Distinct macrophage polarization in acute and chronic gout

Macrophage polarization mediates the development of inflammatory diseases. However, the polarization status at various stages of gout is not fully understood. Our study aimed to define the evolution of macrophage polarization in acute and chronic gout. Normal human synovium and synovium with tophi were collected for immunofluorescence (IF). Rat gouty joints were collected for joint thickness assessment and pathological evaluation. Tissue mRNA expression of inducible nitric oxide synthase (iNOS) and arginase-1 (Arg-1) were evaluated. Mouse peritoneal macrophages and THP-1 derived macrophages were stimulated by monosodium urate (MSU) crystals and were collected for detection of interleukin (IL) -1 beta and IL-37 levels and iNOS/Arg-1 ratio. Arg-1 and IL-37 were highly expressed in normal synovium and synovium with tophi. In rat gouty joints, the inflammatory cell counts and ankle thickness began to increase at 2 h, peaked at 24 h, and was decreased spontaneously. An increase in macrophages preceded the neutrophils infiltration. Infiltration of M1 was positively related with the severity of arthritis. M2 appeared in an early stage (at 2 h) of inflammation. The number of M1 macrophages was comparable to that of M2 from 2 to 12 h and exceeded M2 number at 18 h and 24 h. The ratios of M2/M1 reversed at 48 h and remained reversed until 120 h. In mice gouty joints, iNOS/Arg-1 mRNA ratio was significantly higher than the that in control group at 8 h. The proportion of neutrophils and M1-macrophages reached peak at 4 h in mice model with peritoneal gout. Concentration of IL-1 beta and ratio of iNOS/Arg-1 were increased at 6 h, peaked at 48 h, and were then decreased at 72 h in vitro, while the concentration of IL-37 peaked at 2 h and then decreased. In summary, altered macrophage polarization was observed in various stages of gouty inflammation. Macrophages in acute gout were polarized into M1 at early stage and into M2 at later stage while the macrophages in chronic gout mainly were only polarized towards M2. The number of M1 rose with the progression of inflammation. Early increase of M2 was observed, which might be generated directly from M0. Characterization of macrophage polarization into different functional phenotypes is valuable for further investigation of gout pathogenesis, as well as for a better disease management. In this study the authors found that altered macrophage polarization exists in various stages of gouty inflammation. Macrophages in acute gout were polarized into M1 at an early stage and into M2 at later stages while the macrophages in chronic gout were generally polarized towards M2. The number of M1 rose with the progression of inflammation. Early increase of M2 was observed, which might be generated directly from M0.

Automated summary

This study found altered macrophage polarization in different stages of gouty inflammation. In acute gout, macrophages were polarized into M1 at an early stage and into M2 at later stages, while in chronic gout, macrophages were mainly polarized towards M2. The number of M1 increased with the progression of inflammation. An early increase of M2 was also observed, which might be generated directly from M0.