Scientists from the National Eye Institute have shown that stem cell secretions called exosomes promote survival of retinal ganglion cells in rats, suggesting potential new therapies for glaucoma.
Exosomes offer some key advantages over transplanting whole stem cells, which carry the risk of immune rejection and unwanted cell growth.
“Exosomes can be purified, stored and precisely dosed in ways that stem cells cannot,” said Ben Mead, PhD, a post-doctoral fellow at NEI and lead researcher for the study, published on January 26 in Stem Cells Translational Medicine.
Using a rat glaucoma model, Mead studied the effect of weekly intravitreal injections of exosomes on retinal ganglion cells. The extracellular vesicles, which were tracked using fluorescence, successfully delivered their cargo to the inner retina, including the retinal ganglion cells.
Treated rats lost about a third of their retinal ganglion cells following optic nerve injury, compared with a 90% loss among untreated rats. Stem cell exosome-treated retinal ganglion cells also maintained function, which was measured using electroretinography.
The research team further determined that the protective effects were mediated by microRNA, but more research is needed to understand the specific contents of the exosomes.
“We need to know which particular microRNA – there are more than 2,000 different microRNA molecules – are delivered into the retinal ganglion cells and what proteins or signaling pathways are being targeted upon arrival,” said Stanislav Tomarev, PhD, a principal investigator at NEI and the study’s coauthor. “We also need to attempt to target exosomes to specific sets of neurons and other cell types or groups of cells.”
The optimal exosome approach also requires elucidation, including exploring combining exosomes with additional therapies. From a treatment feasibility standpoint, much will depend on how frequently exosomes need to be administered to achieve a therapeutic effect, Tomarev said.