Potential mechanism of transcription factor peroxisome proliferator-activated receptor-gamma coactivator-1 beta on promoting osteoclastogenesis

Abstract

Objective: To investigate the role of transcription factor peroxisome proliferator-activated receptor-gamma coactivator-1 beta (PGC-1β) on osteoclastogenesis and related regulatory mechanism in the mouse monocyte-macrophage cell line (RAW264.7). Methods: PGC-1β expression and location in RAW264.7 cells was detected by immunofluorescence, flow cytometry and western blot analysis with nuclear protein extraction. RAW264.7 cells were transfected with lentivirus for gene silencing or over-expression of PGC-1β and cultured with macrophage colony-stimulating factor and receptor activator for nuclear factor-κB ligand. Cell viability was detected by cell counting kit-8. Cell apoptosis and cell cycle were detected by flow cytometry. Mature osteoclasts and their bone resorption activity were determined by tartrate-resistant acid phosphatase (TRAP) expression and toluidine blue staining. Western blot analysis was performed for detecting dendritic cell-specific transmembrane protein (DC-STAMP), cathepsin K, TRAP and matrix metalloproteinase (MMP)-9 expression, as well as cytoplasmic NF-κB-inducing kinase (NIK) and nuclear RelB. Results: PGC-1β expression was observed in the nuclei of RAW264.7 cells. Down-regulation or overexpression of PGC-1β in RAW264.7 cells did not affect cell viability, apoptosis or cell cycle. Down-regulation of PGC-1β decreased the count of mature osteoclasts (49±21 cells vs. 147±42 cells, P=0.004) and the pit area of bone resorption lacunae (42.11μm(2)±11.30 μm(2) vs. 204.80μm(2)±31.09 μm(2), P<0.001), as well as the expression of cathepsin K, TRAP and MMP-9, but not DC-STAMP. Overexpression of PGC-1β promoted osteoclast differentiation and bone resorption activity, as well as the expression of cathepsin K, TRAP and MMP-9. Down-regulation of PGC-1β suppressed the protein expression of cytoplasmic NIK and nuclear RelB in RAW264.7 cells. Conclusion: PGC-1β can promote the differentiation of RAW264.7 into osteoclasts and improve the bone resorption ability of the cells via activation of NIK/RelB pathway, which might be a promising therapeutic target for osteoporosis.