Salidroside inhibits osteoclast differentiation based on osteoblast-osteoclast interaction via HIF-1α pathway

Objective: This study aimed to explore the regulatory potential of salidroside (SAL), a primary active compound in Rhodiola rosea L., on the osteoclast differentiation by modulating the hypoxia-inducible factor 1-alpha (HIF-1α) pathway in osteoblasts. Materials and Methods: Luciferase reporter assay and chromatin immunoprecipitation (ChIP) assay were used to validate whether receptor activator of nuclear factor-κB ligand (RANKL) is the downstream target gene of HIF-1α in osteoblasts. Additionally, the study utilized lipopolysaccharide (LPS)-induced mouse osteolysis to investigate the impact of SAL on osteolysis in vivo. Finally, conditioned medium (CM) from SAL-pretreated osteoblasts was used to investigate the paracrine effects of osteoclastogenesis through the HIF-1α pathway. Results: The hypoxic condition-induced overexpression of HIF-1α upregulated RANKL levels by binding to the RANKL promoter and enhancing transcription in osteoblastic cells. In vivo, SAL significantly alleviated bone tissue hypoxia and decreased the expression of HIF-1α through downregulating the expression of RANKL, vascular endothelial growth factor (VEGF), interleukin 6 (IL-6) and angiopoietin-like 4 (ANGPTL4). In the paracrine experiment, conditioned media from SAL-pretreated osteoblasts inhibited differentiation through the HIF-1α/RANKL, VEGF, IL-6, and ANGPTL4 pathways. Conclusion: RANKL emerges as the downstream target gene which is regulated by HIF-1α in osteoblasts. SAL significantly alleviates bone tissue hypoxia and bone loss in LPS-induced osteolysis through the HIF-1α/RANKL, VEGF, IL-6, and ANGPTL4 pathways. SAL inhibits osteoclast differentiation by regulating osteoblast paracrine secretion.