THU0075 Tacrolimus Regulates the Expression of Endoplasmic Reticulum Stress-Mediated Osteoclastogenesis and Inflammation in Vitro and in Collagen-Induced Arthritis Mouse Model

Background Tacrolimus is a T cell specific, anti-inflammatory agent that has been used as a therapeutic agent for rheumatoid arthritis (RA). IL-1b- and thapsigargin (TG)-induced endoplasmic reticulum (ER) stress modulates the receptor activator of nuclear factor kappa-B ligand (RANKL)-mediated osteoclastogenesis. Objectives This study was aimed at defining the effect of tacrolimus on endoplasmic reticulum stress-mediated osteoclastogenesis and inflammation and to elucidate the underlying mechanisms. Methods Bone marrow cells (BMCs) were obtained from 5-week-old male ICR mice and cultured to differentiate them into osteoclasts with M-CSF and RANKL in the presence or absence of IL-1β, TG, or TAC. The formation of osteoclasts was evaluated by tartrate-resistant acid phosphatase (TRAP) staining and resorption pit assay with dentine slice. Collagen-induced arthritis (CIA) was induced by immunization of female Lewis rats with an emulsion of bovine type II collagen and incomplete Freund9s adjuvant. Lesions of bone and cartilage were assessed on the basis of histological changes in the knee joint and radiographic analysis of the hind paw. Tacrolimus at doses of 3.2 mg/kg or its placebo formulation was orally administered to rats for 28 days from the day after immunization. We examined the histopathological changes of osteolysis and the expression of specific ER stress-mediated inflammatory signaling pathway biomarkers (IRE1α, GRP78/Bip, c-Fos, and NF-κB). In addition, pro-inflammatory cytokines and osteoclastogenic molecules (RANKL, and M-CSF) were assessed in the knee and ankle joints in the CIA mouse model. Results In vitro, IL-1b- and thapsigargin (TG)-induced endoplasmic reticulum stress modulates the receptor activator of nuclear factor kappa-B ligand (RANKL)-mediated osteoclastogenesis. In the mouse model, tacrolimus administration resulted in a dramatic amelioration of osteolysis and significant reduction in ER stress intensity. Simultaneously, tacrolimus lessened inflammatory cell infiltration, reduced the capability of osteoclastogenesis, and reduced the inflammatory response by reducing the levels of IRE1α, GRP78/Bip, c-Fos, and NF-κB. Conclusions These findings suggest that tacrolimus has the potential to inhibit the progression of joint damage by inhibiting endoplasmic reticulum stress as well as anti-inflammatory effects in established RA. Disclosure of Interest None declared