Research article
High-density lipoproteins downregulate CCL2 production in human fibroblast-like synoviocytes stimulated by urate crystals
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* Corresponding author: Anna Scanu anna.scanu@unipd.it
- † Equal contributors
1 Department of Clinical and Experimental Medicine, University of Padova, Via Giustiniani 2, 35128 Padova, Italy
2 Division of Immunology and Allergy, Hans Wilsdorf Laboratory, IARG Department of Internal Medicine, University Hospital and Faculty of Medicine, University of Geneva, 4 rue Gabrielle-Perret-Gentil, CH-1211 Geneva 14, Switzerland
3 Department of Medical and Surgical Specialties, Orthopaedic Clinic, University of Padova, via Giustiniani 3, 35128 Padova, Italy
Arthritis Research & Therapy 2010, 12:R23 doi:10.1186/ar2930
Published: 11 February 2010Abstract
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)-1β (10 pg/ml) in the presence or absence of HDL (50 and 100 μg/ml). The production and expression of CCL2 was evaluated with 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 μg/ml MSU crystals and 20 to 24 hours. 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 with 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-1β, suggesting a direct effect of HDL on the FLS activation state.
Conclusions
The present results demonstrate that MSU crystals induce FLS to release CCL2 that is stored in vesicles in 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 antiinflammatory functions of HDL, which might play a part in the limitation of acute gout attack.