Molecular mechanism of cerebral ischemia through Jak-Stat signaling

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Introduction :Cerebral ischemia induces the expression of a number of growth factors and cytokines that can protect neurons against ischemic brain injury. For example, ciliary neurotrophic factor (CNTF), epidermal growth factor (EGF) and interleukin-6 (IL-6) have been shown to promote Stat3 activation. These growth factors and cytokines can activate Janus protein tyrosine kinases (Jaks)/signal transducers and activators of transcription (Stat) pathways. Recently, we reported that Stat3 was activated following cerebral ischemia in mouse [1]. However, little is known about the function of activated Stat3 in the ischemic brain. Here we demonstrate the increased expression of activated Stat3 promotes cell death in cultured astrocyres.Methods & Results :Astrocytes from the forebrains of newborn rats were cultured. Recombinant adenovirus expressing Stat3 wild type (St3.Wt), Stat3 dominant negative type (St3.DN) and LacZ were constructed as described previously [2]. Astocytes were exposed to … More adenovirus vector expressing Stat3.Wt, Stat3.DN or LacZ (multiplicity of infection 10) for 2h and incubated with a virus free fresh medium up to 72h. Three days later, inoculation with the virus vectors expressing St3.wt and St3.DN remarkably induced Stat3 protein compared with the control (LacZ). Western blots also revealed that Ad.St3.wt remarkably induced p-Stat3(Tyr-705) while Ad.St3.DN and Ad.LacZ did not. These results demonstrated that both Ad.St3.Wt and Ad.St3.DN induced Stat3 protein in cultured astrocytes and that only Ad.St3.Wt could phosphorylate Stat3 at Tyr-705 site and activate Stat3. LDH assay revealed that overexpression of St3.wt promoted cell death while overexpression of St3.DN and LacZ did not. In addition, caspase-3 like activity of the St3.Wt treated group was significantly increased than that of the St3.DN group at 2d after virus inoculation.Conclusion :We have shown that over-expression of Stat3 promotes cell death in cultured astrocytes, and activation of caspase-3 activity may be involved in this cell death mechanism. These data have revealed that activation of Stat3 can play a crucial role in the mechanism of ischemic cell death.References :[1]Wen et al. ; Neurosci Lett, 303:153-156, (2001)[2]Nakajima et al. ; EMBO J, 15:3651-58 (1996) Less