Optic Nerve Regeneration

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Optic Nerve Regeneration

• By Jessica Anderson

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The Optic Nerve

• The optic nerve is the nerve that transmits
  visual information from the retina to the brain.

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Damage To The Optic Nerve

• Damage to the optic nerve typically causes
  permanent and potentially severe loss of vision,
  and the type of visual field loss will depend on
  which portions of the optic nerve were damaged.
  Injury to the optic nerve or an illness can
  cause damage to the optic nerve, some examples
  Leber's Hereditary Optic Neuropathy glaucoma,
  trauma, toxicity, inflammation, ischemia,
  infection (very rarely), or compression from
  tumors or aneurysms.

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Healthy Optic Nerve Damaged Optic
Nerve
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Regeneration Discovery

• Researchers at Childrens Hospital Boston
  discovered a naturally occurring growth factor
  called oncomodulin that stimulates regeneration
  of injured nerve fibers (axons) in the central
  nervous system. Under normal conditions, most
  axons in the mature central nervous system (which
  consists of the brain, spinal cord and eye)
  cannot re-grow after injury. Neuroscientists
  Yuqin Yin, MD, PhD, and Larry Benowitz, PhD, who
  are also on the faculty of Harvard Medical
  School, did their studies in the optic nerve.

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How was Oncomodulin discovered?

• Studying the optic nerve, researchers found that
  an injury to the eye activated axon growth it
  caused an inflammatory reaction that stimulated
  immune cells known as macrophages to move into
  the eye. It was discovered that the macrophages
  secreted an essential protein. Further studies
  revealed it to be oncomodulin, a little-known
  molecule first observed in association with
  cancer cells. For oncomodulin to work, it must be
  given along with an agent that raises cell levels
  of cyclic AMP, a messenger" that initiates
  various cellular reactions. Increased cyclic AMP
  levels are needed to make the oncomodulin
  receptor available on the cell surface.

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• When oncomodulin was added to retinal nerve cells
  in the lab, with known growth-promoting factors
  already present, the growth of axons -- or cells
  in the optic nerves -- nearly doubled.
• No other growth factor was as potent, the
  researchers said.

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Experiment On Rats

• In live rats with optic-nerve injury, oncomodulin
  released from tiny sustained-release capsules
  increased nerve regeneration five- to seven-fold
  when given along with a drug that helps cells
  respond to oncomodulin.

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• Here you can see a dramatically increased growth
  of axons into the optic nerve (bottom panel) as
  compared with controls who received empty
  capsules (top panel). The asterisk indicates the
  injury site.

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• Benowitz, the studys senior investigator,
  believes oncomodulin could someday prove useful
  in reversing optic-nerve damage, and in addition,
  the lab has shown that oncomodulin works on at
  least one other type of nerve cell, and now plans
  to test whether it also works on the types of
  brain cells that would be relevant to treating
  conditions like stroke and spinal cord injury.

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Limitations

• It remains to be seen whether nerve fibers that
  regenerate after treatment with oncomodulin would
  restore lost sight in laboratory animals.
  Experiments were conducted to identify
  oncomodulin and to explore how well it helps
  damaged nerves regenerate. In order for the
  nerves to be functional, the nerve fibers would
  not only have to grow long enough to re-connect
  the eye and the brain, they'd also have to
  connect to the proper locations in the brain that
  process visual signals.
• A further limitation is treatment would not
  replace any nerve cells that had died due to
  injury.

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References

• http//www.medicalnewstoday.com/articles/6235.php
• http//www.sciencedaily.com/releases/2006/05/06051
  5000109.htm
• http//www.news.harvard.edu/gazette/2006/05.18/13-
  eyenerve.html
• http//health.dailynewscentral.com/content/view/00
  02251/51/
• http//en.wikipedia.org/wiki/Optic_nerve