To observe the effect of hypoxia on osteoclast formation, and to explore the regulatory role of hypoxia inducible factor-2α (HIF-2α).

Osteoclasts were cultured in normal oxygen concentration, 5% O₂ concentration and 1% O₂ concentration, and counted after tartrate-resistant acid phosphatase (TRAP) staining. The expression of HIF-2α in osteoclasts under hypoxia condition was detected by Western blotting. After HIF-2α activity was inhibited by HIF-2α inhibitor PT2385 (5 μmol/L), the expression of genes related to osteoclast function was detected by real-time fluorescence quantitative polymerase chain reaction (RT-qPCR).

TRAP staining showed that bone marrow mononuclear cells (BMM) could induce osteoclasts successfully. The number of osteoclasts in the normal oxygen group was (55.1±8.2), (72.5±10.7) in the 5% O₂ hypoxia group, and (94.7±15.6) in the 1% O₂ hypoxia group, with the difference being statistically significant (F=8.341, P<0.05). The protein expression of HIF-2α in osteoclasts was increased under hypoxic conditions. The expression of HIF-2α in 5% O₂ hypoxic group was 3.1 times higher than that in the normal oxygen group, and that in the 1% O₂ hypoxic group was 6.5 times higher than that in the normal oxygen group, with statistically significant difference (F=21.070, P<0.05). The expression of TRAP, cathepsin K (CK), matrix metalloproteinase-9 (MMP-9), and activated T nuclear factor 1 (NFATC1) genes increased in the 5% O₂ hypoxia group, and PT2385 (5 μmol/L) could counteract the effect of hypoxia, and the difference was statistically significant ( P<0.05).

Hypoxic environment can promote the formation and differentiation of osteoclasts by activating HIF-2α, and blocking HIF-2α can inhibit the bone resorption of osteoclasts, suggesting that HIF2-α may be a therapeutic target for osteoporosis.

Osteoclast; Hypoxia inducible factor-2 α; Bone metabolism