STAT3 signaling after traumatic brain injury.

Astrocytes respond to trauma by stimulating inflammatory signaling. In studies of cerebral ischemia and spinal cord injury, astrocytic signaling is mediated by the cytokine receptor glycoprotein 130 (gp130) and Janus kinase (Jak) which phosphorylates the transcription factor signal transducer and activator of transcription-3 (STAT3). To determine if STAT3 is activated after traumatic brain injury (TBI), adult male Sprague-Dawley rats received moderate parasagittal fluid-percussion brain injury or sham surgery, and then the ipsilateral cortex and hippocampus were analyzed at various post-traumatic time periods for up to 7 days. Western blot analyses indicated that STAT3 phosphorylation significantly increased at 30 min and lasted for 24 h post-TBI. A significant increase in gp130 and Jak2 phosphorylation was also observed. Confocal microscopy revealed that STAT3 was localized primarily within astrocytic nuclei. At 6 and 24 h post-TBI, there was also an increased expression of STAT3 pathway-related genes: suppressor of cytokine signaling 3, nitric oxide synthase 2, colony stimulating factor 2 receptor β, oncostatin M, matrix metalloproteinase 3, cyclin-dependent kinase inhibitor 1A, CCAAT/enhancer-binding protein β, interleukin-2 receptor γ, interleukin-4 receptor α, and α-2-macroglobulin. These results clarify some of the signaling pathways operative in astrocytes after TBI and demonstrate that the gp130-Jak2-STAT3 signaling pathway is activated after TBI in astrocytes.