Glia maturation factor-gamma modulation of signaling pathways in macrophages

TLR4信号必须受到严格的调控，以提供有效的免疫保护和避免炎症诱导的病理。因此，对TLR4触发的炎症反应进行负性调节的机制尤为重要。胶质细胞成熟因子(GMFG)是一种新的肌动蛋白解聚因子/cofilin超家族蛋白，表达于炎症细胞中，参与介导中性粒细胞和T细胞的迁移，但其在巨噬细胞免疫反应中的作用尚不清楚。本研究在THP-1巨噬细胞和人原代巨噬细胞中研究了GMFG在脂多糖诱导的TLR4信号通路中的作用。内毒素刺激巨噬细胞可降低GMFG基因和蛋白的表达。我们发现GMFG对脂多糖诱导的人巨噬细胞中的NF-、B-、MAPK-和IRF3-信号通路的激活以及随后促炎细胞因子和I型干扰素的产生具有负性调节作用。我们发现内源性GMFG定位于早期和晚期的内吞体内。GMFG基因敲除延迟了内毒素诱导的TLR4内化，并导致TLR4在早期内吞体内滞留时间延长，提示TLR4从早期到晚期的转运被中断，这可能是内毒素诱导的TLR4信号增强的原因之一。综上所述，我们的研究结果表明，GMFG通过促进TLR4在巨噬细胞内的转运而发挥TLR4信号的负调节作用。

TLR4 signaling must be tightly regulated to provide both effective immune protection and avoid inflammation-induced pathology. Thus, the mechanisms that negatively regulate the TLR4-triggered inflammatory response are of particular importance. Glia maturation factor-γ (GMFG), a novel actin depolymerization factor/cofilin superfamily protein that is expressed in inflammatory cells, has been implicated in mediating neutrophil and T cell migration, but its function in macrophage immune response remains unclear. In the current study, the role of GMFG in the LPS-induced TLR4-signaling pathway was investigated in THP-1 macrophages and human primary macrophages. LPS stimulation of macrophages decreased GMFG mRNA and protein expression. We show that GMFG negatively regulates LPS-induced activation of NF-κB-, MAPK-, and IRF3-signaling pathways and subsequent production of proinflammatory cytokines and type I IFN in human macrophages. We found that endogenous GMFG localized within early and late endosomes. GMFG knockdown delayed LPS-induced TLR4 internalization and caused prolonged TLR4 retention at the early endosome, suggesting that TLR4 transport from early to late endosomes is interrupted, which may contribute to enhanced LPS-induced TLR4 signaling. Taken together, our findings suggest that GMFG functions as a negative regulator of TLR4 signaling by facilitating TLR4 endocytic trafficking in macrophages.