Accumulation of hyaluronic acid in stromal cells modulates osteoclast formation by regulation of receptor activator of nuclear factor kappa-B ligand expression

Abstract Hyaluronic acid (HA) has a pivotal role in bone and cartilage metabolism. In this study, we investigated the effect and underlying mechanisms of HA accumulation on the expression of receptor activator of nuclear factor kappa-B ligand (RANKL) induced by 1α,25(OH) 2 D 3 and dexamethasone in stromal cells, which support osteoclastogenesis. Degradation of HA by hyaluronidase (HA'ase) treatment enhanced the expression of RANKL in ST2 cells stimulated with 1α,25(OH) 2 D 3 and dexamethasone. Down-regulation of hyaluronan synthase 2 (HAS2) expression by siRNA also stimulated RANKL expression induced by 1α,25(OH) 2 D 3 and dexamethasone. Results from a cell co-culture system with bone marrow cell showed that 1α,25(OH) 2 D 3 and dexamethasone-induced RANKL expression in HA'ase treated- and HAS2 siRNA transfected-ST2 cells was down-regulated by treatment of cells with high molecular weight HA. In contrast, transforming growth factor-β1 (TGF-β1), which stimulates HAS2 expression and HA synthesis, down-regulated RANKL expression induced by 1α,25(OH) 2 D 3 and dexamethasone. Interestingly, knockdown of has2 gene enhanced the expression of vitamin D receptor (VDR) and phosphorylation of signal transducers and activator of transcription 3 (STAT3) in ST2 cells stimulated by 1α,25(OH) 2 D 3 and dexamethasone. These results indicate that accumulation of HA in bone marrow cells may affect RANKL-mediated osteoclast-supporting activity via regulation of VDR and STAT3 signaling pathways.