Cellular study of the LPS-induced osteoclastic multinucleated cell formation from RAW264.7 cells

A review of bacterial and osteoclast differentiation in bone infection

Bone infections are characterized by bacterial invasion of the bone microenvironment and subsequent bone structure deterioration. This holds significance because osteoclasts, which are the only cells responsible for bone resorption, are abnormally stimulated during bone infections. Multiple communication factors secreted by bone stromal cells regulate the membrane of osteoclast progenitor cells, thereby maintaining bone homeostasis through the expression of many types of receptors. During infection, the immunoinflammatory response triggered by bacterial invasion and multiple virulence factors of bacterial origin can disrupt osteoclast homeostasis. Therefore, clarifying the pathways through which bacteria affect osteoclasts can offer a theoretical basis for preventing and treating bone infections. This review summarizes studies investigating bone destruction caused by different bacterial infections. In conclusion, bacteria can affect osteoclast metabolic activity through multiple pathways, including direct contact, release of virulence factors, induction of immunoinflammatory responses, influence on bone stromal cell metabolism, and intracellular infections.

Zoledronic Acid Inhibits Lipopolysaccharide-Induced Osteoclastogenesis by Suppressing Macrophage NLRP3-Mediated Autophagy Pathway

INTRODUCTION

Inflammatory factors leading to bone loss significantly increase the risk of tooth loosening or implantation failure. Zoledronic acid (ZOL) is a widely used medication for effectively inhibiting excessive bone destruction, but its effect on alleviating inflammatory bone loss remains to be elucidated. In this study, we investigated whether ZOL alleviates inflammatory bone resorption through immunomodulatory effect.

METHODS

The viability of the cells was evaluated by Cell Counting Kit 8 (CCK8) assay. Osteoclast (OC) differentiation and function were determined by tartrate-resistant acid phosphatase (TRAP) staining and bone resorption pits assays, respectively. Autophagosomes and actin ring structures of OC were observed using transmission electron microscopy (TEM) and F-actin ring staining, respectively. The microstructure in mice maxillary alveolar bone model was observed by micro computed tomography (Miro-CT). Reverse transcription-quantitative PCR (RT-qPCR) to detect the mRNA expression of osteoclast-related genes and Western blot (WB) analysis to evaluate the protein expression levels of autophagy-related proteins and the NOD-like receptor family pyrin domain-containing protein 3 (NLRP3)-related proteins in pre-OCs.

RESULTS

The findings indicated that ZOL hindered lipopolysaccharide (LPS)-mediated OC differentiation, formation, bone resorption activity and autophagosome levels. Furthermore, ZOL diminished the expression of genes associated with OC. And the expression of proteins ATG7, LC3II, Beclin1, NLRP3-related proteins and tumor necrosis factor-α (TNF-α) protein were markedly decreased while P62 was increased, especially in the 1 μM ZOL group or MCC950 + ZOL group.

CONCLUSIONS

ZOL has a certain immunomodulatory effect that exhibits anti-inflammatory properties at lower concentrations, which can weaken LPS-induced OCs differentiation and function, and NLRP3-mediated autophagy pathway may participate in this process.

The role of autophagy in SIM mediated anti-inflammatory osteoclastogenesis through NLRP3 signaling pathway

BACKGROUND

Inflammatory bone resorption is a prominent risk factor for implantation failure. Simvastatin (SIM) has anti-inflammatory effects independent of cholesterol lowering and reduces osteoclastogenesis by decreasing both the number and activity of osteoclasts. However, the specific mechanism of inflammatory bone loss alleviation by SIM remains to be elucidated. We hypothesized that SIM relieves inflammatory bone loss by modulating autophagy and suppressing the NOD-like receptor family pyrin domain-containing protein 3 (NLRP3) signaling pathway.

METHODS AND RESULTS

RAW264.7 cells were stimulated by lipopolysaccharide (LPS) after being pretreated with various concentrations of SIM. Osteoclast (OC) differentiation, formation and activity were evaluated by tartrate-resistant acid phosphatase staining, F-actin ring staining and bone resorption pit assays, respectively. We observed autophagosomes by transmission electron microscopy. Then NLRP3 inhibitor MCC950 was used to further explore the corresponding molecular mechanism underlying anti-inflammatory bone resorption, the expression of autophagy-related proteins and NLRP3 signaling pathway factors in pre-OCs were evaluated by western blot analysis, and the expression of OC-specific molecules was analyzed using reverse transcription-quantitative polymerase chain reaction. The results showed that SIM decreased the expression of tumor necrosis factor-α, whereas increased Interleukin-10. In addition, SIM inhibited LPS-induced OC differentiation, formation, bone resorption activity, the level of autophagosomes, and OC-specific markers. Furthermore, SIM significantly suppressed autophagy by downregulating LC3II, Beclin1, ATG7, and NLRP3-related proteins expression while upregulating P62 under inflammatory conditions.

CONCLUSIONS

SIM may reduce autophagy secretion to attenuate LPS-induced osteoclastogenesis and the NLRP3 signaling pathway participates in this process, thus providing theoretical basis for the application of this drug in peri-implantitis.

The Marine Factor 3,5-dihydroxy-4-methoxybenzyl Alcohol Suppresses Cell Growth, Inflammatory Cytokine Production, and NF-κB Signaling-enhanced Osteoclastogenesis in In vitro Mouse Macrophages RAW264.7 Cells

BACKGROUND AND OBJECTIVE

The novel marine factor 3,5-dihydroxy-4- methoxybenzyl alcohol (DHMBA) was originally identified in the Pacific oyster Crassostrea Gigas. DHMBA has been shown to prevent oxidative stress by scavenging radicals and enhance the production of antioxidant proteins. However, the pharmacologic role of DHMBA has been poorly understood. Inflammation is implicated in the pathogenesis of many diseases. Inflammatory cytokines are produced in macrophages with stimulation of lipopolysaccharide (LPS) and are used as biomarkers that cause diverse disease conditions. Therefore, this study has been undertaken to elucidate whether DHMBA expresses anti-inflammatory effects in in vitro mouse macrophage RAW264.7 cells.

METHODS

Mouse macrophage RAW264.7 cells were cultured in a medium containing 10% fetal bovine serum (FBS) with or without DHMBA (1-1000 μM).

RESULTS

Culturing with DHMBA (1-1000 μM) suppressed the growth and stimulated the death of RAW264.7 cells in vitro, leading to a decrease in cell number. Treatment with DHMBA reduced the levels of Ras, PI3K, Akt, MAPK, phospho-MAPK, and mTOR, which are signalling factors to promote cell proliferation, and it raised the levels of p53, p21, Rb, and regucalcin, which are cell growth suppressors. DHMBA treatment elevated caspase-3 and cleaved caspase-3 levels. Interestingly, DHMBA treatment repressed the production of inflammatory cytokines, including tumor necrosis factor-α, interleukin-6, interleukin-1β, or prostaglandin E2, which were enhanced by LPS stimulation. Notably, the levels of NF-κB p65 were increased by LPS treatment, and this augmentation was repres-sed by DHMBA treatment. Moreover, LPS treatment stimulated osteoclastogenesis of RAW264.7 cells. This stimulation was blocked by DHMBA treatment, and this effect was not caused by the presence of an NF-κB signalling inhibitor.

CONCLUSION

DHMBA was found to potentially suppress the activity of inflammatory macrophages in vitro, suggesting its therapeutic usefulness in inflammatory conditions.

Staphylococcus aureus enhances osteoclast differentiation and bone resorption by stimulating the NLRP3 inflammasome pathway

BACKGROUND

Osteomyelitis is one of the most challenging infectious diseases and is mainly caused by Staphylococcus aureus (S. aureus). In this study, we analyzed the effect of S. aureus on osteoclast differentiation and its possible molecular mechanism.

METHODS

We cultured RAW 264.7 cells with live S. aureus for 5 days. We assessed cell viability and the formation of resorption pits. We tested the NLRP3 inflammasome signaling pathways and measured the mRNA expression levels of osteoclastspecific genes, including TRAP, MMP9, cathepsin K, calcitonin receptor and ATP6V0d2. Furthermore, we analyzed the protein expression levels of the protein in the NF-κB and p38 MAPK signaling pathways to clarify the signaling pathways by which S. aureus promotes osteoclast differentiation.

RESULTS

Staphylococcus aureus induced NLRP3 inflammasome activation. S. aureus promoted bone resorption and enhanced the expression of osteoclastspecific genes, such as TRAP, MMP9, cathepsin K, calcitonin receptor and ATP6V0d2. MCC950 was used to inhibit NLRP3 inflammasome activity. Osteoclast differentiation and the expression of osteoclastspecific genes induced by S. aureus were inhibited by MCC950 pretreatment. The degradation of IκBα and phosphorylation of P65 were increased under the induction of S. aureus, but proteins in the p38 MAPK signaling pathway did not change significantly.

CONCLUSION

Staphylococcus aureus induces osteoclast differentiation and promotes bone resorption in vitro, and the NLRP3 inflammasome signaling pathway plays a significant role in this process. S. aureus-induced NLRP3 inflammasome activation was mainly dependent on the NF-κB signaling pathway during osteoclastogenesis.

Glycobiology in osteoclast differentiation and function

Glycans, either alone or in complex with glycan-binding proteins, are essential structures that can regulate cell biology by mediating protein stability or receptor dimerization under physiological and pathological conditions. Certain glycans are ligands for lectins, which are carbohydrate-specific receptors. Bone is a complex tissue that provides mechanical support for muscles and joints, and the regulation of bone mass in mammals is governed by complex interplay between bone-forming cells, called osteoblasts, and bone-resorbing cells, called osteoclasts. Bone erosion occurs when bone resorption notably exceeds bone formation. Osteoclasts may be activated during cancer, leading to a range of symptoms, including bone pain, fracture, and spinal cord compression. Our understanding of the role of protein glycosylation in cells and tissues involved in osteoclastogenesis suggests that glycosylation-based treatments can be used in the management of diseases. The aims of this review are to clarify the process of bone resorption and investigate the signaling pathways mediated by glycosylation and their roles in osteoclast biology. Moreover, we aim to outline how the lessons learned about these approaches are paving the way for future glycobiology-focused therapeutics.

Evaluation of culture conditions for osteoclastogenesis in RAW264.7 cells

Osteoclasts are the only multinucleated cells in vivo responsible for bone resorption and are vital for regulating bone remodeling and maintaining bone mass. The RAW264.7 cell line is widely used to study osteoclastic differentiation and biological molecular mechanism. However, protocols for inducing osteoclast formation in RAW264.7 cells vary considerably between laboratories, hindering the replication of results. Therefore, we tested the influence of culture conditions on osteoclast differentiation, including cell density and receptor activator of nuclear factor kappa-B ligand (RANKL) concentrations with or without macrophage colony-stimulating factors (M-CSF). Tartrate-resistant acid phosphatase (TRAP) staining was used to detect the morphology of osteoclasts. qPCR was used to detect gene expression of osteoclast-specific gene marker cathepsin K (CTSK), osteoclast transcription factors c-Fos and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1). The bone resorption function was evaluated by a scanning electron microscope (SEM). RANKL treatment increased multinucleated osteoclasts formation and increased CTSK, c-Fos and NFATc1 gene expression. Compared with RANKL treatment, M-CSF significantly decreased multinucleated osteoclasts formation, reduced CTSK gene expression and had little effect on c-Fos and NFATc1 gene expression. Concerning bone resorption activity, RANKL treatment increased bone resorption pits on bovine bone slices. Significantly higher levels of osteoclastogenesis were observed with RAW264.7-cell density of 2×104 cells/well in 24-well plates. Our results suggest that the addition of 50 ng/ml M-CSF has no positive effect on osteoclastogenesis. RANKL treatment and cell density contribute to osteoclast formation, and the optimal conditions are beneficial when exploring osteoclast function and mechanism.

Age-related accumulation of advanced oxidation protein products promotes osteoclastogenesis through disruption of redox homeostasis

Enhanced osteoclastogenesis is one of the major causes of age-related bone loss. Aging is accompanied by accumulation of advanced oxidation protein products (AOPPs). However, whether AOPPs accumulation contributing to the osteoclastogenesis with aging remains unclear. Here, we showed that AOPPs accumulation was associated with the enhanced osteoclastogenesis and deterioration of bone microstructure in aged mice. In vitro, AOPPs directly induced osteoclastogenesis by interaction with receptor activator of nuclear factor κ B (RANK) and the receptor for advanced glycation end products (RAGE) in the primary bone marrow monocytes. Bindings of AOPPs to RANK and RAGE were able to activate nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, trigger generation of reactive oxygen species, then induce phosphorylation of mitogen-activated protein kinases and c-fos, upregulation of the nuclear factor of activated T cell c1, eventually induce bone marrow monocytes to differentiate into mature osteoclasts. Chronic exposure to AOPPs enhanced osteoclastogenesis and bone loss in mice, which could be alleviated by NADPH oxidase inhibitor apocynin. Local injection of AOPPs into subperiosteal area induced bone resorption at the site of administration, which was similar to the effect of RANK ligand. Together, these results suggested that AOPPs could serve as a novel regulator of osteoclastogenesis and AOPPs accumulation might play an important role in the development of age-related bone loss.

Cell cytoskeleton and proliferation study for the RANKL-induced RAW264.7 differentiation

Although document studies (including ours) have been reported the achieved in vitro osteoclastic cellular model establishment from the RAW264.7 cell lineage, there was no study directly reported that American Type Culture Collection (ATCC) cell bank has various RAW264.7 cell lineages. Besides that, for our knowledge there was only one study compared the two different RAW264.7TIB-71 and RAW264.7CRL-2278 cell lineages for their osteoclastic differentiation, and they concluded that the RAW264.7CRL-2278 demonstrated to generate much osteoclast than RAW264.7TIB-71 . However, on the contrary to their results we noticed the fusion of RAW264.7TIB-71 in our previous studies was much compromising. Therefore, we try to explore the two cell lineages for their properties in osteoclastic differentiation with an in-depth cellular cytoskeletal study. Our current study has showed that comparing to the RAW264.7CRL-2278 , RAW264.7TIB-71 demonstrated a much higher efficacies for RANKL-stimulated osteoclastic differentiation. Besides that, in our depth cytoskeletal studies, we found that the RANKL-induced RAW264.7TIB-71 cells could finally differentiate into mature osteoclasts. However, regardless the various pre-treatment conditions, there was no mature osteoclast formed in RANKL-induced RAW264.7CRL-2278 cell lineage.