Reactive gliosis is the most prominent response to diverse forms or central nervous system injury. The signaling events that mediate this characteristic response to neural injury are under intense investigation. Several studies have demonstrated the activation of phosphoproteins within the mitogen-activated protein kinase (MAPKs) and Janus kinase (JAK) pathways following neural insult. These signaling pathways may be important and responsible for the glial response following injury, by virtue of their ability to phosphorylate and regulate the activity of various transcription factors. This study thought to delineate, in vivo, the relative contribution and temporal activation of MAPK-and JAK-related signaling components to the gliotic response, as measured by induction of glial-fibrillary acidic protein (GFAP), following chemical-induced neural damage. At various timepoints (1h, 3h, 6h, 12h, 24h, 48h, 72h, 2wk and 3wk) following methamphetamine (METH, 10mg/kg x 4) administration, female C57BL/6J mice were sacrificed by focused microwave irradiation, to preserve steady state phosphorylation. Striatal (target) and non-target (hippocampal) homogenates were assayed for METH-induced changes in markers of dopamine neuron integrity as well as differences in the levels of activated phosphoproteins. GFAP up regulation occurred as early as 6h, reached a maximum at 72h, and was declining 2wk following METH exposure. Neurotoxicant-induced reductions in striatal levels of dopamine and tyrosine hydroxylase paralleled the temporal profile of GFAP induction. Blots of striatal homogenates, probed with phosphorymoon-state specific antibodies, demonstrated significant changes in activated forms MAPK, JNK, MEK1/2, p70S6, CREB, and STAT3 as early as one hour after injection, with the largest activation at timepoints (6 and 12h) preceeding the peak induction of GFAP (72h). These results implicate up-stream effectors of the 130/GF-RAS pathway in the induction of gliosis, which may serve as potential targets for modulation of the glial response to neural damage.
The Toxicologist. Society of Toxicology 40th Annual Meeting, March 25-29, 2001, San Francisco, California