Cyanidin-3-glucoside (C3G) is one of the major components of anthocyanin, a water-soluble phytochemical. Recent studies demonstrated the chemopreventive and chemotherapeutic activities of C3G in various conditions, including cancer, although the precise effects of C3G on osteoclast and osteoblast differentiation remain unclear. Here, we investigated the role of C3G in the differentiation of bone-associated cells and its underlying mechanism. C3G inhibited receptor activator of nuclear factor kappa-B ligand (RANKL)-mediated osteoclast differentiation and formation in a dose-dependent manner and downregulated the expression of osteoclast differentiation marker genes. Pretreatment with C3G considerably reduced the induction of extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 mitogen-activated kinases activation by RANKL in osteoclast precursor cells. Furthermore, C3G dramatically inhibited the expression of c-Fos and nuclear factor of activated T-cells, cytoplasmic 1, which are important transcription factors for osteoclast differentiation and activation. The formation of osteoclasts in coculture of bone marrow cells and calvaria-derived osteoblasts was also inhibited by C3G treatment, although the expression of macrophage colony-stimulating factor and RANKL (master factors for osteoclast differentiation and formation) and osteoprotegerin (a decoy receptor for RANKL) on osteoblasts was unaffected. The inhibitory effect of C3G on osteoclastogenesis is therefore targeted specifically to osteoclasts but not osteoblasts. Moreover, analysis of the expression levels of osteoblast differentiation marker genes and alizarin red staining showed that osteoblast differentiation and matrix formation increased after C3G treatment. Taken together, these results strongly suggest that C3G has a dual role in bone metabolism, as an effective inhibitor of osteoclast differentiation but also as an activator of osteoblast differentiation. Therefore, C3G may be used as a potent preventive or therapeutic agent for bone-related diseases, such as osteoporosis, rheumatoid arthritis, and periodontitis.

Lysosomal Ca emerges as a critical component of receptor-evoked Ca signaling and plays a crucial role in many lysosomal and physiological functions. Lysosomal Ca release is mediated by the transient receptor potential (TRP) family member TRPML1, mutations that cause the lysosomal storage disease mucolipidosis type 4. Lysosomes play a key role in osteoclast function. However, nothing is known about the role of lysosomal Ca signaling in osteoclastogenesis and bone metabolism. In this study, we addressed this knowledge gap by studying the role of lysosomal Ca signaling in osteoclastogenesis, osteoclast and osteoblast functions, and bone homeostasis in vivo. We manipulated lysosomal Ca signaling by acute knockdown of TRPML1, deletion of TRPML1 in mice, pharmacological inhibition of lysosomal Ca influx, and depletion of lysosomal Ca storage using the TRPML agonist ML-SA1. We found that knockdown and deletion of TRPML1, although it did not have an apparent effect on osteoblast differentiation and bone formation, markedly attenuated osteoclast function, RANKL-induced cytosolic Ca oscillations, inhibited activation of NFATc1 and osteoclastogenesis-controlling genes, suppressed the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells (MNCs), and markedly reduced the differentiation of bone marrow-derived macrophages into osteoclasts. Moreover, deletion of TRPML1 resulted in enlarged lysosomes, inhibition of lysosomal secretion, and attenuated the resorptive activity of mature osteoclasts. Notably, depletion of lysosomal Ca with ML-SA1 similarly abrogated RANKL-induced Ca oscillations and MNC formation. Deletion of TRPML1 in mice reduced the TRAP-positive bone surfaces and impaired bone remodeling, resulting in prominent osteopetrosis. These findings demonstrate the essential role of lysosomal Ca signaling in osteoclast differentiation and mature osteoclast function, which play key roles in bone homeostasis. © 2016 American Society for Bone and Mineral Research.

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Puerariae radix, the dried root of Pueraria lobate Ohwi, is known to prevent bone loss in ovariectomized mice; however, the precise molecular mechanisms are not understood. In this study, we investigated the effects and underlying mechanisms of action of Puerariae radix extract (PRE) on receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis. PRE dose-dependently inhibited osteoclast differentiation and formation, decreased the bone-resorbing activity of osteoclasts, and downregulated the expression of osteoclast differentiation marker genes. The expression of osteoclastogenic factors produced by PRE-treated osteoblasts such as RANKL, macrophage colony-stimulating factor (M-CSF), and osteoprotegerin (OPG) was comparable to that of untreated (control) cells. However, the formation of osteoclasts via bone marrow cell and calvaria-derived osteoblast co-cultures was suppressed by PRE treatment. Therefore, the inhibitory effects of PRE on osteoclastogenesis clearly targeted osteoclasts, but not osteoblasts. PRE treatment considerably reduced RANKL-induced mitogen-activated protein kinases (MAPKs) activity, especially c-Jun N-terminal kinase, in osteoclast precursor cells. In addition, PRE markedly suppressed cAMP response element-binding protein (CREB) activation and the induction of peroxisome proliferator-activated receptor gamma coactivator 1β (PGC1β), which stimulate osteoclastogenesis - an effect that was not observed for puerarin and 17-β estradiol. Finally, PRE treatment significantly repressed the expression of c-Fos and the nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), which is a master transcription factor for osteoclastogenesis in vitro and in vivo. Overall, these results strongly suggest that PRE is an effective inhibitor of RANKL-induced osteoclastogenesis and may be a potent therapeutic agent for bone-related diseases such as osteoporosis, rheumatoid arthritis, and periodontitis.

BackgroundSophorae Flos (SF) is a composite of flowers and buds of Styphnolobium japonicum (L.) Schott and has been used in traditional Korean and Chinese medicine for the treatment of hemostasis and inflammation. Previous studies reported that SF possesses anti-obesity properties, as well as anti-allergic, anti-proliferative, and anti-inflammatory activities. However, the effect of SF in bone resorption has not been studies. In this study, we examined the potential of SF extract (SFE) to inhibit receptor activator of NF-κB ligand (RANKL) -induced osteoclast differentiation in cultured mouse-derived bone marrow macrophages (BMMs).MethodsBMMs, that act as osteoclast precursors, were cultured with M-CSF (50 ng/ml) and RANKL (100 ng/ml) for 4 days to generate osteoclasts. Osteoclast differentiation was measured by tartrate-resistant acidic phosphatase (TRAP) staining and the TRAP solution assay. Osteoclast differentiation marker genes were analyzed by the quantitative real-time polymerase chain reaction analysis. RANKLs signaling pathways were confirmed through western blotting.ResultsSFE significantly decreased osteoclast differentiation in a dose-dependent manner. SFE inhibited RANKL-induced osteoclastogenesis by suppressing NF-κB activation. By contrast, SFE did not affect phospholipase C gamma 2 or subsequent cAMP response element binding activation. SFE inhibited the RANKL-induced expression of nuclear factor of activated T cells c1 (NFATc1).ConclusionsSFE attenuated the RANKL-mediated induction of NF-κB through inhibition of IκBα phosphorylation, which contributed to inhibiting of RANKL-induced osteoclast differentiation through downregulation of NFATc1.