Ito Takuji, Morita Tokiko, Yoshida Kenji, Negishi Takayuki, Yukawa Kazunori
Department of Physiology, Faculty of Pharmacy, Meijo University, Nagoya 468-8503, Japan.
Int J Mol Med. 2014 Jun;33(6):1635-42. doi: 10.3892/ijmm.2014.1727. Epub 2014 Apr 4.
Semaphorin family members have been identified as axonal guidance molecules that mediate the directional determination for axonal elongation during neuronal development. Several semaphorins have been shown to play crucial roles for various immune response phases. In a previous study using knockout mice, we suggested that Plexin-A1, a Semaphorin 3A (Sema3A) receptor, is involved in the increased production of inflammatory factors such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in the murine microglial response to lipopolysaccharide (LPS). In that study, Sema3A-Plexin-A1 signaling was also shown to have crosstalk with Toll-like receptor 4 (TLR4) signaling to increase nitric oxide production, although the specific intracellular signaling molecule involved in the NO increase was not identified. By investigating the role of Plexin-A1 in the response of the BV-2 microglial cell line to LPS, in the present study novel findings regarding the influence of Plexin-A1 activation on TLR4 signaling in microglial cells were investigated. First, the production of inflammatory markers such as inducible nitric oxide synthase (iNOS), IL-1β and TNF-α in the response to TLR4 stimulation was significantly decreased in BV-2 cells with the knockdown of Plexin-A1. Accordingly, Plexin-A1 was required for the enhanced production of inflammatory factors induced by LPS in BV-2 microglial cells. Second, Plexin-A1 signaling in BV-2 cells showed crosstalk with the LPS-induced TLR4 pathway through activation of nuclear factor-κB (NF-κB) and extracellular signal‑regulated kinase (ERK). Third, LPS-induced NO production in BV-2 cells was intensified by Sema3A-Plexin-A1 signaling in an ERK1/2 activation-dependent manner. This finding suggested the crucial role of Plexin-A1 signaling through ERK activation in TLR4 activation-induced NO production in BV-2 microglial cells. These results therefore suggest that Plexin-A1 and Sema3A are possible new targets for treating LPS-induced encephalopathy and neuroinflammation-related mental disorders.
信号素家族成员已被确定为轴突导向分子，可在神经元发育过程中介导轴突伸长的方向确定。已有研究表明，几种信号素在各种免疫反应阶段发挥关键作用。在之前一项使用基因敲除小鼠的研究中，我们发现信号素3A（Sema3A）受体丛状蛋白A1（Plexin-A1）参与了小鼠小胶质细胞对脂多糖（LPS）反应中炎性因子如白细胞介素-1β（IL-1β）和肿瘤坏死因子-α（TNF-α）产生的增加。在该研究中，还表明Sema3A-Plexin-A1信号通路与Toll样受体4（TLR4）信号通路存在串扰，以增加一氧化氮的产生，尽管未确定参与一氧化氮增加的具体细胞内信号分子。通过研究Plexin-A1在BV-2小胶质细胞系对LPS反应中的作用，本研究调查了关于Plexin-A1激活对小胶质细胞中TLR4信号通路影响的新发现。首先，在Plexin-A1敲低的BV-2细胞中，对TLR4刺激反应时炎性标志物如诱导型一氧化氮合酶（iNOS）、IL-1β和TNF-α的产生显著降低。因此，Plexin-A1是BV-2小胶质细胞中LPS诱导的炎性因子产生增加所必需的。其次，BV-2细胞中的Plexin-A1信号通路通过激活核因子-κB（NF-κB）和细胞外信号调节激酶（ERK）与LPS诱导的TLR4途径显示出串扰。第三，Sema3A-Plexin-A1信号通路以ERK1/2激活依赖性方式增强了BV-2细胞中LPS诱导的一氧化氮产生。这一发现表明Plexin-A1信号通路通过ERK激活在BV-2小胶质细胞中TLR4激活诱导的一氧化氮产生中起关键作用。因此，这些结果表明Plexin-A1和Sema3A可能是治疗LPS诱导的脑病和神经炎症相关精神障碍的新靶点。
