Week in Review: Number 4

Fatty Acid Supplements for Improved Retinal Function
Paul S. Bernstein, MD, PhD, and his colleagues at the University of Utah's Chemistry Department recently invented a method to synthesize large quantities of very-long-chain polyunsaturated fatty acids (VLC-PUFAs), a necessary component in proper retinal function. This research is a step toward investigating whether or not giving these lipids as supplements to patients could improve eye diseases such as age-related macular degeneration, diabetic retinopathy, and some inherited retinal diseases. VLC-PUFAs are normally synthesized in the body as a product of the ELOVL4 enzyme, the malfunctioning of which shortens the fatty acid chain and causes autosomal dominant inherited retinal diseases such as Stargardt macular dystrophy. ELOVL4 dysfunction is autosomal dominant in the sense that the mutant proteins lack the appropriate tags, do not go to the proper places in the cell, and overall disrupt proper protein and cellular function where they do end up. But what's interesting about the present study is that is doesn't take a genetics approach, other than using mouse models with defects in the ELOVL4 gene. Rather, Bernstein's lab focuses on nutritional interventions against eye disease. In mouse models thus far, the researchers found that VLC-PUFA supplementation increased levels of the lipids in the retina and improved visual function in both normal mice and mice with the ELOVL4 defect. Indeed, being able to synthesize the lipids in the form of a supplement would open up a new line of orally administered therapeutics for retinal diseases due to dysfunction of very-long-chain polyunsaturated fatty acids.

Generation of Conjunctivae in a Dish
“Many eye diseases affect the parts of the eye that are directly involved in the process of seeing, such as the lens, the retina and the optic nerve,” says corresponding author of the study Ryuhei Hayashi. “In this study, we focused on the tissue lining up the outside of the eye and that is equally important for proper eyesight.” This statement serves to give perspective to the present study. In eye care, one often thinks first of the tissues of the eye proper, tissues that directly contribute to the function of sight. However, equally important are peripheral structures and tissues that support visual function. The tear film is a crucial component to visual clarity, without which the optics of the cornea would be compromised. Dysfunction of the tear film has many etiologies, collectively called dry eye syndrome or ocular surface disease, and is ubiquitous in both normal states and as secondary to pathological or pharmaceutical causes. The goblet cells of the conjunctiva, a translucent tissue that lines the surface of the sclera (the "white part" of the eye) and the inner side of the eyelids, are responsible for secreting the mucin component of the tear film, which keeps the tear film apposed to the eye. The researchers from Osaka University in Japan took a basic science approach to explore generating conjunctival tissue in vitro using human induced pluripotent stem cells (hiPSCs). Their model successfully produced sufficient amounts of goblet cells, opening the possibility of studying conjunctival biology and disease in vitro. Generating conjunctivae in a dish at the surface seems like a trivial project, but given the high prevalence of dry eye syndrome, study of this tissue has the potential for wide-ranging impact. Furthermore, such studies further a model for drug screening and regenerative therapy, a more compassionate preliminary model than those currently used.

Human RPE Cells Transplanted into Monkey Eyes
The possibility of using stem cells to restore vision in degenerative retinal diseases is being explored by an international team of researchers from Singapore, the United States, and Germany. The retinal pigment epithelium (RPE) is the outermost layer of the retina and serves an important function as both a barrier between the retina and the choroid (blood-retina barrier) and in recycling photoreceptor discs, a necessary process at the cellular level for vision to take place. Malfunctioning of the RPE leads to diseases such as macular degeneration. Transplants in the past using the patient's own RPE have had limited success, notably uncertain cell survival delivered by suspension and the risk of uncontrolled cell proliferation. The present study explores the potential of using RPE transplants from donor sources to investigate compatibility matching, as well as the safety and feasibility of this option. The particular type of cell they used, human RPE stem cell-derived RPE (hRPESC-RPE), is itself an interesting approach. But for simplicity, the researchers extracted human RPE stem cells from donated cadaver adult eyes and transplanted them into a non-human primate model (nine cynomolgus monkeys). They found that the stem cell patches remained stable and integrated in vivo for at least three months without serious side effects, and that these stem cell-derived RPE at least partially took over the function of the original RPE to support the endogenous photoreceptors. The complexity of restoring functional vision extends far beyond safe cell survivability, but what is attractive about this method is that it, if successful in clinical trials, would open the possibility of an unlimited source of retinal donor tissue for transplant.

Retinal Organoids for the Study of Rare LCA
Researchers at the National Eye Institute recently investigated gene augmentation in a rare autosomal dominant form of Leber congential amaurosis (LCA) through retinal organoid models made from patient cells. Leber congenital amaurosis is a rare inherited retinal disease caused by a number of different faulty genes, resulting in improper function of the opsin proteins in the eye's photoreceptors. Opsins are necessary for the detection of light. Leber congenital amaurosis gained public attention in 2017 when the FDA approved Luxturna (voretigene neparvovec) for the treatment of one form of LCA due to a mutation in the gene RPE65. As a gene therapy, Luxturna very specifically treats one particular form of LCA and is ineffective for other forms caused by other faulty genes, such as the form addressed in the present study. Of particular note is the fact that the form of LCA under study at the NEI, caused by mutations in the CRX gene, is autosomal dominant. Autosomal dominant diseases present additional challenge to gene therapy in the sense that the mutated protein often interferes with the proper functioning of the normal protein, so increasing the normal protein could exacerbate the disease in unpredictable ways. To explore the effect of gene augmentation, the NEI scientists created retinal organoid models from two patients with CRX-related LCA as well as from their unaffected family members. The details of the engineering steps can be found in the NEI article. But the result of this proof-of-concept study is that gene augmentation restored some CRX protein expression (opsins) in the retinal organoids from the two affected patients. Autosomal dominant LCA is an extremely rare eye disease, but it provides the opportunity for development of gene therapy techniques for a variety of inherited diseases.

Cerebral Visual Impairment in Some U.K. Children
Vision is a product of both properly functioning eyes and properly functioning brains. Researchers at the University of Bristol in the U.K. seek to call attention to the possibility that many young children experience undiagnosed brain-related visual impairment. Their study is relatively small, comprising 2,298 children aged 5 to 11 years across 12 schools, and is largely subjective, using teacher and parent questionnaires. Of these school children, the researchers invited only 262 for a detailed assessment and further testing to identify children with brain-related visual problems suggestive of cerebral visual impairment (CVI). The difficulties include problems with eye movements, visual field, recognition of objects and seeing things in clutter. They also found links between visual difficulty and difficulty in school performance and suggest, "If interventions can work to reduce the impact of these problems on children’s learning, it might improve both educational and well-being outcomes for children." Studies in other countries provide an interesting perspective into differences in scope of practice among health professions depending on where they practice. This study was conducted by doctors in the Paediatric Ophthalmology department at Bristol Medical School, however, in the U.S., the scope of this topic would fall under optometry.

In Everyday News
(1) Reading outside improves eyesight
(2) Stem cells show potential in treating AMD
(3) An increase in styes from mask wearing?