Biologists at U of T have found a way to grow eye tissue using human stem cells.
Researchers from U of T, Switzerland, and the U.S. transplanted stem cells from adult human eyes into young mouse embryos that had had some of their eye tissue removed. Stem cells are like “blank cells”; they have, to a degree, the ability to grow into almost any kind of tissue. Contrary to popular belief, stem cells are found in both embryos and in adult animals.
When put in the eyes of mice embryos, the human stem cells proliferated and developed properly, forming the different kinds of cells that line the back of the eye and allow us to see: photoreceptor cells, that catch light, and retinal pigment epithelial (RPE) cells, which supply nutrients to the photoreceptors and ensure their proper functioning. The stem cells formed the right kinds of cells in the right places, resulting in healthy eyes indistinguishable from normal mouse eyes.
“The stem cells are making the cell types that we’d desperately like to make for clinical applications,” said Brenda Coles, lead author of the study. Researchers are hoping eventually to use stem cells to treat eye diseases that involve the death or degeneration of photoreceptor cells and RPE cells.
Degenerative eye diseases usually occur later in life, and involve the slow gradual loss of vision, often resulting in total blindness. An estimated 1.5 million people worldwide suffer from degenerative eye diseases.
“Right now there’s very little out there that can truly help people that are progressively going blind,” said Coles.
Coles notes that while it may be ten years before we see any clinical applications from this study, the prospects of growing new eye tissue in humans appear good. “[Eye] stem cells behave the same in mice and in humans, which is great because it means anything we can do in mice for the most part is going to be directly transferable to humans,” said Coles. Stem cells found in the brain, on the other hand, don’t act the same in mice and humans. This might slow the progress of research because any discoveries researchers make in lab animals might not work in humans.
Coles and her colleagues, however, still have more work to do on regenerating eye tissue in mice before they can be confident in the usefulness of their work. This study was performed on healthy mice that would otherwise have still grown normal eyes. The goal now is to treat unhealthy eyes. The stem cells might grow properly if they are put into a diseased eye.
Researchers are also hoping to find a way to use stem cells that come from patients themselves. Not only would this extinguish a lot of ethical concerns, but it would also be a great deal easier on the patients if stem cells from their own eyes could be enticed to grow properly. “We’re trying to go at this from a couple of different angles,” said Coles.
When asked if this treatment could be used to help people who were born blind, her reply was not optimistic: “Probably not.” In addition to having normal eyes, humans also need to have properly formed nerve connections between the eyes and brain. People who were born blind never had these connections form properly as a fetus, so as of now there is not much hope of restoring their sight.