As we age, vision problems are unavoidable. Age-related macular degeneration breaks down a thin layer of cells in the back of your eye — the retinal pigment epithelium (RPE) — on the way to causing vision loss.
Recently published research from the Neural Stem Cell Institute in Rensselaer, New York, shows the RPE to have some very interesting and unusual characteristics. Researchers discovered that the RPE is able to self-regenerate in vivo and act as stem cells — differentiating into nerve, cartilage, and bone cells when grown in the correct medium.
But that's not the best part of the report - the RPE is available for extraction from the recently deceased, and from living donors, making available a vast supply of stem cells without any ethical entanglements. Let's take a look at the RPE and it's function within the eye along with how a set of researchers stumbled on this set of life giving characteristics.
Top image from Masca_Riden/Deviant Art.
What does the retinal pigment epithelium do?
The retinal pigment epithelium (RPE) is a thin layer of cells that acts as a support system for the retina. You might have seen the RPE before and not noticed it — the RPE is black in color against the rest of a dissected cow eye.
The RPE shields the retina from receiving too much light, and it also supplies glucose for energy and secretes a substance that builds and maintains the retina. Due to regenerative properties observed in the RPE among amphibians and small animals, this thin layer of cells is a hot topic in restorative medical research.
A single RPE cell can regenerate the entire retinal pigment epithelium
The researchers obtained RPE cells by removing the layer present in recently deceased humans. Single RPE cells isolated in the course of the study, often failed to replicate or replicated dimly (2-4 cycles). However, a little over 10% of the cells divided and created a cobblestone monolayer in the culture. Cloning of successful lines enhanced the success in creating a monolayer, with a little over 25% of cloned lines proliferating extensively and better than the parent cells.
These are in vitro experiments, but they open up a variety of possibilities for in vitro and in vivo growth, and possibly replacement or enhancement of an in vivo retinal pigment epithelium.
From the back of the retina to skeletal tissue
The really exciting avenue for RPE cells is the ability to generate different types of tissue. Nerve, bone, fat, and cartilage cells grew from retinal pigment epithelium cells placed in specific growth situations during the course of this study.
The success of advanced differentiation combined with a a ready supply is a boon for stem cell technology, yielding a pliable set of cells without eliciting an ethical outcry. If stem neural stem cells can be harvested from living or recently deceased humans, most ethical stem cell conundrums, regardless of your political or ideological background, are removed from the table.
Still useful after a century of life
Retinal pigment epithelium cells successfully regenerating and differentiating into other cell types after a century of life is a a bizarre and wonderful phenomenon. Emphasizing the importance of this feature, Sally Temple, corresponding author of the Cell: Stem Cell article Adult Human RPE Can Be Activated into a Multipotent Stem Cell that Produces Mesenchymal Derivatives of the Neural Stem Cell, says
"You can get these cells from a 99-year-old,[...] 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.
Not just for cadavers...
Researchers obtained stem cells from donors who died hours before harvest, but it is possible to donate cells from your retinal pigment epithelium prior to casting off this mortal coil.
Stimulating the RPE without harvesting the cells could be particularly interesting, and open up an avenue for regeneration of the retina in living subjects. Sally Temple, Scientific Director of the Neural Stem Cell Institute in Rensselaer, New York, makes retrieving the stem cells from live subjects sound easy:
"You can literally go in and poke a needle in the eye and get these cells from the subretinal space, [...] It sounds awful, but retinal surgeons do it every day."
Grow your own spare parts!
Getting stuck in the eye with a needle is never an appealing mental image, but access to a personal supply of stem cells or "donor" cells from the recently deceased (a situation no different than giving a whole organ like a liver) removes a significant amount of conservative stigma and ethical implications that comes along with obtaining stem cells for research use and medical applications.
Maybe we'll finally tap some of the regenerative abilities we see in other areas of nature (multiple heads on spliced planaria!) for human medical application along the way as well. At the very least, we might save the time, effort, and political entanglements that would come along with future generations growing brain-dead clones for spare body parts.