That cell layer, known as the retinal pigment epithelium (RPE), underlies and supports photoreceptors in the light-sensitive retina. Without it, photoreceptors and vision are lost. The new study shows that the RPE also harbors self-renewing stem cells that can wake up to produce actively growing cultures when placed under the right conditions. They can also be coaxed into forming other cell types.
"You can get these cells from a 99-year-old," said Dr. Sally Temple, co-founder and scientific director of the Neural Stem Cell Institute in Rensselaer, New York. "These cells are laid down in the embryo and can remain dormant for 100 years. Yet you can pull them out and put them in culture and they begin dividing. It is kind of mind boggling."
"You can literally go in and poke a needle in the eye and get these cells from the subretinal space," she says. "It sounds awful, but retinal surgeons do it every day." By comparison, access to most other neural stem cell populations would require major surgery.
Temple said they were curious about the proliferative potential of the RPE given that the tissue is known to be capable of regenerating entire retinas in salamanders. But that plasticity in adulthood had seemed to be lost in mice and chicks. Still, "given the evolutionary evidence, we thought it was worth revisiting," she said.
They placed RPE tissue taken from 22-year-old to 99-year-old cadavers into many culture conditions to see what they could make the cells do. They found one set of conditions that got the cells dividing. Not all of the RPE cells have this regenerative potential, but perhaps 10 percent of them do.
Further work showed that the cells are multipotent, which means that they can form different cell types, though the researchers admit there is more to do to fully explore the cells' differentiation capacity.
There are other implications as well. For example, these cells may explain diseases in which other tissue types show up in the eye. Their presence also suggests that there might be some way to stimulate controlled repair of the eye in the millions of people who suffer from age-related macular degeneration.
"I think it might be possible," Temple said.
Note: One of our Stem Cell Sector companies, Advanced Cell Technology (ACTC.OB), has initiated two Phase 1 clinical trials to test the safety of their human embryonic stem cell-derived RPE cellular therapy for Stargardt's Macular Dystrophy (SMD) and for Dry Age-Related Macular Degeneration (Dry AMD). Both the FDA and the European Medicines Agency (EMA) have also granted ACT's RPE cells "Orphan" status for treatment of Stargardt's Disease. ACTC recently secured a patent on its “embryo-safe” single-blastomere technology and in June of 2010 secured a broad patent for production of RPE cells.
Adapted from the Neural Stem Cell Institute in Rensselaer, New York announcement.
Comments