ABSTRACT: ABSTRACT: INTRODUCTION: To investigate whether monosodium urate (MSU) crystals induce the production of CCL2 (monocyte chemoattractant protein-1; MCP-1) in human fibroblast-like synoviocytes (FLS) and whether this mechanism would be affected by high-density lipoproteins (HDL). METHODS: Human FLS isolated from synovial tissue explants were stimulated with MSU crystals (0.01 to 0.5 mg/ml) or interleukin (IL)-1beta (10 pg/ml) in the presence or absence of HDL (50 and 100 ug/ml). The production and expression of CCL2 was evaluated by ELISA, confocal microscopy, immunofluorescence microscopy, chemotaxis assay, and real-time quantitative PCR. RESULTS: Exposure of FLS to MSU crystals induced CCL2 accumulation in culture medium in a dose- and time-dependent manner reaching a plateau at 50 to 75 ug/ml MSU crystals and 20 to 24h. Although low, the induced CCL2 levels were sufficient to trigger mononuclear cell migration. In resting FLS, CCL2 was localized in small cytoplasmic vesicles whose number diminished upon MSU crystal-stimulation. Concomitantly, MSU crystals triggered the induction of CCL2 mRNA expression. All these processes were inhibited by HDL which cause a 50% decrease in CCL2 mRNA levels and a dose-dependent inhibition of the release of CCL2. Similar results were obtained when FLS were pretreated with HDL and washed before activation by MSU crystals or IL-1beta, suggesting a direct effect of HDL on FLS activation state. CONCLUSIONS: The present results demonstrate that MSU crystals induce FLS to release CCL2 that is stored in vesicles upon resting conditions. This mechanism is inhibited by HDL which may limit the inflammatory process by diminishing CCL2 production and in turn monocytes/macrophages recruitment in joints. This study confirms the anti-inflammatory functions of HDL which might play a part in the limitation of acute gout attack
Arthritis Res.Ther. 12(1).