OA-4 Inhibits Osteoclast Formation and Bone Resorption via Suppressing RANKL Induced P38 Signaling Pathway

Circular RNA atlas in osteoclast differentiation with and without alendronate treatment

BACKGROUND

Alendronate (AL) is the most widely used bisphosphonate in the treatment of osteoporosis (OP). However, the role of circular RNAs (circRNAs) in the treatment of OP with AL remains unclear.

METHODS

In this study, we showed that osteoclast (OC) precursors (OPCSs) could be induced into OCs with macrophage colony-stimulating factor (MCSF) and receptor activator of nuclear factor-κB ligand (RANKL) treatment. Subsequently, the OCs were treated with AL. OC differentiation-related biomarkers including RANK, tartrate-resistant acid phosphatase (TRAP), and cathepsin K (CTSK) were analyzed with TRAP staining, quantitative real-time (qPCR), and western blotting. Differentially expressed circRNAs (DECs) were identified among the OPCS, OC, and OC + AL groups. In addition, the expression levels of 10 DECs related to OC differentiation were verified by qPCR.

RESULTS

TRAP staining showed that MCSF and RANKL treatment effectively induced OPCSs to differentiate into OCs. In addition, qPCR and western blot analysis revealed that the three biomarkers of OC (RANK, TRAP, and CTSK) were expressed significantly more in the OC group than those in the OPCS group. In contrast, the mRNA and protein expression levels of these three biomarkers decreased significantly in OCs treated with AL compared with those non-treated OCs. GO analysis of the DECs in the OPCS group vs. the OC group revealed that their functions were mainly related to cell, cell part, binding, and single-organism terms. KEGG analysis of the top 20 DECs in a comparison between the OPCS and OC groups showed that genes involved in mitogen-activated protein kinase signaling were the most common. Results of functional analyses of DECs in an OC vs. OC + AL comparison were similar to those in the OPCS vs. OC comparison. Finally, qPCR showed that, in the OC + AL vs. OC group comparison, the expression levels of seven and three DECs significantly decreased and increased, respectively.

CONCLUSIONS

Having successfully induced OPCSs to differentiate into OCs, we showed that AL suppresses the differentiation of OPCS into OC and that 10 DECs were involved in the regulation of this process. This indicates that these DECs might be important to the treatment of OP.

Hesperetin Prevents Bone Resorption by Inhibiting RANKL-Induced Osteoclastogenesis and Jnk Mediated Irf-3/c-Jun Activation

Bone homeostasis and resorption is regulated by the proper activation of osteoclasts, whose stimulation largely depends on the receptor activator of nuclear factor κB ligand (RANKL)-RANK signaling. Herein, for the first time, we showed that interferon regulatory factor (Irf)-3 was intimately involved in RANKL-induced osteoclast formation. In addition, hesperetin (Hes) derived from citrus fruit could inhibit RANKL-induced osteoclast differentiation and maturation among three types of osteoclast precursors with inhibited formation of F-actin rings and resorption pits on bone slices. More importantly, by using SP600125, a selective Jnk inhibitor, we showed that Hes was able to significantly attenuate the Jnk downstream expression of Irf-3 and c-Jun, thereby inactivating NF-κB/MAPK signaling and transcriptional factor NFATc-1, leading to suppression of osteoclast-specific genes, which resulted in impaired osteoclastogenesis and functionality. An ovariectomized (OVX) osteoporosis mouse model demonstrated that Hes could increase trabecular bone volume fractions (BV/TV), trabecular thickness, and trabecular number, whereas it decreased trabecular separation in OVX mice with well-preserved trabecular bone architecture and decreased levels of TRAP-positive osteoclasts. This is further evidenced by the diminished serum expression of bone resorption marker CTX and enhanced production of osteoblastic ALP in vivo. Taken together, these results suggested that Hes could inhibit Jnk-mediated Irf-3/c-Jun activation, thus attenuating RANKL-induced osteoclast formation and function both in vitro and in vivo.

Flavopiridol Protects Bone Tissue by Attenuating RANKL Induced Osteoclast Formation

Bone resorption and homeostasis is carried out by osteoclasts, whose differentiation and activity are regulated by the RANK/RANKL axis. Our previous studies using a mouse model of joint injury show that joint trauma induces local inflammation followed by bone remodeling. The transcription factor cyclin-dependent kinase 9 (CDK9) is the major regulator of inflammation, as CDK9 inhibitor flavopiridol effectively suppress injury-induced inflammatory response. The objective of this study was to investigate the underlying mechanism through which flavopiridol regulates bone resorption. The effects of CDK9 inhibition, by the specific-inhibitor flavopiridol, on bone resorption were determined in vivo using two distinct and clinically relevant bone remodeling models. The first model involved titanium particle-induced acute osteolysis, and the second model was ovariectomy-induced chronic osteoporosis. The effects and mechanism of CDK9 inhibition on osteoclastogenesis were examined using in vitro culture of bone marrow macrophages (BMMs). Our results indicated that flavopiridol potently suppressed bone resorption in both in vivo bone-remodeling models. In addition, CDK9 inhibition suppressed in vitro osteoclastogenesis of BMM and reduced their expression of osteoclast-specific genes. Finally, we determined that flavopiridol suppressed RANKL signaling pathway via inhibition of p65 phosphorylation and nuclear translocation of NF-κB. Summary, CDK9 is a potential therapeutic target to prevent osteolysis and osteoporosis by flavopiridol treatment.

Kaempferide Prevents Titanium Particle Induced Osteolysis by Suppressing JNK Activation during Osteoclast Formation

Kaempferide (KF) is an O-methylated flavonol, a natural plant extract, which is often found in Kaempferia galanga. It has a variety of effects including anti-carcinogenic, anti-inflammatory, anti-oxidant, anti-bacterial and anti-viral properties. In this study, we aimed to investigate whether KF effectively inhibits titanium particle induced calvarial bone loss via down regulation of the JNK signaling pathway. In the mice with titanium particle induced calvarial osteolysis, the Low dose of KF mildly reduced the resorption pits while in the high dose group, fewer scattered pits were observed on the surface of calvarium. Histological examination showed fewer osteoclasts formation in the KF group. In mouse bone marrow macrophages (BMMs) and RAW264.7 cells, KF significantly inhibited the osteoclast formation and bone resorption at 12.5 μM. However, KF does not affect the mature osteoclast F-actin ring formation. But when being co-treated with KF and anisomycin, BMMs differentiated into mature osteoclasts. At the molecular levels, the JNK phosphorylation was inhibited and the osteoclastogenesis-related specific gene expression including V-ATPase d2, TRAP, calcitonin receptor (CTR), c-Fos and NFATc1 was markedly suppressed. In conclusion, these results indicated that KF is a promising agent in the treatment of osteoclast-related diseases.

Lithium chloride inhibits titanium particle-induced osteoclastogenesis by inhibiting the NF-κB pathway

Osteoclast over-activation and inflammation responses promote peri-implant osteolysis (PIO), which is the leading cause of aseptic artificial joint loosening. We examined the effect of lithium chloride (LiCl) on wear debris-induced osteoclastogenesis and inflammation. Fifty-Six C57BL/6J male mice were randomly distributed into four groups: sham control (sham, treated with phosphate buffered saline [PBS]), vehicle (treated with titanium/PBS), low-LiCl (L-LiCl, titanium: 50 mg/kg LiCl) and high-LiCl (H-LiCl, titanium: 200 mg/kg LiCl). After 14 days, mouse calvaria were harvested for micro-computed tomography and histomorphological and molecular analyses. Bone marrow-derived macrophages (BMMs) were extracted to examine osteoclast differentiation, and the RAW264.7 cell line was used to investigate osteoclastogenesis mechanisms. LiCl reduced the number of osteoclasts, debris-induced osteolysis, and the expression of inflammatory factors, thereby preventing bone loss in vivo. In vitro, LiCl inhibited osteoclastogenesis and osteoclastic bone resorption by inhibiting the RANKL-induced NF-κB signaling pathway. LiCl's activation of the canonical Wnt/β-catenin signaling pathway was not associated with LiCl's inhibition of osteoclastogenesis. These results suggest that LiCl may be an effective agent for treatment of osteolytic diseases caused by chronic inflammation and over-activation of osteoclasts.

Effects of Fluoride on the Expression of p38MAPK Signaling Pathway-Related Genes and Proteins in Spleen Lymphocytes of Mice

This study investigated the effects of sodium fluoride on the expression of p38MAPK signaling pathway-related genes and proteins in the spleen lymphocytes of mice, revealing the mechanism of the toxicity of fluoride to the immune system. The spleen lymphocytes, isolated from mice consuming different NaF doses (0, 50, 100, and 150 mg/L) for 60 days, were cultured in medium with bacteria lipopolysaccharide, and the cells' proliferation ability was analyzed through MTT; real-time PCR detected the change of MLK3/MKK6/p38MAPK/MSK1/ATF1 on mRNA, and the difference of protein expression of MKK6/p38MAPK were detected through the Western blotting. The results suggested that the proliferation ability of spleen lymphocytes isolated from mice consuming different NaF doses is lower, and the expression of genes and proteins of MKK6/p38MAPK showed a decreasing trend. These results demonstrate that fluoride can suppress the activation of p38MAPK pathway in mice spleen lymphocytes and further influences the function of the immune system.

Regulation of expression level of fms-like tyrosine kinase-4 is related to osteoclast differentiation

INTRODUCTION

The aim of this study is to determine whether regulation of the expression level of fms-like tyrosine kinase-4 (Flt-4) is related to osteoclast differentiation.

MATERIAL AND METHODS

Osteoclast formation and differentiation of mouse bone marrow cells and RAW264.7 cells were performed. To induce osteoclast differentiation, RANKL (50 ng/ml) with or without vascular endothelial growth factor-C (VEGF-C) and vascular endothelial growth factor-D (VEGF-D) was added to mouse bone marrow cells and RAW264.7 cells. Then cells were examined under a microscope. TRAP-positive cells with 3 nuclei or more were considered as osteoclasts and counted. The Flt-4 gene was knocked down by transfection of siRNAs against Flt-4. Immunoblot analyses were performed.

RESULTS

The osteoclast formation assay indicated that VEGF-C resulted in 500 or 450 vs. 100 (p < 0.05) of osteoclasts in mouse bone marrow cells and RAW264.7 cells, respectively. Vascular endothelial growth factor-D resulted in about 600 or 630 vs. 100 (p < 0.05) of osteoclasts for both mouse bone marrow cells and RAW264.7 cells. The knock-down of Flt-4 expression abolished the induction by VEGF-C or VEGF-D, resulting in induction similar to that of the negative control PBS.

CONCLUSIONS

Both VEGF-C and VEGF-D can induce osteoclast differentiation in the presence of the receptor activator of nuclear factor κB ligand. Down-regulation of expression level of Flt-4 protein abolishes osteoclast differentiation induced by VEGF-C or VEGF-D.

Silver nanoparticle-loaded hydroxyapatite coating: structure, antibacterial properties, and capacity for osteogenic induction in vitro

AgNP-HAC has the potential to be used on the surfaces of orthopedic and dental implants for infection prophylaxis.

miR-218 is involved in the negative regulation of osteoclastogenesis and bone resorption by partial suppression of p38MAPK-c-Fos-NFATc1 signaling: Potential role for osteopenic diseases

The increased osteoclastic activity accounts for pathological bone loss in diseases including osteoporosis. MicroRNAs are widely accepted to be involved in the regulation of osteopenic diseases. Recently, the low expression of miR-218 was demonstrated in CD14(+) peripheral blood mononuclear cells (PBMCs) from patients with postmenopausal osteoporosis. However, its role and the underlying mechanism in osteoporosis are still undefined. Here, an obvious decrease in miR-218 expression was observed during osteoclastogenesis under receptor activator of nuclear factor κB ligand (RANKL) stimulation, in both osteoclast precursors of bone marrow macrophages (BMMs) and RAW 264.7. Further analysis confirmed that overexpression of miR-218 obviously attenuated the formation of multinuclear mature osteoclasts, concomitant with the decrease in Trap and Cathepsin K levels, both the master regulators of osteoclastogenesis. Moreover, miR-218 up-regulation dramatically inhibited osteoclast precursor migration, actin ring formation and bone resorption. Mechanism assay demonstrated that miR-218 overexpression attenuated the expression of p38MAPK, c-Fos and NFATc1 signaling molecules. Following preconditioning with P79350, an agonist of p38MAPK, the inhibitor effect of miR-218 on osteoclastogenesis and bone-resorbing activity was strikingly ameliorated. Together, this study revealed a crucial role of miR-218 as a negative regulator for osteoclastogenesis and bone resorption by suppressing the p38MAPK-c-Fos-NFATc1 pathway. Accordingly, this research will provide a promising therapeutic agent against osteopenic diseases including osteoporosis.

The prevention of titanium-particle-induced osteolysis by OA-14 through the suppression of the p38 signaling pathway and inhibition of osteoclastogenesis

Wear-particle-induced osteolysis leads to prosthesis loosening, which is one of the most common causes of joint-implant failure, a problem that must be fixed using revision surgery. Thus, a potential treatment for prosthetic loosening is focused on inhibiting osteoclastic bone resorption, which prevents wear-particle-induced osteolysis. In this study, we synthesized a compound named OA-14 (N-(3- (dodecylcarbamoyl)phenyl)-1H-indole-2-carboxamide) and examined how OA-14 affects titanium (Ti)-particle-induced osteolysis and osteoclastogenesis. We report that OA-14 treatment protected against Ti-particle-induced osteolysis in a mouse calvarial model. Interestingly, the number of tartrate-resistant acid phosphatase-positive osteoclasts decreased after treatment with OA-14 in vivo, which suggested that OA-14 inhibits osteoclast formation. To test this hypothesis, we conducted in vitro studies, and our results revealed that OA-14 markedly diminished osteoclast differentiation and osteoclast-specific gene expression in a dose- and time-dependent manner. Moreover, OA-14 suppressed osteoclastic bone resorption and F-actin ring formation. Furthermore, we determined that OA-14 inhibited osteoclastogenesis by specifically blocking the p38-Mitf-c-fos-NFATc1 signaling cascade induced by RANKL (ligand of receptor activator of nuclear factor κB). Collectively, our results suggest that the compound OA-14 can be safely used for treating particle-induced peri-implant osteolysis and other diseases caused by excessive osteoclast formation and function.