Better treatment for spinal injuries could be on its way

WASHINGTON - Improved treatment for spinal injuries could be on its way, as scientists have found that the rate and direction of axon growth in the spinal cord can be controlled.

USC College’s Samantha Butler and collaborators, found that a series of connections at the cellular level produce a guidance cue that tells an axon how fast and in which direction to grow in an embryonic environment. Butler and her team also discovered that by modulating the activity of enzyme LIM domain kinase 1 (Limk1), the rate of axon growth could be stalled or accelerated.

Future applications of these findings may include enhancing the ability to regenerate neuronal circuits in patients suffering from spinal cord injuries or neurodegenerative diseases.

Under normal conditions, guidance cues cause a developing neuron to extend an axon into the environment. In a developing spinal cord, the cue comes in the form of a repellant, which acts from behind the cell body to direct the growth of the axon in the opposite direction. This repellant is mediated by bone morphogenetic proteins (BMPs).

In the beginning of the multi-step growth process, BMPs bind to a cell and activate its receptors; then a second messenger is triggered, in this case Limk1. Limk1 modifies the activity of a protein called cofilin. When cofilin is active, the axon grows. If the cofilin becomes inactive, growth comes to a halt.

Butler and her team discovered that by increasing the amount of cofilin, or decreasing the amount of the restricting Limk1, the commissural axon growth accelerated. Likewise, when the amount of cofilin was decreased, or the amount of Limk1 was increased, axon growth stopped.

The axon growth in embryonic spinal cords in which Limk1 was lowered appeared to be more advanced than in controls - the axons grew up to 25 percent faster.

Since the axon is growing through an ever-changing environment, if the accelerated rate moves the axon to its subsequent signal destination too fast, that destination may not yet be created.

The study was published online in the Journal of Neuroscience. (ANI)