Regrowing Nerves
Blocking growth inhibitors allows adult neurons to regenerate in mice

Source: “Promoting Axon Regeneration in the Adult CNS by Modulation of the PTEN/mTOR Pathway”
Zhigang He et al.
Science 322: 963-966

Results: Mice with two deleted genes recovered from optic-nerve injury better than normal mice did. Up to 50 percent of their neurons survived two weeks after injury, versus about 20 percent in the control mice. Axons–the long projections in neurons that transmit signals from one cell to another–showed significant regrowth in about 10 percent of the genetically modified animals, but none in the controls.

Why it matters: Nerve cells don’t normally regenerate in adults after injury, so new methods to boost their growth could spur recovery. Other research has demonstrated axon regrowth, but the magnitude of growth in this study makes it significant: some axons grew up to four millimeters in a month. Chemical inhibitors of one of the deleted genes already exist, raising the possibility that the same approach could be applied to humans.

Methods: The researchers deleted two genes, known as Pten and Tsc1, that normally inhibit neural cell growth in the brains of mice. They then crushed the optic nerve. Two weeks after the injury, the scientists tagged the crushed cells with fluorescent markers to assess cell growth and survival.

Next steps: The research group is testing the effect of deleting the same genes in mice with spinal-cord injuries. They are also developing small-molecule compounds that could mimic the deletion of Pten or Tsc1 to boost axon regeneration and functional recovery in patients.