Reactive gliosis is a hallmark of disease-, trauma-, and chemical-induced damage to the CNS. This response is characterized by activation of microglia and astrocytes at sites of damage. Signaling pathways associated with the induction of gliosis remain elusive, but recent evidence implicates the Janus kinase (JAK)-signal transducer and activator of transcription-3 (STAT3) pathway. This pathway is a down-stream effector of cytokines linked to injury-induced astroglial activation and subsequent expression of GFAP, a cellular response that appears to require STAT3 phosphorylation. Here, we seek to further characterize gliosis by elucidating ligands involved in STAT3 phosphorylation and the induction of GFAP. Two injury models were employed. First we administered, in vivo, saline or the dopaminergic neurotoxin, 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP, 12.5mg/kg, sc). 12 hours post-treatment, coronal slices of striatum were examined for STAT3 phosphorylation and cytokine production. pSTAT3 was present in MPTP treated animals while absent in controls. Messenger RNA for gp130 cytokines [leukemia inhibitory factor (LIF) and oncostatin M (OSM)] as well as a glial-derived chemokine (CCL-2/MCP-1) was induced in MPTP treated animals. Striatal slices were then incubated in oxygenated buffer. Within 45 minutes, control striata also expressed p-STAT3 indicating that STAT3 activation can result from slice injury. To confirm the induction of pSTAT3 in vivo, stab wounds were made in striata of mice. GFAP was induced 48 hours after stab and this effect was preceded by pSTAT3 expression. In addition, mRNA for LIF, OSM, and MCP-1 was induced by 24 hours. Since these three ligands were upregulated in both damage models, they were incubated 45 minutes with untreated slices and slices were then assayed for pSTAT3. LIF and OSM promoted glial activation as evidenced by increased pSTAT3 and GFAP protein whereas CCL-2 inhibited gliosis. Together, these data suggest that glial chemokines and gp130 cytokines mediate/modulate reactive gliosis and that pSTAT3 is an early event in glial activation in both neurotoxic and mechanical injury.
The Toxicologist. Society of Toxicology 44th Annual Meeting and ToxExpo, March 6-10, 2005, New Orleans, Louisiana