Scientists from University College London have made an important step towards understanding nerve re-growth process. The finding published in the latest issue of Cell sheds light on the mechanisms underlying peripheral nerves regeneration after injury.
In contrast to the spinal cord nervous cells, the peripheral nerves connecting central nervous system to organs and limbs are known as being able to re-grow after the injury. Peripheral nerve cells consist of nucleus placed in the spinal cord and the axons 'running' all the way to different organs or throughout the entire limb. When axons get damaged, their cut parts that lost the connection to the nucleus degenerate. To let the axon re-grow, two separated parts need to be reconnected again through the injured tissue. The organism involves sophisticated mechanisms in order to fulfill this task. As it was known earlier, Schwann cells act to help axons regenerate. Schwann cells wrap axons and in their normal state are rather inactive. However, once the neuron is damaged, they re-differentiate and gain the properties of stem cells. After that, they regroup and serve as a bridge between disconnected nerve parts in the wound. Liver cells and endothelial cells lining blood vessels are other cell types known for their ability to re-differentiate back to a stem-cell-like state.
However, as shown in the new study, Schwann cells themselves are not enough to regenerate the nerves properly. In that function they are assisted by fibroblasts which are known as being irreplaceable in wound healing, but which role in axon re-growth has only now come to light.
In response to a signal sent by fibroblasts—so-called ephrin-B signal—Schwann cells leave nerve stump and regroup into cords across the injured part. Axon re-growth takes place along these cords. Without the signal, Schwann cells are not capable of an organized migration, which results in improper axon regeneration. The response to the signal depends on the so-called Sox2 factor. This factor plays major role in embryonic stem cell development as well as serves for adult cells reprogramming into the state of stem cells.
The scientists head for developing methods that could improve the natural axon regeneration, as the natural mechanism of the peripheral nerve re-growth is imperfect. For example, if a limb was sewn back after being cut off, some movements may return but its functioning will be impaired.