Background: Osteoporosis is a very common skeletal disorder that increases the risk of fractures. However, the treatment of osteoporosis is challenging. Hypoxia-inducible factor-1α (HIF-1α) plays an important role in bone metabolism. Roxadustat is a novel HIF stabilizer, and its effects on bone metabolism remain unknown. This study aimed to investigate the effects of roxadustat on osteoblast differentiation and bone remodeling in an ovariectomized (OVX) rat model. Methods: In vitro, primary mouse calvarial osteoblasts were treated with roxadustat. Alkaline phosphatase (ALP) activity and extracellular matrix mineralization were assessed. The mRNA and protein expression levels of osteogenic markers were detected. The effects of roxadustat on the HIF-1α and Wnt/β-catenin pathways were evaluated. Furthermore, osteoblast differentiation was assessed again after HIF-1α expression knockdown or inhibition of the Wnt/β-catenin pathway. In vivo, roxadustat was administered orally to OVX rats for 12 weeks. Then, bone histomorphometric analysis was performed. The protein expression levels of the osteogenic markers HIF-1α and β-catenin in bone tissue were detected. Results: In vitro, roxadustat significantly increased ALP staining intensity, enhanced matrix mineralization and upregulated the expression of osteogenic markers at the mRNA and protein levels in osteoblasts compared with the control group. Roxadustat activated the HIF-1α and Wnt/β-catenin pathways. HIF-1α knockdown or Wnt/β-catenin pathway inhibition significantly attenuated roxadustat-promoted osteoblast differentiation. In vivo, roxadustat administration improved bone microarchitecture deterioration and alleviated bone loss in OVX rats by promoting bone formation and inhibiting bone resorption. Roxadustat upregulated the protein expression levels of the osteogenic markers, HIF-1α and β-catenin in the bone tissue of OVX rats. Conclusion: Roxadustat promoted osteoblast differentiation and prevented bone loss in OVX rats. The use of roxadustat may be a new promising strategy to treat osteoporosis.

Bone remodeling relies on a balance between osteoclast-mediated resorption and osteoblast-mediated formation. Roxadustat, a hypoxia-inducible factor prolyl hydroxylase inhibitor, promotes osteoblast differentiation but its effects on osteoclasts remain unclear. This study investigated roxadustat’s impact on osteoclast differentiation and function in vitro using primary murine bone marrow-derived mononuclear cells differentiated with M-CSF and RANKL. Cell viability, TRAP staining, bone resorption assays, RNA-seq, flow cytometry, immunofluorescence, Western blot for p27, and rescue experiments with the cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitor abemaciclib were performed. Roxadustat suppressed osteoclast differentiation and resorption without cytotoxicity in a concentration-dependent manner. RNA-seq revealed enrichment of cell cycle pathways; although differentiation was inhibited, roxadustat paradoxically promoted osteoclast precursor proliferation, evidenced by increased Ki67 and decreased p27 expression. The inhibitory effects on osteoclastogenesis and resorption were partially reversed by abemaciclib. Given that terminal differentiation typically requires cell cycle exit, these findings suggest that roxadustat may inhibit osteoclast differentiation at least in part by disrupting this process, promoting precursor proliferation, and downregulating p27. Together with its known anabolic effects on osteoblasts, roxadustat might have dual therapeutic potential for bone disorders with renal anemia, such as osteoporosis in chronic kidney disease.