TLR7 Negatively Regulates Dendrite Outgrowth through the Myd88-c-Fos-IL-6 Pathway
TLR7 Negatively Regulates Dendrite Outgrowth through the Myd88-c-Fos-IL-6 Pathway
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DOI：
10.1523/jneurosci.5566-12.2013
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发表时间：
2013-07-10
影响因子：
5.3
通讯作者：
Hsueh, Yi-Ping
中科院分区：
文献类型：
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作者：
Liu, Hsin-Yu;Hong, Yun-Fen;Hsueh, Yi-Ping
Toll样受体（TLR）识别病原体和病原体相关的分子模式，并诱导先天性免疫反应。一些TLR在神经元中表达并调节神经发育和神经变性。然而，TLR在神经元中的下游信号通路和效应器仍然存在争议。在这份报告中，我们提供的证据表明，TLR 7负调控树突生长通过典型的髓样分化初级反应基因88（Myd 88）-c-Fos-白细胞介素（IL）-6途径。尽管TLR 7和TLR 8都识别单链RNA（ssRNA），但定量逆转录PCR的结果表明，TLR 7是脑中识别ssRNA的主要TLR。在体外培养和子宫内电穿孔实验中，TLR 7表达水平的操纵足以改变神经元形态，表明存在内在TLR 7配体。此外，RNA酶A处理，去除ssRNA在培养物中促进树突生长。我们还发现，向培养的神经元中加入ssRNA和合成的TLR 7激动剂CL 075和洛索立宾，而不是R837（咪喹莫特），通过TLR 7特异性地限制树突生长。这些结果都表明TLR 7负调控神经元分化。在培养的神经元中，TLR 7激活通过Myd 88诱导IL-6和TNF-α表达。使用Myd 88-，IL-6-，和TNF-α-缺陷的神经元，我们然后证明了Myd 88和IL-6，但不是TNF-α，在TLR 7途径中的重要作用，以限制树突生长。除了神经元的形态，TLR 7基因敲除也影响小鼠的行为，因为类似于2周龄的年轻突变小鼠在开阔视野中表现出明显较低的探索活动。总之，我们的研究表明，TLR 7负调控树突的生长和影响小鼠的认知。
Toll-like receptors (TLRs) recognize both pathogen-and danger-associated molecular patterns and induce innate immune responses. Some TLRs are expressed in neurons and regulate neurodevelopment and neurodegeneration. However, the downstream signaling pathways and effectors for TLRs in neurons are still controversial. In this report, we provide evidence that TLR7 negatively regulates dendrite growth through the canonical myeloid differentiation primary response gene 88 (Myd88)-c-Fos-interleukin (IL)-6 pathway. Although both TLR7 and TLR8 recognize single-stranded RNA (ssRNA), the results of quantitative reverse transcription-PCR suggested that TLR7 is the major TLR recognizing ssRNA in brains. In both in vitro cultures and in utero electroporation experiments, manipulation of TLR7 expression levels was sufficient to alter neuronal morphology, indicating the presence of intrinsic TLR7 ligands. Besides, the RNase A treatment that removed ssRNA in cultures promoted dendrite growth. We also found that the addition of ssRNA and synthetic TLR7 agonists CL075 and loxoribine, but not R837 (imiquimod), to cultured neurons specifically restricted dendrite growth via TLR7. These results all suggest that TLR7 negatively regulates neuronal differentiation. In cultured neurons, TLR7 activation induced IL-6 and TNF-alpha expression through Myd88. Using Myd88-, IL-6-, and TNF-alpha-deficient neurons, we then demonstrated the essential roles of Myd88 and IL-6, but not TNF-alpha, in the TLR7 pathway to restrict dendrite growth. In addition to neuronal morphology, TLR7 knockout also affects mouse behaviors, because young mutant mice similar to 2 weeks of age exhibited noticeably lower exploratory activity in an open field. In conclusion, our study suggests that TLR7 negatively regulates dendrite growth and influences cognition in mice.