Abstract
TNFα-induced adipose-related protein (TIARP) is a six-transmembrane protein expressed on macrophages, neutrophils and synoviocytes. We reported recently that mice deficient in TIARP (TIARP-/-) spontaneously develop arthritis and are highly susceptible to collagen-induced arthritis (CIA) with enhanced interleukin (IL)-6 production. However, the effects of TIARP on neutrophils and fibroblast-like synoviocytes (FLS) have not been elucidated. We analyzed the roles of TIARP in K/BxN serum transfer model using TIARP-/- mice. Arthritis in TIARP-/- mice transferred with K/BxN serum was significantly exacerbated compared with WT mice. We characterized the differences in neutrophils between wild-type (WT) and TIARP-/- mice by DNA microarray. Overexpression of CXCR1 and CXCR2 was noted in TIARP-/- neutrophils. Neutrophils of TIARP-/- mice showed strong migration activity, which was markedly facilitated by CXCL2 in vitro and in vivo. Moreover, enhanced production of CXCL2 and IL-6 and cell proliferation was noted in TIARP-/- TNFα-stimulated FLS. Blockade of IL-6R significantly attenuated serum-transferred TIARP-/- arthritis with diminished neutrophil recruitment in joints. Our findings suggested that TIARP independently down-regulated CXCL2 and IL-6 production by FLS, and the expression of chemokine receptors (CXCR1 and CXCR2) in neutrophils, with resultant reduction of neutrophil migration into arthritic joints.