Evidence indicates that the true stem cells in the mammalian brain are the ependymal cells that line the ventricles in the brain and spinal cord, rather than cells in the subventricular zone as biologists previously believed. Brain ventricles are hollow chambers filled with fluid that supports brain tissue, and a layer of ependymal cells lines these ventricles. This finding at UC Irvine supports the finding of MIT researchers posted here a few days ago.
UC Irvine scientists have shown that with proper stimulation they can produce new brain cells to replace those lost to disease or injury. Ependymal cells line the fluid-filled ventricles, so a drug to activate the cells could theoretically travel through this fluid directly to the stem cells.
“One interpretation of previous studies is there are scattered stem cells in the ependymal layer, and it is hard to locate them,” said Peter Bryant, developmental and cell biology professor. “But we believe that all of the ependymal cells are stem cells, and that they all have the ability to be activated.”
Knowing that these normally dormant cells can be coaxed into dividing lays the groundwork for future therapies in which a patient’s own stem cells produce new brain cells to treat neurological disorders and injuries such as Parkinson’s disease, stroke or traumatic brain injury.
“With such a therapy, we would know which cells in the body to target for activation, and their offspring would have all the properties necessary to replace damaged or missing cells,” said Darius Gleason, lead author of the study and a graduate student in the Department of Developmental and Cell Biology. “It is a very promising approach to stem cell therapy."
Gleason and Bryant used rats treated to develop the animal equivalent of Parkinson’s disease. The UCI researchers sought to determine the true location of stem cells in the rats by looking for polarized cells, which have different sets of proteins on opposite sides so that when one divides it can produce two different products. Polarization gives rise to asymmetric cell division, which is the defining characteristic of a stem cell.
They found that polarization exists on the ependymal cells. “It couldn’t have been a stronger signal or clearer message," Gleason said. "We could see that the only cells undergoing asymmetric cell division were the ependymal cells.”
Next, they gave a drug to induce cell division in the rats and examined their brains at intervals ranging from one to 28 days after the treatment. At each interval, they counted cells that were dividing in the ependymal layer. They found the most division at 28 days, when about one-quarter of the ependymal cells were dividing. Previous studies by researchers at other institutions were successful in getting only a few cells to divide in that layer.
Researchers don’t know yet what sparks cell division at the molecular level, but learning that process and how to control it could lead to a safe, effective stem cell therapy.
Adapted from the UC Irvine announcement.