Signaling Events Involved in Macrophage Chemokine Expression in Response to Monosodium Urate Crystals

Abstract

Chemokine production has been associated with leukocyte infiltration into the joint during gouty arthritis, and monosodium urate (MSU) crystals, the causative agent of this arthropathy, have been shown to modulate their expression. In the present study, we investigated the transductional mechanisms underlying this cellular regulation in the murine macrophage cell line B10R. We report that MSU crystals rapidly and transiently increase mRNA levels of various chemokines in a concentration-dependent manner. Examination of second messenger activation revealed that macrophage exposure to MSU crystals led to MEK1/2, ERK1/2, and inhibitory protein B␣ phosphorylation as well as to NF-B and AP-1 nuclear translocation. Of interest, specific blockage of the ERK1/2 pathway drastically reduced up-modulation of MSU crystal-mediated chemokine production and activation of nuclear factors. Similarly, selective inhibition of NF-B suppressed NF-B DNA binding activity and the induction of all chemokine transcripts. These findings indicate that ERK1/2-dependent signals seem to be required for AP-1 and NF-B activation and subsequent mRNA expression of the various macrophage chemokines. In addition, transcription and stability assays performed in presence of actinomycin D showed that MSU crystal-mediated MIP-1␤ mRNA up-regulation resulted solely from transcriptional control, whereas that of MIP-1␣, MIP-2, and MCP-1 was due to both gene transcription activation and mRNA posttranscriptional stabilization. Overall, the results of this study help to define the molecular events that govern macrophage chemokine regulation in response to MSU crystals, which is of paramount importance to better understand, and eventually to tame, the inflammatory response during acute gout.

Rapid CCL2 Release by Membrane Stromal Cells Initiates Monosodium Urate Crystal-Induced Monocyte Recruitment in a Peritoneal Model of Gouty Inflammation

“…MSU crystals have been shown to induce upregulation and post-translational stabilisation of CCL2 mRNA in vitro (33) whereas synoviocytes and mesothelial cells appear to possess stores of MCP-I ready for immediate release upon MSU crystal stimulation (13,16). This differential regulation of CCL2 production may be one reason why only membrane CCL2 production was observed during the first 8 hours of MSU crystal stimulation in this study.…”

Induction of triggering receptor expressed on myeloid cells 1 in murine resident peritoneal macrophages by monosodium urate monohydrate crystals

“…TREM-1-mediated tyrosine phosphorylation, activation of MAPK, and mobilization of Ca 2ϩ might also lead to the activation of transcription complexes, which could have a synergistic effect with NF-B in promoting the expression of proinflammatory genes. It has also been shown that MSU crystals potentially activate the NF-B signaling pathway (23). Overall, these findings suggest that TREM-1 may act synergistically with MSU crystals in promoting the production of proinflammatory cytokines through activation of NF-B and MAPK, tyrosine phosphorylation, and mobilization of Ca 2ϩ .…”

Innate immunity conferred by toll-like receptors 2 and 4 and myeloid differentiation factor 88 expression is pivotal to monosodium urate monohydrate crystal-induced inflammation

“…TLRs are type I transmembrane receptors characterized by the presence of extracellular leucine-rich repeat motifs that recognize pathogenassociated molecular patterns (26). Most TLRs have a cytoplasmic Toll/IL-1 receptor (IL-1R) domain, which is required for the activation of downstream signaling pathways that lead to the activation of NF-B (26), a transcription factor activated rapidly by MSU crystals and centrally involved in MSU crystal-induced cell activation (27,28). In response to pathogen-associated molecular patterns, the canonical TLR signaling pathway recruits the cytosolic TLR adapter protein myeloid differentiation factor 88 (MyD88), IL-1R-activated kinase, and TNF receptor-associated factor 6 to activate IKKs, and the process culminates in NF-B-mediated expression of proinflammatory messenger RNA (26).…”