Gene Network Revealed Involvements of Birc2, Birc3 and Tnfrsf1a in Anti-Apoptosis of Injured Peripheral Nerves

Crush injury or axotomy of peripheral nerves results in the rapid production of the inflammatory cytokines, which were confirmed in various models, to some extent, to be noxious to the myelin sheath or Schwann cells (SCs). TNF-α is one of the primary initiators of the inflammatory cascade and exerts pleiotropic functions in the physiological conditions by binding to its receptors, type I (TNFRI) and type II (TNFRII). The pathway molecules TNFRI, Birc2 and Birc3 play key roles during the activation of the signaling. Injured peripheral nerves, preventing them from TNF-α-mediated destruction and proceeding to successful regeneration, might initiate an anti-apoptotic mechanism. To identity the exact functions of TNFRI, Birc2 and Birc3, as well as its involved pathways in the cellular events, we inferred a dynamic gene regulatory network from short time-series measurements of the proximal nerve segment cDNA microarray following rat sciatic nerve transection. TNFRI family member Tnfrsf1a, Birc2 and Birc3 were mined out integrating as master regulators to mediate inflammatory responses. Experiments revealed that Tnfrsf1a, Birc2 and Birc3 proteins colocalized with S100 in the rat peripheral nerve tissues, and the expression levels increased with the time extension. Knockdown of the proteins induced the apoptotic formation of primary cultured SCs by upregulation of caspase 3 and caspase 6. Our systematic analysis indicated that Tnfrsf1a, Birc2 and Birc3 of SCs, not originally regarded as XIAP, were mainly responsible for the inflammation-mediated anti-apoptosis of peripheral nerves. Birc2 and Birc3 might be the most potential targets for anti-apoptotic protection mediated by inflammatory cytokines.

周围神经挤压伤或轴突切断术后会快速诱导炎症因子的产生，多项模型实验已证实，此类炎症因子在一定程度上对髓鞘或施万细胞（Schwann Cells）具有毒性作用。肿瘤坏死因子α（TNF-α）是炎症级联反应的主要启动因子之一，在生理状态下可通过结合其两类受体——I型受体（TNFRI）与II型受体（TNFRII）——发挥多效性功能。通路分子TNFRI、Birc2与Birc3在该信号通路的激活过程中发挥关键作用。受损周围神经可通过启动抗凋亡机制，避免自身遭受肿瘤坏死因子α（TNF-α）介导的破坏，并最终实现成功再生。为明确TNFRI、Birc2与Birc3的具体功能，以及其在细胞事件中参与的信号通路，本研究通过对大鼠坐骨神经切断后近端神经段的cDNA微阵列短时间序列检测数据，推导得到了动态基因调控网络。研究筛选得到TNFRI家族成员Tnfrsf1a、Birc2与Birc3，并将其整合为介导炎症反应的核心调控因子。实验结果显示，Tnfrsf1a、Birc2与Birc3蛋白在大鼠周围神经组织中与S100蛋白共定位，且其表达水平随时间延长而上调。敲低上述蛋白可通过上调半胱天冬酶3（caspase 3）与半胱天冬酶6（caspase 6）的表达，诱导原代培养的施万细胞发生凋亡。本研究的系统性分析表明，施万细胞中的Tnfrsf1a、Birc2与Birc3（最初并未被归类为X连锁凋亡抑制蛋白（XIAP））主要负责介导炎症信号引发的周围神经抗凋亡过程。Birc2与Birc3有望成为炎症因子介导的抗凋亡保护治疗的最具潜力靶点。