The pathway--which acts through a novel and unexpected mechanism--inhibits production of astrocytes during the early stages of brain development, thereby favoring the production of neurons. (Astrocytes provide structural and functional support to neurons, but can also regulate their differentiation.) Children's neurobiologist Gabriel Corfas, PhD, senior investigator on the study, says the discovery could have implications for diseases such as Alzheimer's disease, schizophrenia and autism.
One key component of the pathway is a protein called erbB4 that straddles the outer membrane of the neural stem cell. Corfas's team showed that mice lacking erbB4 produced astrocytes earlier in embryonic development than normal. ErbB4 is activated by another protein called neuregulin 1 (NRG1), and then is cut in two by a third critical protein called presenilin, the researchers showed. The half of erbB4 that resides inside the cell--a protein called E4ICD--then joins with other proteins in the cell and travels to the cell nucleus. "Once in the nucleus, E4ICD represses genes that trigger astrocyte production, and thereby inhibits astrocyte formation," explains S. Pablo Sardi, PhD, a postdoctoral fellow at Children's and the study's first author.
Previous studies have found presenilin activity to be altered in Alzheimer's disease, and that erbB4 is abundant around the plaques found in Alzheimer's patients' brains. Taken together, the evidence suggests that presenilin's role in Alzheimer's may have
Source:Children's Hospital Boston