Abstract: Objective: To investigate the role of inositol demanding enzyme 1α (IRE1α) pathway in osteoclast differentiation. Methods: Mouse monocyte macrophage line RAW264.7 was induced to differentiate into osteoclasts by treating it with macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-B ligand (RANKL). Western blot and real-time fluorescence quantitative polymerase chain reaction (qRT-PCR) were used to detect the expression levels of osteoclast differentiation related genes and proteins, as well as the expression of the IRE1α pathway. RAW264.7 was treated with IRE1α RNase inhibitor 4μ8c, and its effect on cell proliferation was detected by CCK-8 assay. During the induction of osteoclast differentiation, 4μ8c was used to treat the cells. The effect of 4μ8c on osteoclast formation was evaluated by tartrate resistant acid phosphatase (TRAP) staining, and the expression levels of osteoclast differentiation related proteins and IRE1α pathway proteins were detected by Western blot. RAW264.7 was treated with 4μ8c and stimulated with bacterial lipopolysaccharides (LPS) to simulate an inflammatory environment. qRT-PCR was used to detect the expression of inflammatory factors related to osteoclast differentiation. Results: The expression of IRE1α pathway increased during osteoclast differentiation, and 4μ8c not only significantly inhibited the proliferation of osteoclast precursor cells, but also inhibited osteoclast formation, and downregulated the protein levels of osteoclast differentiation related factors: nuclear factor of activated T-cells (NFATc1), matrix metalloproteinase-9 (MMP-9), and cathepsin K (CTSK). Conclusion: The IRE1α pathway is activated during osteoclast differentiation. Inhibiting the IRE1α pathway not only inhibits the formation and proliferation of osteoclasts, but also downregulates the expression of osteoclast marker proteins and pro-inflammatory factors related to osteoclast differentiation.

Key words: IRE1α, osteoclasts, periodontitis