Long-Lasting Activity of ERK Kinase Depends on NFATc1 Induction and Is Involved in Cell Migration-Fusion in Murine Macrophages RAW264.7

Unveiling the potential of Butylphthalide: inhibiting osteoclastogenesis and preventing bone loss

Osteoporosis, resulting from overactive osteoclasts and leading to elevated fracture risk, has emerged as a global public health concern due to the aging population. Therefore, inhibiting osteoclastogenesis and bone resorption function represents a crucial approach for preventing and treating osteoporosis. The purpose of this study was to examine the effects and molecular mechanisms of Butylphthalide (NBP) on the differentiation and function of osteoclasts induced by RANKL. Osteoclastogenesis was assessed through TRAP staining and bone slice assay. An animal model that underwent ovariectomy, simulating postmenopausal women's physiological characteristics, was established to investigate the impact of Butylphthalide on ovariectomy-induced bone loss. To delve deeper into the specific mechanisms, we employed Western blot, PCR, immunofluorescence, and immunohistochemical staining to detect the expression of proteins that are associated with the osteoclast signaling pathway. In this study, we found that Butylphthalide not only suppressed osteoclastogenesis and bone resorption in vitro but also significantly decreased TRAcP-positive osteoclasts and prevented bone loss in vivo. Further mechanistic experiments revealed that Butylphthalide reduces intracellular ROS in osteoclasts, inhibits the MAPK and NFATc1 signaling pathways, and downregulates the key genes and proteins of osteoclasts. This inhibits osteoclast formation and function. The reduction in ROS in osteoclasts is intricately linked to the activity of Butylphthalide-modulated antioxidant enzymes. Overall, NBP may offer a alternative treatment option with fewer side effects for skeletal diseases such as osteoporosis.

Extracellular Signal-Regulated Kinases Play Essential but Contrasting Roles in Osteoclast Differentiation

Bone homeostasis is regulated by the balanced actions of osteoblasts that form the bone and osteoclasts (OCs) that resorb the bone. Bone-resorbing OCs are differentiated from hematopoietic monocyte/macrophage lineage cells, whereas osteoblasts are derived from mesenchymal progenitors. OC differentiation is induced by two key cytokines, macrophage colony-stimulating factor (M-CSF), a factor essential for the proliferation and survival of the OCs, and receptor activator of nuclear factor kappa-B ligand (RANKL), a factor for responsible for the differentiation of the OCs. Mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinases (ERKs), p38, and c-Jun N-terminal kinases, play an essential role in regulating the proliferation, differentiation, and function of OCs. ERKs have been known to play a critical role in the differentiation and activation of OCs. In most cases, ERKs positively regulate OC differentiation and function. However, several reports present conflicting conclusions. Interestingly, the inhibition of OC differentiation by ERK1/2 is observed only in OCs differentiated from RAW 264.7 cells. Therefore, in this review, we summarize the current understanding of the conflicting actions of ERK1/2 in OC differentiation.

Role of CELF2 in ferroptosis: Potential targets for cancer therapy (Review)

Ferroptosis is a novel form of regulated cellular necrosis that plays a critical role in promoting cancer progression and developing drug resistance. The main characteristic of ferroptosis is iron‑dependent lipid peroxidation caused by excess intracellular levels of reactive oxygen species. CUGBP ELAV‑like family number 2 (CELF2) is an RNA‑binding protein that is downregulated in various types of cancer and is associated with poor patient prognoses. CELF2 can directly bind mRNA to a variety of ferroptosis control factors; however, direct evidence of the regulatory role of CELF2 in ferroptosis is currently limited. The aim of the present review was to summarise the findings of previous studies on CELF2 and its role in regulating cellular redox homeostasis. The present review may provide insight into the possible mechanisms through which CELF2 affects ferroptosis and to provide recommendations for future studies.

Isosinensetin alleviates estrogen deficiency-induced osteoporosis via suppressing ROS-mediated NF-κB/MAPK signaling pathways

The formation of osteoclasts and their hyperactive bone resorption are related to the aggregation of intracellular reactive oxygen species (ROS). Flavonoids, derived from plant active ingredients, can alleviate the symptoms of osteoporosis (OP). Isosinensetin (Iss) is a flavonoid with antioxidant effects obtained mainly from citrus fruits, and its effect on osteoclastogenesis has not been reported. In this study, we investigated the antioxidant activity of Iss on osteoclast differentiation and function, as well as the therapeutic impact of Iss on OP. We found that Iss inhibited osteoclastogenesis and suppressed the bone resorption function of osteoclasts. Additionally, Iss reduced receptor activator of nuclear factor-κB ligand (RANKL)-induced intracellular ROS. Using quantitative real-time polymerase chain reaction and western blot, we further found that Iss inhibited osteoclast-specific genes and related proteins, while promoting the expression of antioxidant enzyme-related genes and proteins. Mechanistically, Iss reduces intracellular ROS by activating nuclear factor-erythroid 2-related factor 2 (Nrf2) and its related antioxidant enzymes and inhibits the downstream nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways of ROS, which in turn inhibits nuclear factor of activated T cells 1 (NFATc1), and ultimately inhibits osteoclastogenesis. In vivo, by micro-computed tomography (Micro-CT) assay and histological analyses, we found that Iss could reduce bone loss in ovariectomized (OVX) mice. Therefore, Iss has the potential as an OP preventative and therapeutic drug option.

Graphene Oxide-Modified Concentric Microgrooved Titanium Surfaces for the Dual Effects of Osteogenesis and Antiosteoclastogenesis

Surface modification is an effective method to resolve the biocompatibility, mechanical, and functional issues of various titanium implant materials. Therefore, many researchers have modified the implant surface to promote the osseointegration of the implant and improve the implant survival rate. In this study, we used photolithography to construct concentric microgrooves with widths of 10 μm and depths of 10 μm, to produce an osteon-mimetic concentric microgrooved titanium surface that was further modified with graphene oxide by silanization (GO-CMS). The modified surface had great biocompatibility and promoted the proliferation of bone marrow-derived mesenchymal stem cells (BMSCs) and RAW264.7 macrophages. The concentric microgrooves on the titanium surface guided cell migration, altered actin cytoskeleton, and caused the cells to arrange in concentric circles. The titanium surface of the GO-modified osteon-mimetic concentric microgrooves promoted the osteogenic differentiation of BMSCs and inhibited the osteoclastogenic differentiation of RAW264.7 cells. Subsequently, we constructed an indirect coculture system and found that RAW264.7 cells cultured on a GO-CMS material surface in a BMSC-conditioned medium (BCM) decreased receptor activator of nuclear factor-κB ligand (RANKL) secretion and increased OPG secretion and also that the BCM inhibited osteoclastogenic differentiation. Additionally, the secretion of OSM increased in BMSCs cultured in RAW264.7-conditioned medium (RCM) in the GO-CMS group, which in turn promoted the osteogenic differentiation of BMSCs. In conclusion, the titanium surface of GO-modified osteon-mimetic concentric microgrooves had dual effects of osteogenesis and antiosteoclastogenesis under single and coculture conditions, which is beneficial for implant osseointegration and is a promising method for the future direction of surface modifications of implants.

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.

Roburic acid attenuates osteoclastogenesis and bone resorption by targeting RANKL-induced intracellular signaling pathways

Excessive activity of osteoclasts contributes to skeletal diseases such as osteoporosis and osteolysis. However, current drugs targeting osteoclast have various deficiencies, placing natural compounds as substitutions of great potential. Roburic acid (RA) is a triterpenoid exacted from Radix Gentianae Macrophyllae, which exhibits inhibitory effects on inflammation and oxidation. By employing an in vitro osteoclastogenesis model, this study investigates the effects and mechanisms of RA on intracellular signaling induced by receptor activator of nuclear factor-κB ligand (RANKL). As expected, RA at a concentration scope from 1 to 10 μM dampened the osteoclast differentiation of bone marrow macrophages (BMMs) but without cell toxicity. Interestingly, RA showed no effect on osteoblastogenesis in vitro. Furthermore, RA mitigated F-actin ring formation, hydroxyapatite resorption, and gene expression in osteoclasts. Mechanistically, RA suppressed TNF receptor-associated factor 6 (TRAF6), the crucial adaptor protein following RANKL-RANK binding. On the one hand, RA downregulated the nuclear factor-κB (NF-κB) activity, extracellular regulated protein kinases (ERK) phosphorylation, and calcium oscillations. On the other hand, RA upregulated the antioxidative response element (ARE) response and the protein expression of heme oxygenase (HO)-1. These upstream alterations eventually led to the suppression of the nuclear factor of activated T cells 1 (NFATc1) activity and the expression of proteins involved in osteoclastogenesis and bone resorption. Furthermore, by using an ovariectomized (OVX) mice model, RA was found to have therapeutic effects against bone loss. On account of these findings, RA could be used to restrain osteoclasts for treating osteoporosis and other osteolytic diseases.

MiRNAs Expression Profiling in Raw264.7 Macrophages after Nfatc1-Knockdown Elucidates Potential Pathways Involved in Osteoclasts Differentiation

Differentiation of macrophages toward osteoclasts is crucial for bone homeostasis but can be detrimental in disease states, including osteoporosis and cancer. Therefore, understanding the osteoclast differentiation process and the underlying regulatory mechanisms may facilitate the identification of new therapeutic targets. Hereby, we tried to reveal new miRNAs potentially involved in the regulation of early steps of osteoclastogenesis, with a particular focus on those possibly correlated with NFATc1 expression, by studying miRNAs profiling. During the first 24 h of osteoclastogenesis, 38 miRNAs were differentially expressed between undifferentiated and RANKL-stimulated RAW264.7 cells, while 10 miRNAs were differentially expressed between RANKL-stimulated cells transfected with negative control or NFATc1-siRNAs. Among others, the expression levels of miR-411, miR-144 and members of miR-29, miR-30, and miR-23 families changed after RANKL stimulation. Moreover, the potential role of miR-124 during osteoclastogenesis was explored by transient cell transfection with anti-miR-124 or miR-124-mimic. Two relatively unknown miRNAs, miR-880-3p and miR-295-3p, were differentially expressed between RANKL-stimulated/wild-type and RANKL-stimulated/NFATc1-silenced cells, suggesting their possible correlation with NFATc1. KEGG enrichment analyses showed that kinase and phosphatase enzymes were among the predicted targets for many of the studied miRNAs. In conclusion, our study provides new data on the potential role and possible targets of new miRNAs during osteoclastogenesis.

Osteoclasts Differentiation from Murine RAW 264.7 Cells Stimulated by RANKL: Timing and Behavior

The development of multi-nucleated cells is critical for osteoclasts (OCs) maturation and function. Our objective was to extend knowledge on osteoclastogenesis, focusing on pre-OC fusion timing and behavior. RAW 264.7 cells, which is a murine monocyte-macrophage cell line, provide a valuable and widely used tool for in vitro studies on osteoclastogenesis mechanisms. Cells were treated with the receptor activator of nuclear factor κ-B ligand (RANKL) for 1-4 days and effects on cell morphology, cytoskeletal organization, protein distribution, and OC-specific gene expression examined by TEM, immunofluorescence, and qPCR. Multinucleated cells began to appear at two days of Receptor Activator of Nuclear factor κ-B Ligand (RANKL) stimulation, increasing in number and size in the following days, associated with morphological and cytoskeletal organization changes. Interesting cellular extensions were observed in three days within cells labeled with wheat germ agglutinin (WGA)-Fluorescein isothiocyanate (FITC). The membrane, cytoplasmic, or nuclear distribution of RANK, TRAF6, p-p38, pERK1/2, and NFATc1, respectively, was related to OCs maturation timing. The gene expression for transcription factors regulating osteoclastogenesis (NFATc1, c-fos, RelA, MITF), molecules involved in RANKL-signaling transduction (TRAF6), cytoskeleton regulation (RhoA), fusion (DC-STAMP), migration (MMP9), and OC-specific enzymes (TRAP, CtsK), showed different trends related to OC differentiation timing. Our findings provide an integrated view on the morphological and molecular changes occurring during RANKL stimulation of RAW 264.7 cells, which are important to better understand the OCs' maturation processes.