Researchers here are working on a way to remove a type of scarring that occurs in brain injuries and forms of neurodegeneration:
When the brain is harmed by injury or disease, neurons often die or degenerate, but glial cells become more branched and numerous. These "reactive glial cells" initially build a defense system to prevent bacteria and toxins from invading healthy tissues, but this process eventually forms glial scars that limit the growth of healthy neurons. "There are more reactive glial cells and fewer functional neurons in the injury site, so we hypothesized that we might be able to convert glial cells in the scar into functional neurons at the site of injury in the brain."
[The researchers] began by studying how reactive glial cells respond to a specific protein, NeuroD1, which is known to be important in the formation of nerve cells in the hippocampus area of adult brains. They hypothesized that expressing NeuroD1 protein into the reactive glial cells at the injury site might help to generate new neurons - just as it does in the hippocampus. To test this hypothesis, his team infected reactive glial cells with a retrovirus that specifies the genetic code for the NeuroD1 protein.
In a first test, [researchers injected] NeuroD1 retrovirus into the cortex area of adult mice. The scientists found that two types of reactive glial cells - star-shaped astroglial cells and NG2 glial cells - were reprogrammed into neurons within one week after being infected with the NeuroD1 retrovirus.
In a second test, [researchers] used a transgenic-mouse model for Alzheimer's disease, and demonstrated that reactive glial cells in the mouse's diseased brain also can be converted into functional neurons. Furthermore, the team demonstrated that even in 14-month-old mice with Alzheimer's disease - an age roughly equivalent to 60 years old for humans - injection of the NeuroD1 retrovirus into a mouse cortex can still induce a large number of newborn neurons reprogrammed from reactive glial cells.