Myeloid deletion of SIRT1 suppresses collagen-induced arthritis in mice by modulating dendritic cell maturation

The type III histone deacetylase silent information regulator 1 (SIRT1) is an enzyme that is critical for the modulation of immune and inflammatory responses. However, the data on its role in rheumatoid arthritis (RA) are limited and controversial. To better understand how SIRT1 regulates adaptive immune responses in RA, we evaluated collagen-induced arthritis (CIA) in myeloid cell-specific SIRT1 knockout (mSIRT1 KO) and wild-type (WT) mice. Arthritis severity was gauged on the basis of clinical, radiographic and pathologic scores. Compared with their WT counterparts, the mSIRT1 KO mice exhibited less severe arthritis, which was less destructive to the joints. The expression levels of inflammatory cytokines, matrix metalloproteinases and ROR-γT were also reduced in the mSIRT1 KO mice compared with the WT mice and were paralleled by reductions in the numbers of Th1 and Th17 cells and CD80- or CD86-positive dendritic cells (DCs). In addition, impaired DC maturation and decreases in the Th1/Th17 immune response were observed in the mSIRT1 KO mice. T-cell proliferation was also investigated in co-cultures with antigen-pulsed DCs. In the co-cultures, the DCs from the mSIRT1 KO mice showed decreases in T-cell proliferation and the Th1/Th17 immune response. In this study, myeloid cell-specific deletion of SIRT1 appeared to suppress CIA by modulating DC maturation. Thus, a careful investigation of DC-specific SIRT1 downregulation is needed to gauge the therapeutic utility of agents targeting SIRT1 in RA. Mice lacking a key immune-regulating enzyme are less prone to develop rheumatoid arthritis. A research team led by Sang-Il Lee from the Gyeongsang National University School of Medicine in South Korea evaluated the immune response of mice with experimentally induced rheumatoid arthritis. The researchers looked both in normal mice and those genetically engineered not to produce SIRT1, an enzyme known to regulate aging, cellular stress responses, metabolism and inflammation. The myeloid-specific SIRT1 conditional knockout mice had less severe disease, owing to reduced levels of several immune molecules. In ex-vivo and in vitro, the researchers showed that one type of immune cell, called a dendritic cell, was less likely to mature and drive less inflammatory response when taken from SIRT1-deficient mice. The findings suggest that targeting SIRT1 with drugs could help in the clinical management of rheumatoid arthritis.