Stem cell secretions may protect against glaucoma

Stem cell secretions, called exosomes, appear to protect retinal cells in rats, offering a potential therapy for degenerative eye diseases like glaucoma. 

Researchers say that exosome treatment could avoid the potential risks of using whole stem cells, such as the rejection by the immune system or the development of tumours.

Researchers at the US National Eye Institute (NEI) investigated the effect of exosomes on retinal ganglion cells using rats that had their optic nerve damaged to mimic glaucoma. They injected the rats on a weekly basis with exosomes from bone marrow mesenchymal stem cells, using fluorescent labels to monitor their delivery into the retinal cells.  

The researchers found that exosome-treated rats lost a third of their retinal ganglion cells, compared with a 90 percent loss among untreated rats after optic injury. When the researchers measured the retinal ganglion cells' electrical function, they observed that the exosome-treated cells continued to behave normally. 

Exosomes are membrane-enclosed packages, containing proteins, lipids and micro RNA. Neighbouring cells can take up secreted exosomes, prompting changes in signalling pathways and protein production. 

Exosome therapy avoids the potential risks of using whole stem cells, such as the body rejecting the cells as 'foreign' or uncontrollable cell growth leading to tumours. 'Exosomes can be purified, stored and precisely dosed in ways that stem cells cannot,' explained Dr Ben Mead of the NEI, who led the study, which was published in the journal Stem Cells Translational Medicine. 

The authors say that it opens the possibility of 'cell-free therapy for traumatic and degenerative ocular disease'. They suggest that the protective effects of exosomes are caused by the transfer of microRNA contained in the exosomes, but more research is needed to understand their contents and how they work. 

'We need to know which particular microRNA – there are more than 2000 different microRNA molecules – are delivered into the retinal ganglion cells and what proteins or signalling pathways are being targeted upon arrival,' said Dr Stanislav Tomarev, a principal investigator at NEI and the study's co-author. 'We also need to attempt to target exosomes to specific sets of neurons and other cell types or groups of cells.'

Glaucoma is caused by a blockage of the drainage tubes in the eye. The resulting increase in pressure damages the optic nerve and can eventually lead to blindness. The associated vision loss is currently incurable, but early treatment can delay disease progression. 

Dr Tomarev added that the exosome approach needs to be optimised and may work best in combination with other therapies.