Researchers have created a miniature human retina in a dish using human induced pluripotent stem cells (iPS), which they say notably includes functioning photoreceptor cells capable of responding to light, the first step in the process of converting it into visual images.
Reported in the journal Nature Communications, the achievement could eventually enable genetically engineered retinal cell transplants that halt or even reverse a patient’s march toward blindness, the researchers say.
“We knew that a 3D cellular structure was necessary if we wanted to reproduce functional characteristics of the retina, but when we began this work, we didn’t think stem cells would be able to build up a retina almost on their own. In our system, somehow the cells knew what to do,” said study leader Valeria Canto-Soler, who is Assistant Professor of Ophthalmology, at the Johns Hopkins University School of Medicine.
When the retinal tissue was at a stage equivalent to 28 weeks of development in the womb, with fairly mature photoreceptors, the researchers tested the mini-retinas to see if the photoreceptors could sense and transform light into visual signals.
They did so by placing an electrode into a single photoreceptor cell and then giving a pulse of light to the cell, which reacted in a biochemical pattern similar to the behavior of photoreceptors in people exposed to light. Assist. Prof. Canto-Soler said the lab-grown photoreceptors responded to light the way retinal rods do. Human retinas contain two major photoreceptor cell types called rods and cones. The vast majority of photoreceptors in humans are rods, which enable vision in low light. The retinas grown by the Johns Hopkins team were also dominated by rods, she said.
Assist. Prof. Canto-Soler said the newly developed system gives researches the ability to generate hundreds of mini-retinas at a time directly from a person affected by a particular retinal disease such as retinitis pigmentosa. This provides a unique biological system to study the cause of retinal diseases directly in human tissue, instead of relying on animal models.
The system, she said, also opens an array of possibilities for personalised medicine such as testing drugs to treat these diseases in a patient-specific way. In the long term, the potential is also there to replace diseased or dead retinal tissue with lab-grown material to restore vision, she said.
Assist. Prof. Canto-Soler cautioned that photoreceptors are only part of the story in the complex eye-brain process of vision, and her lab hadn’t yet recreated all of the functions of the human eye and its links to the visual cortex of the brain.