Scientists reveal retinal cell mapping could promote accurate therapies for blindness

Researchers have identified discrete differences between the cells that make up retinal tissue and the findings can help in developing targeted therapies to treat various diseases that affect the eye’s retina.

The findings of the research were published in the journal ‘Proceedings of the National Academy of Sciences’ by a team of researchers at the National Eye Institute.

Scientists from the National Eye Institute (NEI) discovered five subpopulations of retinal pigment epithelium (RPE)--a layer of tissue that nourishes and supports the retina’s light-sensing photoreceptors.

Using artificial intelligence, the researchers analysed images of RPE at single-cell resolution to create a reference map that locates each subpopulation within the eye. A report on the research was published in Proceedings of the National Academy of Sciences.

“These results provide a first-of-its-kind framework for understanding different RPE cell subpopulations and their vulnerability to retinal diseases, and for developing targeted therapies to treat them,” said Michael F. Chiang, M.D., director of the NEI, part of the National Institutes of Health.

“The findings will help us develop more precise cell and gene therapies for specific degenerative eye diseases,” said the study’s lead investigator, Kapil Bharti, PhD, who directs the NEI Ocular and Stem Cell Translational Research Section.

Vision begins when light hits the rod and cone photoreceptors that line the retina in the back of the eye. Once activated, photoreceptors send signals through a complex network of other retinal neurons that converge at the optic nerve before travelling to various centers in the brain. The RPE sits beneath the photoreceptors as a monolayer, one cell deep.

Age and disease can cause metabolic changes in RPE cells that can lead to photoreceptor degeneration. The impact on the vision from these RPE changes varies dramatically by severity and where the RPE cells reside within the retina.

For example, late-onset retinal degeneration (L-ORD) affects mostly the peripheral retina and, therefore, peripheral vision. Age-related macular degeneration (AMD), a leading cause of vision loss, primarily affects RPE cells in the macula, which is crucial for central vision.

Bharti and colleagues sought to determine if there are different RPE subpopulations that might explain the wide spectrum of retinal disease phenotypes.

The team used artificial intelligence (AI) to analyse RPE cell morphometry, the external shape and dimensions of each cell. They trained a computer using fluorescently labelled images of RPE to analyse the entire human RPE monolayer from nine cadaver donors with no history of significant eye disease.

Morphometry features were calculated for each RPE cell - on average, about 2.8 million cells per donor; 47.6 million cells were analysed in total. The algorithm assessed each cell’s area, aspect ratio (width to height), hexagonality, and number of neighbours.

Previous studies had suggested that RPE function is tied to the tightness of cellular junctions; the more crowded, the better for indicating cellular health.

Based on morphometry, they identified five distinct RPE cell subpopulations, referred to as P1-P5, organized in concentric circles around the fovea, which is the centre of the macula and the most light-sensitive region of the retina.

Compared to RPE in the periphery, foveal RPE tend to be perfectly hexagonal and more compactly situated, with higher numbers of neighbouring cells.

Age-related morphometric changes also may appear in some RPE subpopulations before they’re detectable in others. These findings will help inform future studies using noninvasive imaging technologies, such as adaptive optics, which resolve retinal cells in unprecedented detail and could potentially be used to predict changes in RPE health in living patients.