Gliogenesis and Glial Function After Perinatal Brain Injury Open Access
Understanding the response of glia to different brain pathologies is important in the development of therapeutics that can prevent and/or repair the injured brain. We utilize two rodent models of brain injury: chronic hypoxia in the perinatal rodent and demyelination of the corpus callosum of the adult rodent. After hypoxia, we demonstrate no change in astrocyte cell number. Western blot analysis of white matter (WM) lysates show a decrease in glial fibrillary acidic protein (GFAP) expression and an increase in nestin expression after hypoxia, suggestive of an immature astrocytic phenotype. We examined expression of the two glial-specific glutamate transporters Glutamate Aspartate Transporter (GLAST) and Glutamate Transporter-1 (GLT-1) and observed a decrease in expression and function of both following hypoxia. JAK/STAT signaling is a critical pathway for astrocyte development and controls the onset of GFAP expression. We observed decreases in expression of pJAK1, pJAK2 and pSTAT3 following hypoxia and exposure of primary astrocyte cultures to hypoxia we confirmed that this effect was astrocyte-specific. To determine if disruptions in JAK/STAT signaling had any affect on GLAST or GLT-1 expression we exposed primary astrocytes to JAK Inhibitor I and observed a specific effect on GLAST expression. We treated perinatal mice with the JAK/STAT inhibitor AG490 which decreased GFAP, GLAST and the JAK/STAT signaling pathway with no effect on GLT-1. Using a GAD65-GFP transgenic mouse, we demonstrate that after demyelination there are GFP+ cells, traditionally thought to be destined for a neuronal lineage, in the lesion area expressing markers of oligodendrocytes. These cells originate in the subventricular zone (SVZ) where the BMP antagonist, chordin, is over-expressed following demyelination; chordin is responsible for the lineage plasticity observed. Using a GFAP-Cre and GAD65-Cre mouse lines to perform genetic fate mapping after hypoxia, we demonstrate an increased number of reporter-positive cells in the WM and an increased percentage that express the oligodendrocyte markers Olig2, NG2 and CC1. We show an increase the chemorepellent molecule, netrin, in the SVZ after hypoxia. Overall, these findings have important implications in understanding the cellular and molecular mechanisms that are involved in brain pathologies.
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