou summarizes the goal of the recently published study. “It was evident that the field needed to take a step back from an all-in-one vector approach and generate concrete evidence that it is possible to induce neurogenesis when you deliver proneural genes to Müller glia by AAV vectors. We were determined to show in a meticulous way that we can permanently label Müller glia that received proneural genes delivered by AAV and trace their transition into neurons using several complementary methods.”
In their study, Pavlou et al used a genetically engineered mouse, in which Müller glia express a molecule that can recombine DNA and permanently label cells with a red fluorescent reporter that allows researchers to trace them and their progeny. These mice received different versions of AAV vectors in their eyes, where each vector carried genetic information that required recombination in Müller glia before becoming active. This meant that although AAV vectors could penetrate any cell in the retina, their cargo would only become active in the Müller glia, whose response could then be monitored thanks to their permanent label.
Pavlou and her colleagues used histology, single-cell RNA sequencing and electrophysiological profiling to verify that the genes delivered by AAV vectors were indeed pushing Müller glia to become neurons. They showed that AAV delivery of different proneural genes could stimulate the genesis of distinct neuronal subtypes, and that this shift in cell fate followed a similar path to the group’s previous observations in different mouse models.
The work continues in the Reh lab. Pavlou is now focused on expanding this work in non-human primates and establishing an approach that is only based on AAV vectors for clinical application. With regards to the current paper, she emphasizes the collaborative nature of the investigation “This work has been an incredible group effort supported by great people and great scientists. We believe the results we produced are an important step forward for regenerative medicine in ophthalmology.”