Protective Role of STAT3 in NMDA and Glutamate-Induced Neuronal Death: Negative Regulatory Effect of SOCS3

The present study investigates the involvement of the IL-6 family of cytokines, activation of the transcription factor Signal Transducer and Activator of Transcription-3 (STAT3), and the role of Suppressor Of Cytokine Signaling-3 (SOCS3) in regulating excitotoxic neuronal death in vitro. Biochemical evidence demonstrates that in primary cortical neurons and SH-SY5Y neuroblastoma cells, IL-6 cytokine family members, OSM and IL-6 plus the soluble IL-6R (IL-6/R), prevent NMDA and glutamate-induced neuronal toxicity. As well, OSM and IL-6/R induce tyrosine and serine phosphorylation of STAT3 in primary cortical neurons and SH-SY5Y cells. Studies using Pyridine 6 (P6), a pan-JAK inhibitor, demonstrate that the protective effect of OSM and IL-6/R on neuronal death is mediated by the JAK/STAT3 signaling pathway. In parallel to STAT3 phosphorylation, OSM and IL-6/R induce SOCS3 expression at the mRNA and protein level. P6 treatment inhibits SOCS3 expression, indicating that STAT3 is required for OSM and IL-6/R-induced SOCS3 expression. Lentiviral delivery of SOCS3, an inhibitor of STAT3 signaling, into primary neurons and SH-SY5Y cells inhibits OSM and IL-6/R-induced phosphorylation of STAT3, and also reverses the protective effect of OSM and IL-6/R on NMDA and glutamate-induced neurotoxicity in primary cortical neurons. In addition, treatment with IL-6 cytokines increases expression of the anti-apoptotic protein Bcl-xL and induces activation of the Akt signaling pathway, which are also negatively regulated by SOCS3 expression. Thus, IL-6/R and OSM-induced SOCS3 expression may be an important factor limiting the neuroprotective effects of activated STAT3 against NMDA and glutamate-induced neurotoxicity.

本研究探讨了白细胞介素-6（IL-6）细胞因子家族、转录因子信号转导与转录激活因子3（STAT3）的激活，以及细胞因子信号转导抑制因子3（SOCS3）在体外调控兴奋性毒性神经元死亡中的作用。生化实验证据显示，在原代皮层神经元与SH-SY5Y神经母细胞瘤细胞中，IL-6细胞因子家族成员抑癌素M（OSM）、IL-6联合可溶性IL-6受体（IL-6/R），可拮抗N-甲基-D-天冬氨酸（NMDA）与谷氨酸诱导的神经元毒性。同时，OSM与IL-6/R可在原代皮层神经元及SH-SY5Y细胞中诱导STAT3发生酪氨酸与丝氨酸磷酸化。采用泛JAK抑制剂吡啶6（Pyridine 6，P6）开展的研究证实，OSM与IL-6/R对神经元死亡的保护作用由JAK/STAT3信号通路介导。与STAT3磷酸化同步，OSM与IL-6/R可在mRNA与蛋白水平诱导SOCS3的表达。P6处理可抑制SOCS3的表达，提示STAT3是OSM与IL-6/R诱导SOCS3表达所必需的。将STAT3信号通路的抑制剂SOCS3通过慢病毒递送至原代神经元与SH-SY5Y细胞后，可抑制OSM与IL-6/R诱导的STAT3磷酸化，同时逆转OSM与IL-6/R对原代皮层神经元中NMDA及谷氨酸诱导的神经毒性的保护作用。此外，IL-6细胞因子处理可上调抗凋亡蛋白Bcl-xL的表达，并激活Akt信号通路，而这两种效应同样受SOCS3的负向调控。综上，IL-6/R与OSM诱导的SOCS3表达，可能是限制激活的STAT3对抗NMDA及谷氨酸诱导神经毒性的神经保护作用的关键调控因素。