Background
To maintain the bone strength and functions, the balance between bone resorption and bone formation has to be tightly regulated. However, under certain pathological conditions, including osteoporosis and rheumatoid arthritis, the equilibrium gets disrupted, resulting in a severe bone loss. Recent studies have shown that signaling molecules involved in the unfolded protein response (UPR) are potentially involved in the coupling of bone resorption and bone formation [1–3]. In the present study, we investigated the roles of UPR mediator, the IRE1α-XBP1 pathway in osteoblast differentiation.