Propofol promotes osteoclastic bone resorption by increasing DC-STAMP expression

Background

Propofol is an intravenous anesthetic which has antioxidant effects due to its similarity in molecular structure to α-tocopherol. It has been reported that α-tocopherol increases osteoclast fusion and bone resorption. Here, we investigated the effects of propofol on signaling pathways of osteoclastogenic gene expression, as well as osteoclastogenesis and bone resorption using bone marrow-derived macrophages (BMMs).

Methods

BMMs were cultured with macrophage colony-stimulating factor (M-CSF) alone or M-CSF plus receptor activator of nuclear factor kappa B ligand (RANKL) in the presence of propofol (0-50 µM) for 4 days. Mature osteoclasts were stained for tartrate-resistant acid phosphatase (TRAP) and the numbers of TRAP-positive multinucleated osteoclasts were counted. To examine the resorption activities of osteoclasts, a bone resorption assay was performed. To identify the mechanism of action of propofol on the formation of multinucleated osteoclasts, we focused on dendritic cell-specific transmembrane protein (DC-STAMP), a protein essential for pre-osteoclastic cell fusion.

Results

Propofol increased the formation of TRAP-positive multinucleated osteoclasts. In addition, the bone resorption assay revealed that propofol increased the bone resorption area on dentin discs. The mRNA expression of DC-STAMP was upregulated most strongly in the presence of both RANKL and propofol. However, SB203580, a p38 inhibitor, significantly suppressed the propofol/RANKL-induced increase in mRNA expression of DC-STAMP.

Conclusion

We have demonstrated that propofol enhances osteoclast differentiation and maturation, and subsequently increases bone resorption. Additionally, we identified the regulatory pathway underlying osteoclast cell-cell fusion, which was enhanced by propofol through p38-mediated DC-STAMP expression.

Continuous application of compressive force induces fusion of osteoclast-like RAW264.7 cells via upregulation of RANK and downregulation of LGR4

AIMS

During orthodontic treatment, facilitating osteoclastic bone resorption in the alveolar bone exposed to the compressive force (CF) is an important factor for tooth movement. The present study investigated the effect of CF stimulation on the differentiation of RAW264.7 cells from precursors to mature osteoclasts.

MAIN METHODS

The cells were continuously stimulated with 0.3, 0.6, or 1.1 g/cm² CF-which was generated by increasing the volume of culture medium in the wells of a 96-well plate-in the presence or absence of receptor activator of nuclear factor κB (RANK) ligand (RANKL) for 4 days.

KEY FINDINGS

In the presence of RANKL, the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells and the mRNA levels of dendritic cell-specific transmembrane protein (DC-STAMP) and osteoclast-stimulatory transmembrane protein (OC-STAMP) were increased by application of 0.6 and 1.1 g/cm² CF as compared to 0.3 g/cm² CF. The mRNA level of RANK was upregulated whereas that of leucine-rich repeat-containing G-protein-coupled receptor (LGR)4-another RANKL receptor was downregulated by 0.6 and 1.1 g/cm² CF as compared to 0.3 g/cm² CF in the absence of RANKL. The proportion of cells with nuclear translocation of the nuclear translocation of nuclear factor of activated T cells (NFAT)c1 was increased by 0.6 and 1.1 g/cm² CF in the presence of RANKL.

SIGNIFICANCE

Continuous application of CF induced the differentiation of RAW264.7 cells into TRAP-positive multinuclear cells by enhancing the expression of DC- and OC-STAMP and the nuclear translocation of NFATc1. This may result from the CF-induced increase in RANK and decrease in LGR4 expression.

Effect of remifentanil on pre-osteoclast cell differentiation in vitro

BACKGROUND

The structure and function of bone tissue is maintained through a constant remodeling process, which is maintained by the balance between osteoblasts and osteoclasts. The failure of bone remodeling can lead to pathological conditions of bone structure and function. Remifentanil is currently used as a narcotic analgesic agent in general anesthesia and sedation. However, the effect of remifentanil on osteoclasts has not been studied. Therefore, we investigated the effect of remifentanil on pre-osteoclast (pre-OCs) differentiation and the mechanism of osteoclast differentiation in the absence of specific stimulus.

METHODS

Pre-OCs were obtained by culturing bone marrow-derived macrophages (BMMs) in osteoclastogenic medium for 2 days and then treated with various concentration of remifentanil. The mRNA expression of NFATc1 and c-fos was examined by using real-time PCR. We also examined the effect of remifentanil on the osteoclast-specific genes TRAP, cathepsin K, calcitonin receptor, and DC-STAMP. Finally, we examined the influence of remifentanil on the migration of pre-OCs by using the Boyden chamber assay.

RESULTS

Remifentanil increased pre-OC differentiation and osteoclast size, but did not affect the mRNA expression of NFATc1 and c-fos or significantly affect the expression of TRAP, cathepsin K, calcitonin receptor, and DC-STAMP. However, remifentanil increased the migration of pre-OCs.

CONCLUSIONS

This study suggested that remifentanil promotes the differentiation of pre-OCs and induces maturation, such as increasing osteoclast size. In addition, the increase in osteoclast size was mediated by the enhancement of pre-OC migration and cell fusion.

Progranulin and a five transmembrane domain-containing receptor-like gene are the key components in receptor activator of nuclear factor κB (RANK)-dependent formation of multinucleated osteoclasts

Homeostatic bone remodeling is vital to maintain healthy bone tissue. Although the receptor activator of nuclear factor κB ligand (RANKL)/RANK axis is considered the master regulator of osteoclastogenesis, the underlying mechanisms including cell fusion remain incompletely defined. Here, we introduce a new axis in the formation of multinucleated cells via RANK signaling: the progranulin (PGRN)/PIRO (PGRN-induced receptor-like gene during osteoclastogenesis) axis. When mouse bone marrow-derived macrophages were stimulated with PGRN in the presence of RANKL, explosive OC formation was observed. PGRN knockdown experiments suggested that endogenous PGRN is an essential component of the RANKL/RANK axis. Our efforts for identifying genes that are induced by PGRN unveiled a remarkably induced (20-fold) gene named PIRO. Substantial PGRN and PIRO expression was detected after 2 and 3 days, respectively, suggesting that their sequential induction. PIRO was predicted to be a five transmembrane domain-containing receptor-like molecule. The tissue distribution of PGRN and PIRO mRNA expression suggested that bone marrow cells are the most suitable niche. Mouse and human PIRO are part of a multigene family. Knockdown experiments suggested that PIRO is a direct target for the formation of multinucleated cells by PGRN. PGRN levels were also substantially higher in ovariectomized mice than in sham control mice. These observations suggest that PGRN and PIRO form a new regulatory axis in osteoclastogenesis that is included in RANK signaling in cell fusion and OC resorption of osteoclastogenesis, which may offer a novel therapeutic modality for osteoporosis and other bone-associated diseases.

Transglutaminase 2-dependent deamidation of glyceraldehyde-3-phosphate dehydrogenase promotes trophoblastic cell fusion

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional protein as well as a classic glycolytic enzyme, and its pleiotropic functions are achieved by various post-translational modifications and the resulting translocations to intracellular compartments. In the present study, GAPDH in the plasma membrane of BeWo choriocarcinoma cells displayed a striking acidic shift in two-dimensional electrophoresis after cell-cell fusion induction by forskolin. This post-translational modification was deamidation of multiple glutaminyl residues, as determined by molecular mass measurement and tandem mass spectrometry of acidic GAPDH isoforms. Transglutaminase (TG) inhibitors prevented this acidic shift and reduced cell fusion. Knockdown of the TG2 gene by short hairpin RNA reproduced these effects of TG inhibitors. Various GAPDH mutants with replacement of different numbers (one to seven) of Gln by Glu were expressed in BeWo cells. These deamidated mutants reversed the suppressive effect of wild-type GAPDH overexpression on cell fusion. Interestingly, the mutants accumulated in the plasma membrane, and this accumulation was increased according to the number of Gln/Glu substitutions. Considering that GAPDH binds F-actin via an electrostatic interaction and that the cytoskeleton is rearranged in trophoblastic cell fusion, TG2-dependent GAPDH deamidation was suggested to participate in actin cytoskeletal remodeling.

RANKL induces heterogeneous DC-STAMP(lo) and DC-STAMP(hi) osteoclast precursors of which the DC-STAMP(lo) precursors are the master fusogens

Osteoclasts (OC) are multinucleated bone resorbing cells that form via RANKL-induced fusion of heterogeneous mononuclear OC precursors (OCP). Currently, there are no unique surface markers to distinguish these OCP populations, which are diagnostic for erosive and metabolic bone diseases using culture assays. Thus, we investigated expression of DC-STAMP, a surface receptor required for OCP fusion, during osteoclastogenesis in vitro using a novel monoclonal antibody (1A2). Immunoprecipitation-Western blot analysis of OCP membrane proteins detected 106 kDa dimeric and 53 kDa monomeric DC-STAMP in non-denaturing and denaturing conditions, respectively, with greater sensitivity versus rabbit anti-sera (KR104). 1A2 also detected 99.9% of undifferentiated monocytes as a single population by flow cytometry with a MFI 100-fold over background, while KR104 was not useful in this assay. Functionally, 1A2 inhibited OCP fusion in vitro. RANKL stimulation of OCP induced DC-STAMP(lo) and DC-STAMP(hi) cells, which mature into OC and mononuclear cells respectively as determined by fluorescent microscopy and TRAP assays. Addition of DC-STAMP(hi) cells to purified DC-STAMP(lo) cultures produced larger, more nucleated OC vs. pure DC-STAMP(lo) cultures. RT-qPCR analysis of these two populations showed that OC markers (Trap and Oc-stamp) and fusogenic gene expression (Cd9 and Cd47), were significantly increased in DC-STAMP(lo) vs. DC-STAMP(hi) cells. Collectively, these results demonstrate that DC-STAMP is expressed on OCP as a dimer, which is efficiently detected by 1A2 via flow cytometry. RANKL induces osteoclastogenesis by stimulating DC-STAMP internalization in some OCP, and these DC-STAMP(lo) cells display the "master fusogen" phenotype. In contrast, DC-STAMP(hi) OCP can only act as mononuclear donors.