Punicalin Attenuates Breast Cancer-Associated Osteolysis by Inhibiting the NF-κB Signaling Pathway of Osteoclasts

Background: Breast cancer bone metastasis and osteoporosis are both severe diseases that seriously threaten human health. These diseases are closely associated with osteolytic lesions. And osteoclasts are the key targets of this pathological process. Given the lack of effective preventive or treatment options against these diseases, the exploitation of new pharmacological agents is critically required.Method: We assessed the efficacy of punicalin on receptor activator of nuclear factor-κB ligand (RANKL)-mediated osteoclast formation, F-actin ring formation, gene expression, bone resorption, nuclear factor-κB (NF-κB) as well as on mitogen-activated protein kinase (MAPK) signaling pathways and molecular docking in vitro. The impact of punicalin on breast cancer-induced osteoclastogenesis, breast cancer cell proliferation, and apoptosis were examined. Transwell assays were also performed. Moreover, we evaluated in vivo effects of punicalin in postmenopausal osteoporosis models and breast cancer bone metastasis model by micro-CT scanning and histomorphometry.Results: Punicalin inhibited osteoclast formation, F-actin ring formation, bone resorption, as well as osteoclast-related gene expression by suppressing the NF-κB signaling pathway. In vitro, punicalin also suppressed the breast cancer-induced osteoclastogenesis, and proliferation, migration as well as invasion of MDA-MB-231 cells and dose-dependently promoted their apoptosis. In vivo, punicalin significantly suppressed breast cancer-induced osteolysis, breast cancer-associated bone metastasis, and ovariectomized (OVX)-mediated osteoporosis by repressing osteoclast and breast cancer cell.Conclusion: Punicalin is expected to offer a novel treatment for the prevention of osteolysis diseases, including osteoporosis and breast cancer-associated osteolysis.

BCI Suppresses RANKL-Mediated Osteoclastogenesis and Alleviates Ovariectomy-Induced Bone Loss

Osteoporosis is a common aging-related metabolic disease that mainly occurs in older adults and postmenopausal women. Despite advances in anti-osteoporosis treatment, outcomes remain unsatisfactory due to detrimental side effects. BCI hydrochloride (BCI), a selective dual-specificity phosphatase 6 (DUSP6) inhibitor, is associated with multiple cellular functions, including inhibiting tumor growth and macrophage inflammation; however, its role in regulating osteoclast differentiation remains unknown. Here, we revealed that treatment with BCI attenuated RANKL-mediated osteoclast differentiation in vitro and alleviated ovariectomy-induced osteoporosis without obvious toxicity. Specifically, BCI disrupted F-actin ring formation and bone-resorption activity and decreased osteoclast-specific gene and protein levels in a dose-dependent manner. KEGG pathway analysis, GSEA based on transcriptome sequencing, and western blot results suggested that BCI inhibited RANKL-induced osteoclastogenesis by restraining STAT3 and NF-κB signaling and attenuating NF-κB/p65 interaction with NFATc1. These results revealed that BCI treatment prevented postmenopausal osteoporosis and might represent an effective approach for treating osteoporosis.

Hyperoside Suppresses Osteoclasts Differentiation and Function through Down-Regulating TRAF6/p38 MAPK Signaling Pathway

Background: Osteoporosis (OP) is a systemic metabolic bone disease that the bone resorption exceeds the bone formation,resulting in reduced bone mass, degeneration of the microstructure of bone tissue, and then increased bone fragility and fracture risk. Hyperoside (HP), as a natural product, can promote proliferation and differentiation of osteoblasts and presents a protective effect on ovariectomized (OVX) mice. However, the inhibitory effect of HP on osteoclasts (OCs) and the potential mechanism remains to be elucidated.Methods: In this study, RAW264.7 cells were used to generate OCs induced by RANKL, and HP was applied to the cell model. The effect of HP on OCs differentiation by TRAP-positive cell counting and TRAP activity test; Bone resorption assay and actin ring formation assay were used to verify the effect of HP on OCs function; The expression levels of osteoclast-specific genes and proteins were proved by RT-PCR and Western blotting.Results: HP significantly suppressed RANKL-induced OCs differentiation, function and the mRNAs expression levels of the osteoclast-related genes. Western Blotting results demonstrated that HP reduced the expression level of TNF receptor-associated factor 6 (TRAF6) and inhibited the p38 MAPK signing pathway by reducing the phosphorylation level of p38, which subsequently down-regulated the expression level of c-fos and NFATc1, ultimately, led to a decrease of the osteoclast-specific proteins CTSK and TRAP. In addition, TRAP-positive cell counting and TRAP activity test showed that HP could inhibit the differentiation of OCs; Bone resorption assay indicated that HP could restrain the OCs’ bone resorptive activity. Actin ring formation assay showed HP can cause the shrinkage of osteoclasts and disruption of actin ring structure.Conclusion: These results revealed that HP had an inhibitory effect on OCs by down-regulating TRAF6/p38 MAPK signaling pathway. Therefore, HP could be a promising natural compound for lytic bone diseases.

A novel BRD4 inhibitor suppresses osteoclastogenesis and ovariectomized osteoporosis by blocking RANKL-mediated MAPK and NF-κB pathways

Bromodomain-containing protein 4 (BRD4) has emerged as a promising treatment target for bone-related disorders. (+)-JQ1, a thienotriazolodiazepine compound, has been shown to inhibit pro-osteoclastic activity in a BRD4-dependent approach and impede bone loss caused by ovariectomy (OVX) in vivo. However, clinical trials of (+)-JQ1 are limited because of its poor druggability. In this study, we synthesized a new (+)-JQ1 derivative differing in structure and chirality. One such derivative, (+)-ND, exhibited higher solubility and excellent inhibitory activity against BRD4 compared with its analogue (+)-JQ1. Interestingly, (-)-JQ1 and (-)-ND exhibited low anti-proliferative activity and had no significant inhibitory effect on RANKL-induced osteoclastogenesis as compared with (+)-JQ1 and (+)-ND, suggesting the importance of chirality in the biological activity of compounds. Among these compounds, (+)-ND displayed the most prominent inhibitory effect on RANKL-induced osteoclastogenesis. Moreover, (+)-ND could inhibit osteoclast-specific gene expression, F‐actin ring generation, and bone resorption in vitro and prevent bone loss in OVX mice. Collectively, these findings indicated that (+)-ND represses RANKL‐stimulated osteoclastogenesis and averts OVX-triggered osteoporosis by suppressing MAPK and NF-κB signalling cascades, suggesting that it may be a prospective candidate for osteoporosis treatment.

Sec-O-glucosylhamaudol Inhibits RANKL-induced Osteoclastogenesis Via Repressing 5-LO and AKT/GSK3β Signaling

BackgroundOsteoclast excessive activation was closely related to bone diseases such as osteoporosis and rheumatoid arthritis. Sec-O-glucosylhamaudol (SOG), an active flavonoid compound derived from the root of divaricate Saposhnikovia, was reported to exhibit analgesic, anti-inflammatory and high 5-lipoxygenase (5-LO) inhibitory effects. However, its effect on osteoclastogenesis and bone resorption remained unclear.MethodsOsteoclast formation, bone resorption pit area formation and F-actin ring formation were examined by TRAP staining, modified Vonkonsa staining and immunofluorescence, respectively. RT-Realtime PCR assay and western blot analysis were performed. siRNA transfection was conducted to silence the expression of 5-LO in cells. LPS-induced bone-loss mice model was prepared and the left and right femurs were collected for Micro-CT and histomorphometric analysis, respectively.ResultsSOG markedly attenuated RANKL-induced osteoclastogenesis through decreasing TRAP activity, F-actin ring formation and bone resorption with reduction of mRNA levels of osteoclastogenesis marker genes such as TRAP, CTSK and DC-STAMP. Our results further indicated that SOG markedly reduced the induction of key transcription factors NFATc1 and c-Fos at both mRNA and protein levels during osteoclastogenesis. In addition, SOG treatment did not alter the transient phosphorylation of NF-κB p65 subunit and MAPKs (p38, ERK1/2 and JNK), AKT and GSK3β by RANKL. Interestingly, our results showed that SOG significantly inhibited the phosphorylation of AKT and GSK3β at middle-late stage of osteoclastogenesis, but did not alter calcineurin catalytic subunit PP2B-Aα expression. GSK3β inhibitor SB415286 could partly reverse inhibition of osteoclastogenesis by SOG. 5-LO knockdown at BMMs also markedly reduced RANKL-induced osteoclastogenesis. In consistent with in vitro results，SOG could significantly improve bone destruction in LPS-induced mice model.ConclusionsSOG attenuated formation and function of osteoclast through suppressing AKT-mediated GSK3β inactivation, and 5-LO catalytic activity. Moreover, SOG prevented LPS-induced bone loss in mice through inhibiting osteoclastogenesis. Taken together, this study provided the evidence that SOG may have a potential therapeutic effect on osteoclast-related bone lysis disease.

GNAS Heterozygous Inactivation Differentially Affects Osteoclast-Specific Calcitonin Receptor Bioactivity in a Mouse Model of Albright Hereditary Osteodystrophy Based Upon Parental Inheritance

Albright hereditary osteodystrophy (AHO) is caused by the heterozygous inactivation of GNAS, encoding the α-stimulatory subunit (Gαs) of G protein-coupled receptors. Skeletal manifestations of AHO include adult short stature, brachydactyly and subcutaneous ossifications. AHO patients with maternally-derived GNAS mutations develop pseudohypoparathyroidism type 1A (PHP1A) and are obese with resistance to hormones requiring Gαs (eg., PTH, TSH and GHRH) due to tissue-specific GNAS imprinting. Paternally-derived GNAS mutations cause pseudopseudohypoparathyroidism (PPHP) in which patients have AHO skeletal features but do not develop severe obesity or hormonal resistance. Mouse models have shown loss of Gα s signaling in osteoblasts or osteoclasts leads to osteopenia, and suggest AHO patients would display a reduced bone mineral density (BMD). Interestingly, PHP1A patients have been shown to have normal to increased BMD without any correlation to body mass index or serum PTH measurement. Based on the differences observed clinically and hormonally between PHP1A and PPHP, we hypothesize that there may also be distinctions in overall bone remodeling between these two disorders due to GNAS imprinting. This study addressed whether the heterozygous inactivation of Gnas differentially affects Gα s-receptor bioactivity within osteoclasts (OCs) based upon parental inheritance. Bone Marrow Macrophages (BMMs) were harvested from our laboratory’s AHO mouse model with either maternally-inherited (Gnas+/-m) mutations correlating to PHP1A or paternally-inherited (Gnas+/-p) mutations correlating to PPHP. BMMs were exposed to 10-7M salmon calcitonin (sCT), 10-5M forskolin or PBS for 6 hrs. OC receptor activity was measured by fluorescent microscopy to visualize actin ring morphology and RT-PCR analysis of Gα s-PKA signaling transcripts Crem and Ramp3. Forskolin treatment displayed no significant variations in OC ring morphology or Crem and Ramp3 mRNA expression between Gnas+/-m, Gnas+/-p and WT cultures. Both WT and Gnas+/-p OCs displayed appropriate responses to sCT, as indicated by a significant disruption in actin ring morphology and increased Crem and Ramp3 mRNA expression when compared to vehicle-treated controls. SCT-treated Gnas+/-m OCs, however, displayed only mild disruptions in actin ring morphology, and we observed significant reductions in Ramp3 expression compared to WT as well as reductions in Crem compared to WT and Gnas+/-p. These data suggest evidence of partial calcitonin resistance within Gnas+/-m OCs due to impaired Gα s- signaling. These data correlate with previous clinical observations of calcitonin resistance in PHP1A patients. Because these findings were observed only within Gnas+/-m cultures, future work is warranted to determine whether this impaired receptor activity may be attributed to partial Gnas imprinting within OCs or the myeloid lineage.

Estrogen Decreases Cytoskeletal Organization by Forming an ERα/SHP2/c-Src Complex in Osteoclasts to Protect against Ovariectomy-Induced Bone Loss in Mice

Loss of ovarian function is closely related to estrogen (E2) deficiency, which is responsible for increased osteoclast (OC) differentiation and activity. We aimed to investigate the action mechanism of E2 to decrease bone resorption in OCs to protect from ovariectomy (OVX)-induced bone loss in mice. In vivo, tartrate-resistant acid phosphatase (TRAP) staining in femur and serum carboxy-terminal collagen crosslinks-1 (CTX-1) were analyzed upon E2 injection after OVX in mice. In vitro, OCs were analyzed by TRAP staining, actin ring formation, carboxymethylation, determination of reactive oxygen species (ROS) level, and immunoprecipitation coupled with Western blot. In vivo and in vitro, E2 decreased OC size more dramatically than OC number and Methyl-piperidino-pyrazole hydrate dihydrochloride (MPPD), an estrogen receptor alpha (ERα) antagonist, augmented the OC size. ERα was found in plasma membranes and E2/ERα signaling affected receptor activator of nuclear factor κB ligand (RANKL)-induced actin ring formation by rapidly decreasing a proto-oncogene tyrosine-protein kinase, cellular sarcoma (c-Src) (Y416) phosphorylation in OCs. E2 exposure decreased physical interactions between NADPH oxidase 1 (NOX1) and the oxidized form of c-Src homology 2 (SH2)-containing protein tyrosine phosphatase 2 (SHP2), leading to higher levels of reduced SHP2. ERα formed a complex with the reduced form of SHP2 and c-Src to decrease c-Src activation upon E2 exposure, which blocked a signal for actin ring formation by decreased Vav guanine nucleotide exchange factor 3 (Vav3) (p–Y) and Ras-related C3 botulinum toxin substrate 1 (Rac1) (GTP) activation in OCs. E2/ERα signals consistently inhibited bone resorption in vitro. In conclusion, our study suggests that E2-binding to ERα forms a complex with SHP2/c-Src to attenuate c-Src activation that was induced upon RANKL stimulation in a non-genomic manner, resulting in an impaired actin ring formation and reducing bone resorption.

Reconstitution of contractile actomyosin rings in vesicles

One of the grand challenges of bottom-up synthetic biology is the development of minimal machineries for cell division. The mechanical transformation of large-scale compartments, such as Giant Unilamellar Vesicles (GUVs), requires the geometry-specific coordination of active elements, several orders of magnitude larger than the molecular scale. Of all cytoskeletal structures, large-scale actomyosin rings appear to be the most promising cellular elements to accomplish this task. Here, we have adopted advanced encapsulation methods to study bundled actin filaments in GUVs and compare our results with theoretical modeling. By changing few key parameters, actin polymerization can be differentiated to resemble various types of networks in living cells. Importantly, we find membrane binding to be crucial for the robust condensation into a single actin ring in spherical vesicles, as predicted by theoretical considerations. Upon force generation by ATP-driven myosin motors, these ring-like actin structures contract and locally constrict the vesicle, forming furrow-like deformations. On the other hand, cortex-like actin networks are shown to induce and stabilize deformations from spherical shapes.

Inhibitory Effects of Gold and Silver Nanoparticles on the Differentiation into Osteoclasts In Vitro

Gold nanoparticles (GNPs) have been widely studied to inhibit differentiation into osteoclasts. However, reports of the inhibitory effects of silver nanoparticles (SNPs) during the process of differentiation into osteoclasts are rare. We compared the inhibitory effect of GNPs and SNPs during the process of differentiation into osteoclasts. Bone marrow-derived cells were differentiated into osteoclasts by the receptor activator of the nuclear factor-kappa-Β ligand (RANKL). The inhibitory effect of GNPs or SNPs during the process of differentiation into osteoclasts was investigated using tartrate-resistant acid phosphatase (TRAP) and actin ring staining. The formation of TRAP positive (+) multinuclear cells (MNCs) with the actin ring structure was most inhibited in the SNP group. In addition, the expression of specific genes related to the differentiation into osteoclasts, such as c-Fos, the nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), TRAP, and Cathepsin K (CTSK) were also inhibited in the SNP groups. As a result, the levels related to differentiation into osteoclasts were consistently lower in the SNP groups than in the GNP groups. Our study suggests that SNPs can be a useful material for inhibiting differentiation into osteoclasts and they can be applied to treatments for osteoporosis patients.

The Effect of Alendronate on Osteoclastogenesis in Different Combinations of M-CSF and RANKL Growth Factors

Bisphosphonates (BPs) are compounds resembling the pyrophosphate structure. BPs bind the mineral component of bones. During the bone resorption by osteoclasts, nitrogen-containing BPs are released and internalized, causing an inhibition of the mevalonate pathway. As a consequence, osteoclasts are unable to execute their function. Alendronate (ALN) is a bisphosphonate used to treat osteoporosis. Its administration could be associated with adverse effects. The purpose of this study is to evaluate four different ALN concentrations, ranging from 10−6 to 10−10 M, in the presence of different combinations of M-CSF and RANKL, to find out the effect of low ALN concentrations on osteoclastogenesis using rat and human peripheral blood mononuclear cells. The cytotoxic effect of ALN was evaluated based on metabolic activity and DNA concentration measurement. The alteration in osteoclastogenesis was assessed by the activity of carbonic anhydrase II (CA II), tartrate-resistant acid phosphatase staining, and actin ring formation. The ALN concentration of 10−6 M was cytotoxic. Low ALN concentrations of 10−8 and 10−10 M promoted proliferation, osteoclast-like cell formation, and CA II activity. The results indicated the induction of osteoclastogenesis with low ALN concentrations. However, when high doses of ALN were administered, their cytotoxic effect was demonstrated.