Making the optic nerve sprout anew

From Washington, D.C., at a seminar on Research to Prevent Blindness

Damage to the optic nerve sabotages sight. Without this essential conduit to the brain, images gathered by the eye have nowhere to go. Scientists now report that a compound made during inflammation, a natural reaction to injury, can induce optic nerve regeneration in lab dishes.

The optic nerve is composed of long tendrils, called axons, that grow from so-called retinal ganglion cells in the back of the eye. When damaged, these axons normally do not regrow, says Larry I. Benowitz, a neuroscientist at Harvard Medical School and Children’s Hospital in Boston.

Fish and amphibians can regenerate optic nerve tissue, so Benowitz and his colleagues examined goldfish and found two compounds essential to this process. The mammalian equivalents of these molecules are the sugar mannose and a signaling compound called cyclic adenosine monophosphate (cAMP).

Meanwhile, the researchers also looked closely at macrophages, immune cells that often contribute to inflammation after injuries, including optic nerve damage. They found that macrophages produce a protein that orchestrates axon regrowth.

In a lab dish, a cocktail of mannose, cAMP, and the macrophage protein induced extensive axon growth in rat retinal ganglion cells, Benowitz says.

While Benowitz has yet to divulge the identity of the macrophage protein, he did say it is “an obscure protein that has been seen in other contexts but never in relationship to axon growth.”

Next, the researchers plan to place beads loaded with the regeneration cocktail into the eyes of rats with damaged optic nerves to see whether new axons sprout.

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