When they compared the chemical makeup of the areas known to generate new neurons in the hippocampus with other parts of the brain, the team discovered that astrocytes in the hippocampus were sending one signal to the stem cells and that those from the rest of the brain were sending a different signal to stem cells.
In the second (PNAS) study, the team went on to discover the exact nature of those different chemical signals. They learned that in the areas where stem cells were sleeping, atrocytes were producing high levels of two related molecules--ephrin-A2 and ephrin-A3. They also found that removing these molecules (with a genetic tool) activated the sleeping stem cells.
The team also found that astrocytes in the hippocampus produce not only much lower levels of ephrin-A2 and ephrin-3, but also release a protein named sonic hodghoc that, when added in culture or injected into the brain, stimulates neural stem cells to divide and become new neurons.
"These findings identify a key pathway that controls neural stem cell growth in the adult brain and suggest that it may be possible to reactivate the dormant regenerative potential by adding sonic hedgehoc, or blocking ephrin-A2 or ephrin-A3," says Dr. Jianwei Jiao, the first author of the two papers,
The next step for the team will be to stimulate the sleeping stem cells in animals who are models of neurodegenerative disorders, such as Parkinson's disease, to see if the brains can repair themselves and restore their damaged functions.
|Contact: Patti Jacobs|
Schepens Eye Research Institute