Researchers have identified a novel mechanism by which neural stem cells can help to repair and assist other brain cells:
Stem cells hold great promise as a means of repairing cells in conditions such as multiple sclerosis, stroke or injuries of the spinal cord because they have the ability to develop into almost any cell type. Now, new research shows that stem cell therapy can also work through a mechanism other than cell replacement. A team of researchers [has] shown that stem cells "communicate" with cells by transferring molecules via fluid filled bags called vesicles, helping other cells to modify the damaging immune response around them. "These tiny vesicles in stem cells contain molecules like proteins and nucleic acids that stimulate the target cells and help them to survive - they act like mini "first aid kits". Essentially, they mirror how the stem cells respond to an inflammatory environment like that seen during complex neural injuries and diseases, and they pass this ability on to the target cells. We think this helps injured brain cells to repair themselves."
Mice with damage to brain cells - such as the damage seen in multiple sclerosis - show a remarkable level of recovery when neural stem/precursor cells (NPCs) are injected into their circulatory system. PCs make vesicles when they are in the vicinity of an immune response, and especially in response to a small protein, or cytokine, called Interferon-g which is released by immune cells. A highly specific pathway of gene activation is triggered in NPCs by IFN-g, and that this protein also binds to a receptor on the surface of vesicles. When the vesicles are released by the NPCs, they adhere and are taken up by target cells. Not only does the target cell receive proteins and nucleic acids that can help them self-repair, but it also receives the IFN-g on the surface of the vesicles, which activates genes within the target cells.