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FUTURE FILE: Highlighting innovative early-stage and preclinical concepts in retina

Future File is a Retinal Physician feature designed to highlight new and innovative early-stage and preclinical concepts that could one day advance the everyday practice of retina specialists.

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Elovanoids May Provide Retinal Cell Protection

■ Researchers led by Nicolas Bazan, MD, PhD, Boyd Professor and Director of the Neuroscience Center of Excellence at LSU Health New Orleans School of Medicine in New Orleans, Louisiana, found a new mechanism by which a class of molecules his lab discovered may protect brain and retinal cells against neurodegenerative diseases like macular degeneration and Alzheimer disease. Results, published online in PNAS, identify elovanoids as a potential new therapeutic approach for these devastating conditions.

“It is the first report that elovanoids are potential senolytic therapies because they target and dramatically arrest gene expression engaged in cell disturbances, including senescence gene programs and retina cell death in conditions that recapitulate retinal degenerative diseases,” notes Dr. Bazan. He added that because the retina is key to age-related macular degeneration and is an integral part of the nervous system, the reported discoveries are also applicable to Alzheimer disease and other neurodegenerative conditions.

In experimental models of AMD and Alzheimer disease, Bazan’s team found that elovanoids (bioactive chemical messengers made from omega-3 very long-chain polyunsaturated fatty acids) counteracted these processes. These novel compounds target senescence genes, a key senescence protein, and the expression of senescence-related genes in the retinal pigment epithelial cells. Elovanoids also restored the structure and integrity of both the retinal epithelial and photoreceptor cells after being damaged by amyloid beta. Overall, they foster repair, remodeling, and regeneration.

Acucela Releases Preclinical Data for Emixustat

■ Acucela, a clinical-stage ophthalmology company, announced the publication of encouraging preclinical data related to the company’s investigational drug candidate, emixustat hydrochloride (emixustat), in the journal Investigative Ophthalmology & Visual Science. Authors of the paper evaluated the effects of emixustat on retinal metabolism in rat models. In these animals, both oxygen consumption and ion channel activity in the retina were evaluated under dark conditions, when the retina is most metabolically active. Emixustat treatment resulted in decreased oxygen consumption and ion channel activity. The authors note that these data indicate that emixustat can reduce metabolic and oxygen demands in the retina under dark conditions, which has implications for the treatment of ischemic retinal diseases in which hypoxia plays a prominent role, such as diabetic retinopathy.

Retinal Cell Transplantation Studied

■ ProtoKinetix has completed an in vivo study to assess the effect of anti-aging glycoprotein (AAGP) on the long-term survival and functional activity of photoreceptor precursor cells (PPCs) in the animal ocular model of genetic retinal degeneration. The objective of this study was to determine the effect of 24-hour pretreatment with AAGP PKX-001 at 4 mg/mL on the long-term (3, 4.5, and 6 months) survival and functional activity of PPCs following their subretinal transplantation into the eye of nude immunocompromised rats with genetic retinal degeneration.

In vivo tests demonstrated that transplantation of PPCs pretreated with AAGP (PKX-001) results in statistically significant improvements in both the visual behavioral (optokinetic tracking test) and functional analysis (electroretinogram test) responses as compared with PPCs without pretreatment. Imaging data revealed that pretreatment of PPCs with AAGP also leads to a substantial enhancement of cell survival as determined at 3, 4.5, and 6 months after cell transplantation. At the 6-month time point, the AAGP-treated cells acquired the ability to express retinal and synaptic proteins, confirming that AAGP has no adverse effect on precursor cells’ maturation.

ProtoKinetix is a molecular biotechnology company that has developed and patented a family of stable, potent AAGP that enhance both engraftment and protection of transplanted cells, organs, and tissues used in regenerative medicine. Pluripotent stem-cell therapy guided into retinal cells could potentially cure blindness even in the late stages of disease, the company says. However, until now, studies in animals have shown that too few transplanted retinal cells survive the hostile local environment long enough to integrate correctly into the retina’s complex neural circuitry. The company says that the AAGP molecule in this study has overcome this obstacle for stem-cell treatments that aim to replace retinal cells. At the 5-month timepoint, additional tests showed that AAGP preserved and allowed these cells to mature without compromise. These studies are a critical component of the preclinical testing required to advance this program into clinical trials. The study is being conducted by the Gregory-Evans Retinal Therapeutic Lab at the University of British Columbia, Canada.

Brain Can Integrate Natural and Artificial Vision

■ When there is damage to the photoreceptor layers in the retina, an artificial retina, a device built from tiny electrodes smaller in width than a hair, may be implanted. Activating these electrodes results in electrical stimulation of the remaining retinal cells and results in visual restoration, albeit partially. Patients with age-related macular degeneration who are implanted with an artificial retina possess a combination of artificial central vision and normal peripheral vision. This combination of artificial and natural vision is important to study to understand how to help the blind. One of the critical questions in this regard is whether the brain can integrate artificial and natural vision properly.

In a new study published in the journal Current Biology, researchers from Bar-Ilan University in Ramat Gan, Israel, and Stanford University in Stanford, California, report for the first time the discovery of evidence indicating that the brain knows how to integrate natural and artificial vision, while maintaining processing information that is important for vision.

“We used a unique projection system which stimulated either natural vision, artificial vision, or a combination of natural and artificial vision, while simultaneously recording the cortical responses in rodents implanted with a subretinal implant,” said Tamar Arens-Arad, who conducted the experiments as part of her doctoral studies. The implant, developed by Daniel Palanker, PhD, at Stanford University, is composed of dozens of tiny solar cells and electrodes.

“These pioneering results have implications for better restoration of sight in AMD patients implanted with retinal prosthetic devices and support our hypothesis that prosthetic and natural vision can be integrated in the brain. The results could also have implications for future brain-machine interface applications where artificial and natural processes co-exist,” said Prof. Yossi Mandel, head of Bar-Ilan University’s Ophthalmic Science and Engineering Lab and the study’s lead author.

Genetic Variation Seen as a Cause of AMD

■ A study published in the journal Stem Cell Reports focused on the importance of a specific genetic variation that affects expression of the VEGFA gene. The product of this gene, the VEGFA protein, is known for supporting new blood vessel growth — a process that goes awry in AMD. Using this new model of AMD, the researchers determined that a specific genetic variation in a region of the genome that regulates expression of the VEGFA gene reduces the amount of VEGFA produced and directly contributes to AMD.

“We didn’t start with the VEGFA gene when we went looking for genetic causes of AMD,” said senior author Kelly A. Frazer, PhD, professor of pediatrics and director of the Institute for Genomic Medicine at UC San Diego School of Medicine in San Diego, California. “But we were surprised to find that, with samples from just 6 people, this genetic variation clearly emerged as a causal factor.”

The researchers said they were surprised that the causal variant results in decreased VEGFA expression prior to AMD onset, and this finding could potentially be relevant for the treatment of AMD using anti-VEGF therapeutics. The genetic variant most closely associated with AMD was rs943080, a specific genetic variation that affects expression of the VEGFA gene by altering activity of a distant region of the genome. Five of the 6 participants had 1 copy of rs943080 and 1 person had 2 copies of the gene variant.

Faulty Müller Cells Could Contribute to Macular Disease

■ Scientists have found significant differences in the shape and biology of the same type of cell taken from different parts of the retina, according to a study in the journal eLife. The results could help explain why the macula is more susceptible to disease than the peripheral retina and reveal a protective mechanism that may be disrupted in disease.

This study looked at Müller cells, the major glial cells of the retina that are present in both the macula and peripheral retina and play important roles in nerve-cell function, metabolism, and light-receptor activation in the eye. Recent reports suggest that Müller cells are the major production site for 2 essential amino acids — serine and glycine.

“The importance of Müller cells for normal retinal function suggests that their dysfunction contributes to many eye diseases, such as diabetic retinopathy and macular telangiectasia,” explains co-first author Ting Zhang, research fellow at the Save Sight Institute, University of Sydney, Australia. “But whether the function of Müller cells differs in the macula and the peripheral retina was previously unknown. We set out to investigate the features of Müller cells from these 2 locations, with a particular focus on their production of serine and glycine.”

The team isolated Müller cells in eye tissue provided by healthy donors and grew them in the lab to study the cells’ features. They found that Müller cells from the macula were small and spindle or star-shaped, while those from the peripheral retina were much larger and had multiple processes.

Analysis of the cells revealed 7,588 genes with different levels of expression between the 2 cell types. Moreover, activity of key genes related to serine production, such as the enzyme phosphoglycerate dehydrogenase (PHGDH), was higher in the macular Müller cells than in those from the peripheral retina. “This finding is particularly important because a recent study reported that the serine metabolic pathway may play an important role in macular telangiectasia through defects in PHGDH,” says co-first author Ling Zhu, also a research fellow at the Save Sight Institute.

Possible Pathway to Retinal Regeneration Identified

■ Researchers at Baylor College of Medicine, the Cardiovascular Research Institute, and the Texas Heart Institute revealed in the journal Cell Reports that although the mammalian retina does not spontaneously regenerate, it has a regenerative capacity that is kept dormant by a cellular mechanism called the Hippo pathway. The discovery opens the possibility of activating the retina’s ability to restore lost vision via this pathway.

Müller glial cells in injured mammalian retina do not restore vision as they have been proven to do in zebrafish, but previous research has shown that, when the mammalian retina is injured, a small subset of Müller glial cells takes the first steps needed to enter the proliferation cycle, such as acquiring molecular markers scientists expect to see in a proliferating cell. But the effect is transient and the cells soon shut off, leading Baylor researchers to believe a suppressing mechanism is responsible.

The researchers then focused their attention on the Hippo pathway, a network of molecular events that contributes to organ growth during development and to the regulation of heart tissue regeneration in response to myocardial infarction. In this study, the researchers first determined that the Hippo pathway is expressed in mammalian Müller glial cells. Then, they investigated whether altering the Hippo pathway in these cells would affect their ability to proliferate. Creating a malfunctioning Hippo pathway by eliminating two of its molecular steps resulted in modest cell proliferation. And when the researchers genetically engineered Müller glial cells to carry a version of YAP called YAP5SA that is impervious to the inhibitory influence of Hippo, the cells showed major proliferation and acquired a progenitor cell identity. Importantly, a small subset of the Müller glia-derived progenitor cells showed signs of spontaneous differentiation into new retinal neurons.

“Our next step is to develop a strategy to guide proliferating Müller glial cells into differentiation pathways leading to retinal cells capable of restoring vision,” said Dr. Ross A. Poché of the Baylor team.

Gene Therapy for Night Blindness

■ By identifying the location and mechanism of a key protein required for low-light vision, researchers at the University of Louisville and the Medical College of Wisconsin have shown that gene therapy may restore visual function for people with a form of congenital stationary night blindness. In mice models with genetic mutations similar to humans with night blindness, scientists used adeno-associated viruses to reintroduce the protein into cells in the retina.

The research recently was published in Cell Reports. Grants from the National Institutes of Health, Research to Prevent Blindness, and the Foundation Fighting Blindness funded the research.

“Our research shows that if you replace the missing protein using a gene therapy approach, you can restore visual function,” Ron Gregg, PhD, professor and chair of the Department of Biochemistry and Molecular Genetics at the University of Louisville School of Medicine, said in a university news release.

Humans are adept at seeing in low light, but genetic mutations can disrupt that ability, causing total night blindness. Proteins on the surface of photoreceptors ensure that visual signals pass from the photoreceptors to retinal bipolar cells. This is a crucial step in the transmission of visual information from the eyes to the brain. Genetic mutations disrupt the signal transfer between photoreceptors and retinal bipolar cells, impairing vision.

People with congenital stationary night blindness also have other vision problems, including severe myopia, involuntary eye movements, and eyes that do not look in the same direction. These secondary affects are more debilitating than night blindness itself, Dr. Gregg said. RP

Editor’s note: This article is part of a special edition of Retinal Physician that was supported by REGENXBIO.