Controlling hypoxia-inducible factor-2a is critical for maintaining bone homeostasis in mice

Pathological bone loss is caused by an imbalance between bone formation and resorption. The bone microenvironments are hypoxic, and hypoxia-inducible factor (HIF) is known to play notable roles in bone remodeling. However, the relevant functions of HIF-2a are not well understood. Here, we have shown that HIF-2a deficiency in mice enhances bone mass through its effects on the differentiation of osteoblasts and osteoclasts. In vitro analyses revealed that HIF-2a inhibits osteoblast differentiation by targeting Twist2 and stimulates RANKL-induced osteoclastogenesis via regulation of Traf6. In addition, HIF-2a appears to contribute to the crosstalk between osteoblasts and osteoclasts by directly targeting RANKL in osteoprogenitor cells. Experiments performed with osteoblast- and osteoclast-specific conditional knockout mice supported a role of HIF-2a in this crosstalk. HIF-2a deficiency alleviated ovariectomy-induced bone loss in mice, and specific inhibition of HIF-2a with ZINC04179524 significantly blocked RANKL-mediated osteoclastogenesis. Collectively, our results suggest that HIF-2a functions as a catabolic regulator in bone remodeling, which is critical for the maintenance of bone homeostasis.