The Study of astrocyte development and function using rat embryonic spinal cord derived glial restricted precursors

Thesis (Ph. D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Pharmacology and Physiology, 2008.The purpose of this thesis is to study the regulation of astrocyte differentiation and to study the function of astrocytes and their interaction with neurons. We isolated glial restricted precursors (GRP) from the rat embryonic neural tube and used this cell type to examine factors that influence the differentiation of astrocytes from GRPs. We demonstrated that endothelin3-mediated signaling was one modulator of astrocyte generation. Endothelin3 induced the generation of an astrocyte precursor cell but not of mature astrocytes from GRP cells. Additionally, endothelin3 blocked the generation of oligodendrocytes, the other potential cell fate of GRP cells. The suppression of the oligodendrocyte lineage pathway by endothelin3 was accompanied by the down-regulation of oligodendrocyte lineage transcription factors. One of these transcription factors, Olig2 was actively degraded by endothelin3 through a post-translational pathway. Olig2 was found to block astrocyte precursor induction when over-expressed in GRP cells. In addition to the effects of endothelin exposure, the intracellular redox state also affected astrocyte generation from GRP cells. More oxidized GRP cells differentiated into astrocytes more readily than reduced GRPs. Moreover, GRP cells dissected from different regions of the rat embryonic neural tube bad different redox states and demonstrated a varied potential to give rise to astrocytes. We also studied the properties of two populations of astrocytes derived from the same GRP cells in terms of the interactions of astrocytes with neurons. These two groups of astrocytes differed in the expression of Olig2, production of axon growth inhibitors, and the ability to support neuronal growth. Olig2 was also a critical regulator of astrocytic phenotype, since over-expression or knock-down of Olig2 changed the properties of either kind of astrocyte. Our work provides new insights into the early stages of astrocyte development and mechanisms underlying roles of astrocytes in injuries, which will enhance the ability to use astrocytes and their precursors in cell transplantation therapies for tissue repair