October 25, 2004.
By Gabe Romain,
Credit: Proceedings of the National Academy of Sciences.
Seeing is believing: For the first time, true human retinal stem cells have been isolated, a step towards regenerative treatments for eye diseases
Stem cells from human eyes can generate various cell types required for sight, a finding that marks an important step towards regenerative treatments for eye diseases.
Researcher Derek Van der Kooy from the Department of Medical Biophysics at the University of Toronto in Ontario, Canada and colleagues have found that the human eye contains a small population of retinal stem cells that have the capacity for long-term self-renewal and the ability to make cell types of their tissue of origin.
Although progenitor cells—cells that can only develop into a single cell type—had previously been identified in the retina of humans, stem cells with the capacity for self-renewal had only been found in mice.
"Their facile isolation, integration, and differentiation suggest that human retinal stem cells eventually may be valuable in treating human retinal diseases," write the researchers.
For their study, Van der Kooy and colleagues first cultured eye stem cells taken from humans ranging from newborns to senior citizens. When cultured in test tubes, the stem cells divided and took on the identity of all retinal cell types.
To test the potential of the stem cells in a living organism, the researchers transplanted them into the eyes of mouse pups. Four weeks after transplantation, most of the human stem cells had appropriately migrated, differentiated and integrated at the right developmental times.
The majority of the stem cells took up residence in the photoreceptor layer of the retina. Photoreceptors are the light-sensitive proteins involved in the function of photoreceptor cells, which convert light into signals that can be transmitted to the brain for visual processing.
We transplanted the cells early in the animals' development when all the nutrients and signals they needed for differentiation were still there," says study lead author Brenda Coles of the University of Toronto. "When their eyes fully developed, the human cells survived, migrated into the sensory part of the eye and formed the correct cells."
Cure for blindness?
The researchers' findings could lead to a cure for some types of blindness such as retinitis pigmentosa—a heritable disease of the retina characterized by night blindness and a gradual loss of peripheral vision, caused primarily by the degeneration of the photoreceptors of the retina.
The findings also have implications for treating macular degeneration, a disease affecting central, sharp vision through damage to the macula, which is part of the retina.
This is a long way off, however, says Coles. For one thing, the researchers still need to determine whether retinal stem cells from healthy mice continue developing into photoreceptor cells when transplanted into mice with eye diseases.
"We're starting with mice to see if they can overcome the genetics involved in disease," says Coles. "The eye itself is telling the stem cells what to do, so when we go to a disease model, it is important to know what those signals from the eye are so we can inhibit them or protect the cells."
The research is reported in the Proceedings of the National Academy of Sciences (read abstract).
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