A new technique is being pioneered by researchers at Penn State University to regenerate functional neurons after brain injury and in those affected by Alzheimer's disease.
The scientists have used the brain's supporting cells, known as glial cells, to grow healthy neurons which are essential for transmitting brain signals.
When the brain is damaged, normal neurons often die or degenerate. Reactive glial cells proliferate as a defence mechanism against bacteria and toxins – but this leads to the formation of glial scars, which prevent the growth of healthy neurons.
Led by Gong Chen, a professor of biology at Penn State University, the team set about trying to transform glial cells back into normal brain cells.
The researchers studied how reactive glial cells respond to a protein known as NeuroD1, which plays an important role in the formation of nerve cells in the part of the brain known as the hippocampus. They reasoned that expressing the protein into reactive glial cells at a site of injury may help to generate new neurons.
A retrovirus which affects glial cells but not other neurons was used to introduce the genetic code for the NeuroD1 protein. The retrovirus was unable to replicate and thus could not destroy the host cells.
NeuroD1 retrovirus was introduced into the brains of mice. It was discovered that two types of reactive glial cells were reprogrammed into normal neurons within a week of being infected with the retrovirus.
In a second study on a mouse model with Alzheimer's disease, it was found that glial cells could be converted into functional neurons – even after the mice had reached 14 months, which is the equivalent of a 60-year-old human being.
The team tested the method on human cells in culture and found that they also regenerated and were able to transmit impulses.
"Our passionate motivation for this research is the idea that an Alzheimer's patient, who for a long time was not able to remember things, could start to have new memories after regenerating new neurons as a result of our in vivo conversion method, and that a stroke victim who could not even move his legs might start to walk again," Professor Chen explained.