Activation of JAK/STAT signalling in neurons following spinal cord injury in mice.
ABSTRACT The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signalling pathway is one of the most important in transducing signals from the cell surface to the nucleus in response to cytokines. In the present study, we investigated chronological alteration and cellular location of JAK1, STAT3, phosphorylated (p)-Tyr1022/1023-JAK1, p-Tyr705-STAT3, and interleukin-6 (IL-6) following spinal cord injury (SCI) in mice. Western blot analysis showed JAK1 to be significantly phosphorylated at Tyr1022/1023 from 6 h after SCI, peaking at 12 h and gradually decreasing thereafter, accompanied by phosphorylation of STAT3 at Tyr705 with a similar time course. ELISA analysis showed the concentration of IL-6 in injured spinal cord to also significantly increase from 3 h after SCI, peaking at 12 h, then gradually decreasing. Immunohistochemistry revealed p-Tyr1022/1023-JAK1, p-Tyr705-STAT3, and IL-6 to be mainly expressed in neurons of the anterior horns at 12 h after SCI. Pretreatment with a JAK inhibitor, AG-490, suppressed phosphorylation of JAK1 and STAT3 at 12 h after SCI, reducing recovery of motor functions. These findings suggest that SCI at the acute stage produces IL-6 mainly in neurons of the injured spinal cord, which activates the JAK/STAT pathway, and that this pathway may be involved with neuronal response to SCI.
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ABSTRACT: Injury to the spinal cord induces a complex cascade of cellular reactions at the local lesion area: secondary cell death and inflammatory reactions as well as scar and cavity formation take place. In order to investigate the molecular features underlying this local wounding response and to determine their pathophysiological implications, we studied the expression pattern of pro-inflammatory and chemoattractant cytokines in an experimental spinal cord injury model in mouse. We show by in situ hybridization that transcripts for the pro-inflammatory cytokines TNF alpha and IL-1 as well as the chemokines MIP-1alpha and MIP-1beta are upregulated within the first hour following injury. In this early phase, the expression of the pro-inflammatory cytokines is restricted to cells in the surroundings of the lesion area probably resident CNS cells. While TNF alpha is expressed in a very narrow time window, IL-1 can be detected in a second phase in a subset of polymorphonuclear granulocytes which immigrate into the spinal cord around 6 h. Message for the chemokines MIP-1alpha and beta is expressed in a generalized way in the grey matter of the entire spinal cord around 24 h and gets again restricted to the cellular infiltrate at the lesion site at 4 days following injury. Interestingly, our data suggest that resident CNS cells, most probably microglial cells, and not peripheral inflammatory cells, are the main source for cytokine and chemokine mRNAs. The defined cytokine pattern observed indicates that the inflammatory events upon lesioning the CNS are tightly controlled. The very early expression of pro-inflammatory cytokine and chemokine messages may represent an important element of the recruitment of inflammatory cells. Additional pathophysiological consequences of the specific cytokine pattern observed remain to be determined.European Journal of Neuroscience 08/1997; 9(7):1422-38. · 3.75 Impact Factor
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ABSTRACT: JAK/STAT is one of the pathways bearing signals from the cell membrane to the nucleus in response to extracellular growth factors and cytokines. In the present study, we examined the cellular distribution of Jak1 and Stat3, and activation of the JAK/STAT pathway following transient focal cerebral ischemia in the rat. Jak1 was mainly seen in white matter astrocytes and in certain neurons. Notably, large pyramidal neurons of cortical layer V showed the highest neuronal Jak1 expression within cerebral cortex and, in addition, expressed Stat3 indicating that the JAK/STAT pathway is involved in signaling in the corticofugal projection system. Shortly following ischemia, Jak1 immunoreactive astrocytes located in the ipsilateral neighbouring white matter and ischemic cortex and striatum showed nuclear translocation of Stat3. These features were maintained in large reactive astrocytes that surrounded the infarct from 3 to 7 days. At these later times, the abundant reactive microglia/macrophages were strongly immunoreactive to Stat3 and, to a lesser extent, Jak1. Two main protein complexes showing DNA binding activity at the sis-inducible element site were found under basal conditions, followed by changes in this pattern following ischemia concomitant with neuronal cell loss and activation of glia. This study showed basal cerebral activity of JAK/STAT signaling pathway, involving Jak1 and Stat3 proteins, and selective activation following ischemia. It is suggested that the kinase activity of Jak1 mediates nuclear translocation of Stat3 in astrocytes, and that this signaling pathway is involved in the astroglial response to focal cerebral ischemia.Glia 06/2000; 30(3):253-70. · 5.07 Impact Factor
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ABSTRACT: To determine whether the pathophysiological processes after transient forebrain ischemia are mediated via a signal pathway involving gp130 (a signal transducer for the interleukin-6 family), we analyzed changes in the expression of gp130 and its downstream transcription factor, signal transducer and activator of transcription factor 3 (STAT3), in the rat hippocampus of a four-vessel occlusive ischemia model. Expression of gp130 mRNA was restricted to neurons of the pyramidal cell and granule cell layers in control animals. Four hours after ischemic injury, astrocytes expressed gp130 mRNA. Expression of gp130 increased preferentially in the CA1 and dentate hilar regions, and was maintained for at least 2 weeks. Increase in gp130 expression was accompanied by the activation of STAT3 following ischemic injury. Four hours after injury, STAT3 and phosphorylated STAT3 (pSTAT3) were observed in the nuclei of the dentate hilar region, and sequentially in the CA1 region at day 1. By day 3, STAT3 immunoreactivity markedly increased in these areas, where small cells with the morphology of astrocytes showed nuclear and cytoplasmic STAT3 and nuclear pSTAT3 immunoreactivities. These patterns were especially maintained in the CA1 area until 14 days of reperfusion. Double-labeling experiments revealed that the cells expressing STAT3 and pSTAT3 were glial fibrillary acidic protein-expressing reactive astrocytes. These results show a coordinated and long-lasting upregulation of gp130 mRNA and STAT3 activation in reactive astrocytes of the postischemic hippocampus, indicating that they may be involved in the astrocytic response to an ischemic insult.Glia 03/2003; 41(3):237-46. · 5.07 Impact Factor