Calcineurin-binding protein 1 (Cabin1) regulates calcineurin phosphatase activity as well as the activation, apoptosis, and inflammatory responses of fibroblast-like synoviocytes (FLSs), which actively participate in the chronic inflammatory responses in rheumatoid arthritis (RA). However, the mechanism of action of Cabin1 in FLS apoptosis is not clear. The aim of this study was to define the regulatory role of Cabin1 in FLSs of mice with collagen-induced arthritis (CIA). Transgenic mice overexpressing human Cabin1 in joint tissues, under the control of a type II collagen promoter, were generated. hCabin1 expression in joints and FLSs was determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis. The expression of cytokines, matrix metalloproteinases (MMPs), and apoptosis-related genes in FLSs was determined by enzyme- linked immunosorbent assay, gelatin zymography, and RT-PCR, respectively. Joints were histologically examined after H&E and TRAP staining. hCabin1-transgenic CIA mice had less severe arthritis than wild-type CIA mice, based on hind paw thickness and histology. This was accompanied by significantly enhanced apoptosis in transgenic mice, evidenced by significantly more TUNEL-positive cells in synovial tissues. The expression of inflammatory cytokines and MMPs was reduced, and the transgenic CIA mice exhibited decreased Akt activation and increased expression of p53, caspase-3, caspase-9, and Bax. hCabin1 plays a critical role in promoting apoptosis of FLSs and in attenuating inflammation and the destruction of cartilage and bone in RA. These findings help elucidate the pathogenic mechanisms of RA and suggest that Cabin1 is a potential target for RA treatment.

• Jun Koo Yi(School of Life Science and Biotechnology, Kyungpook National University, Daegu, Korea)
• Zae Young Ryoo(School of Life Science and Biotechnology, Kyungpook National University, Daegu, Korea)