April 7, 2011
Scientists Use Stem Cells To Grow Retina
In a major breakthrough in the field of regenerative medicine, scientists have for the first time created a part of the eye critical for vision using animal stem cells, according to a study published Wednesday in the journal Nature.
The research could pave the way to new treatments for blindness and human eye diseases, and experts say it may even be possible to one day restore vision with transplanted retinas generated from a patient's own stem cells.
The researchers, led by Yoshiki Sasai of the RIKEN Center for Developmental Biology in Japan, conducted lab experiments using mice. They started with pluripotent stem cells, the universal stem cells for nearly every specialized cell in an organism. Until now, stem cells have mainly been viewed as a potential source of replacement tissue composed of a single type of cell, like muscle cells, for example. The ability to generate a more complex set of cells, or even an entire organ, was thought to require intricate chemical interactions with neighboring tissues during gestation, and therefore impossible in the absence of the natural process of cell division and growth.
However, Sasai and colleagues used new techniques, and were able to set in motion the transformation of mouse embryonic stem cells into an optic cup -- the layered, three-dimensional structures that become the retina in an eye.
Most importantly, the cells did the work themselves, without being pushed into any particular shape.
"What we've been able to do is resolve a nearly century-old problem in embryology by showing that retinal precursors have the inherent ability to give rise to the complex structure of the optic cup," said Sasai in a statement.
Starting as a disorganized mass, the stem cells formed themselves into the two-walled structure that corresponds to the inner and outer layers of the retina during the development of an embryo.
"We are now well on our way to becoming able to generate not only differentiated cell types, but organized tissues" Sasai said.
The breakthrough is particularly applicable for a group of genetic eye conditions known as retinitis pigmentosa, which attacks vision by damaging the retina, leading to blindness, Sasai said. People with retinitis pigmentosa experience a slow, gradual decline in vision because photoreceptor cells degenerate and die.
"As a step forward in the lead-up to cell replacement or even organ therapy, this is a really significant piece of work," said Richard Lang, director of the visual systems group at the Cincinnati Children's Hospital, during an interview with the AFP news agency.
"It shows that relatively simple culture conditions can be used to generate whole organ primordia," he said, referring to the early, embryonic stage of organ development.
Lang said the while the goal of generating human eye tissue remains far off, other scientists are making parallel progress on other types of tissue.
"It feels like it won't be long before the first opportunity for experimental clinical use comes along," he said.
In a commentary about the study, Robin Ali and Jane Snowden of University College London wrote that the new self-generating proto-eye had the signature molecular markers of both the neural retina, which is linked to the brain, and the retinal pigmented epithelium, which helps keep the eye free of debris.
"An even more striking proof that these are genuine retinas is that, in culture, the synthetic optic cups undergo cell differentiation ... into all the main retinal cell types, including photoreceptors," they wrote.
The study was published online April 6 2011 in the journal Nature.
Image Caption: An ES cell-derived optic cup virtually inserted into a test tube. Credit: RIKEN CDB/HO/M. Eiraku And Y.Sasai
On the Net: