Activation of osteoclastogenesis at the bone site in rheumatoid arthritis (RA) is well established. The mechanisms by which circulating osteoclast precursors contribute are still unclear. Peroxisome proliferator-activated receptor γ coactivator 1β (PGC-1β) is implicated in transcriptional regulation of osteoclastogenesis in mouse models. This study was undertaken to investigate the contribution of PGC-1β to circulating osteoclast precursors and its link to bone destruction in RA.
PGC-1β expression in RA peripheral blood CD14+ monocytes was increased and showed correlation with joint destruction shown on radiographs. Cells from RA patients or healthy controls were transfected with a lentivirus vector for PGC-1β gene silencing or overexpression and cultured with macrophage colony-stimulating factor and RANKL. Bone resorption activity, bone-degrading enzymes, and signaling molecules were measured in these mature osteoclasts.
Increased nuclear accumulation of PGC-1β was observed in RA peripheral blood CD14+ monocytes, and these cells had stronger osteoclastogenesis than in healthy controls. PGC-1β protein expression was positively correlated with radiographic joint destruction (r = 0.396-0.413; all P < 0.05). PGC-1β knockdown suppressed (51-82% reduction) the expression of cathepsin K, tartrate-resistant acid phosphatase (TRAP), and matrix metalloproteinase 9 (MMP-9), as well as osteoclast differentiation and bone resorption activity. Conversely, PGC-1β overexpression increased these markers (by 1.5-1.8-fold) and osteoclastogenesis. VIVIT, an inhibitor of NFATc1 activation, inhibited the effect of overexpressed PGC-1β by reducing cathepsin K, TRAP, and MMP-9 expression. Chromatin immunoprecipitation assay and dual-luciferase reporter gene assay showed PGC-1β bound to NFATc1 promoter, leading to transcriptional activation.
Activation of the PGC-1β/NFATc1 pathway in circulating osteoclast precursors was associated with bone destruction in RA. This may represent a new treatment target.