Inhibition of membrane RANKL production in osteoblasts mediates curcumin-inhibited osteoclastogenesis.

Curcumin inhibits osteoclastogenesis and mitigates osteoporosis. Our data demonstrated that curcumin decreases membrane-bound RANKL (mRANKL) levels on osteoblasts. Notably, mRANKL exerts a more prominent role in osteoclastogenesis than its soluble counterpart (sRANKL). This study aimed to explore the role of RANKL membrane localization in curcumin-regulated osteoclastogenesis. We primarily investigated the effect of curcumin on mRANKL expression in osteoblasts in vitro and in vivo. Using fluorescence-activated cell sorting (FACS) for RANKL and co-culture experiments of osteoclast precursors (OCPs) with osteoblasts, we further analyzed the association between curcumin's indirect inhibition of osteoclast differentiation and mRANKL production. Finally, we explored the involvement of matrix metalloproteinase 14 (MMP14) in curcumin-mediated regulation of mRANKL levels. The results showed that curcumin significantly reduced mRANKL expression in osteoblasts. Curcumin also abrogated the upregulated RANKL levels in osteoblasts of Tg-hRANKL transgenic mice. Co-culture assays revealed that curcumin exerted the weakest inhibitory effect on osteoclast differentiation when OCPs were co-cultured with mRANKL-negative osteoblasts. Additionally, curcumin increased MMP14 expression in osteoblasts and enhanced the MMP14-RANKL interaction. Importantly, silencing MMP14 in osteoblasts reversed curcumin-inhibited mRANKL levels and osteoclast differentiation. Collectively, our findings indicated that curcumin inhibited mRANKL production in osteoblasts, which contributes to its therapeutic effect on osteoclastic osteoporosis.