Studies are taking place around the world on the use of stem cells to treat many conditions and diseases. In particular, they are being studied as a treatment for restoring vision. Stem cells have the potential to protect the optic nerve from damage and slow vision loss, as well as possibly replace ocular tissue that has decayed due to diseases like glaucoma.
While stem cells have shown promise in many research projects, they aren’t perfect. There’s the potential of immune rejection, not to mention unwanted cell growth. This realization has led researchers toward the subject of this post. Instead of using cells to restore the retina, maybe cell secretions (called exosomes) can be used instead.
The exosomes are small packages that form inside of cells before they are expelled. Recently scientists have found that the exosomes have proteins and lipid and gene-regulating RNA. The exosomes of one cell can be taken up by another cell by fusing the target cell’s membranes.
Research done at the National Eye Institute (NEI) investigated the use of exosomes on retinal ganglion cells. Mensenchymal stem cells (MSC) derived from bone marrow have been shown to protect retinal cells in traumatic and degenerative eye disease models. Is it possible that the exosomes are responsible for the protective effects of MSC.
Ben Mead, Ph.D., a post-doctoral fellow at NEI, studied the effects of exosomes isolated from bone marrow stem cells on the retinal ganglion cells of rats. The exosomes were injected weekly into the rat’s vitreous and they were tagged with fluorescent markers in order to track their progress. The exosome treated rats lost only a third of their retinal ganglion cells and they maintained visual function. The untreated rats lost 90 percent of their retinal ganglion cells.
This is very promising since loss of retinal ganglion cells is the leading cause of irreversible blindness. “Currently no treatment exists that directly protects retinal ganglion cells from death and following their loss, the retinal ganglion cells cannot be replaced,” Mead said.
What makes the use of exosomes so successful? First of all, they can be purified, stored and dosed in ways that stem cells can’t. In other words, they can be stored as a pharmaceutical might be. When an exosome merges with a target cell the contents of the exosome may spur the cell to make new proteins. In particular, researchers found that the protective effects of the exosomes are mediated by RNA, specifically microRNA. The next step is to find out which microRNA are being delivered into the retinal cells and which proteins are being targeted.
So far it looks that the best way to use the exosomes is to combine them with additional therapies. Also, success of the treatment depends heavily on how often the exosomes have to be administered in order to get the best therapeutic effect. More research is needed before this promising treatment is ready for the general public.