In a new study, researchers have shown for the first time that when one optic nerve in the eye is damaged, as in glaucoma, the opposite optic nerve comes to the rescue by sharing its metabolic energy.
In doing so, however, the undamaged optic nerve becomes vulnerable to further metabolic stress, which could explain why the neurodegeneration observed in this and other diseases spreads between brain regions.
The study suggests a potential new approach to treating neurodegenerative diseases like glaucoma and Alzheimer’s disease by beefing up the metabolic resources of the involved neurons.
The research was conducted by a team at Vanderbilt University Medical Center (VUMC).
Glaucoma, a leading cause of blindness, is caused by sensitivity to ocular pressure, which leads to degeneration of the eye’s neural projection to the brain.
Crucial to neuronal health are astrocytes, the star-shaped glial cells that store glycogen and release it as glucose, the fuel that neurons need to function since they do not store their own energy source.
Using positron emission tomography (PET) imaging, which can map the metabolic activity of cells in different tissues, the researchers showed that when one optic nerve was stressed by a rise in intraocular pressure, metabolites including glycogen were transferred from the healthy optic nerve via their crossover point in the brain.
The transfer phenomenon helps explain the bilateral effects seen in neurodegenerative diseases. Alzheimer’s disease, for example, can start in one hemisphere of the brain and travel to the next.
While sharing energy helps the diseased tissue, the tissue that’s donating its energy stores becomes more susceptible to subsequent injury.
This implies that a way to slow neurodegeneration generally would be to boost metabolic resources in the brain.
One way that can be done is by targeting astrocytes to reprogram them to create and store more metabolites to share with neurons.
The team says using gene therapy to reprogram neurons in certain diseases of the visual system has been shown to be effective.
One author of the study is David Calkins, Ph.D., Vice Chair of the Department of Ophthalmology and Visual Sciences at VUMC.
The study is published in PNAS.
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