Toll-like receptor 4 (TLR4) plays a critical role in innate immunity that recognize pathogenic molecules and trigger inflammatory response. However, excessive activation of TLR4 activation may contribute to pathogenesis of autoimmune and inflammatory diseases. Therefore, the negative regulation of TLR4-triggered inflammatory response has attracted much attention in recent years. Activation of TLR4 signaling pathways by lipopolysaccharide (LPS) leads to the production of a broad array of cytokines and mediators that coordinate the immune response. Glia maturation factor gamma (GMFG), a member of the ADF/cofilin family of proteins that regulate actin cytoskeleton reorganization, is preferentially expressed in inflammatory cells, but its function in macrophages immune response remains unclear. In this study, we investigated whether GMFG participates in the molecular events underlying the inflammatory reaction to LPS in macrophages by knockdown of GMFG using small-interfering RNA approach. We have demonstarted that knockdown of GMFG significantly enhanced LPS-induced production of proinflammatory cytokines and chemokines, including TNF-alpha, IL-1beta, IL-8, and MCP-1 in human peripheral blood monocytes-derived macrophage as determined by quantitative real time-PCR and confirmed by enzyme-linked immunosorbent assay. Silencing of GMFG expression potentiates LPS-induced activation of p38, ERK1/2 and NF-kappaB signaling pathways by Western blot analysis. Moreover, luciferase assay revealed that gene silencing of GMFG promoted LPS-induced NF-kappaB activity for 2.5- to 4-fold. Furthermore, we found that TLR4 protein expression level were higher in GMFG-silenced macrophage compared with that of the control siRNA-transfected macrophages after stimulated with LPS for 1 hour. These results suggest that GMFG negatively regulation of TLR4 signaling-induced inflammatory cytokines by modulation of TLR4 expression levels and its down-stream NF-kappaB and p38 MAPK signaling pathway. In summary, we report that GMFG, in macrophage, function as a novel negative regulator that participates in the regulation of TLR4-signaling pathway, implicating that macrophage-specific modulation of GMFG may be beneficial in the treatment of inflammation as well as autoimmune disease.
