Signaling Pathways in Osteoclast Differentiation

In Vitro Cell Culture Model for Osteoclast Activation during Estrogen Withdrawal

Estrogen (17β-estradiol) deficiency post-menopause alters bone homeostasis whereby bone resorption by osteoclasts exceeds bone formation by osteoblasts, leading to osteoporosis in females. We established an in vitro model to examine the consequences of estrogen withdrawal (E2-WD) on osteoclasts derived from the mouse macrophage RAW 264.7 cell line and utilized it to investigate the mechanism behind the enhanced osteoclast activity post-menopause. We found that a greater population of osteoclasts that underwent E2-WD contained a podosome belt necessary for osteoclasts to adhere and resorb bone and possessed elevated resorptive activity compared to osteoclasts exposed to estrogen (E2) continuously. Our results show that compared to osteoclasts that received E2 continuously, those that underwent E2-WD had a faster rate of microtubule (MT) growth, reduced RhoA activation, and shorter podosome lifespan. Thus, altered podosome and MT dynamics induced by the withdrawal of estrogen supports podosome belt assembly/stability in osteoclasts, which may explain their enhanced bone resorption activity.

Quercetin in Osteoporosis Treatment: A Comprehensive Review of Its Mechanisms and Therapeutic Potential

PURPOSE OF REVIEW

This review aims to provide a theoretical basis and insights for quercetin's clinical application in the prevention and treatment of osteoporosis (OP), analyzing its roles in bone formation promotion, bone resorption inhibition, anti-inflammation, antioxidant effects, and potential mechanisms.

RECENT FINDINGS

OP, a prevalent bone disorder, is marked by reduced bone mineral density and impaired bone architecture, elevating the risk of fractures in patients. The primary approach to OP management is pharmacotherapy, with quercetin, a phytochemical compound, emerging as a focus of recent interest. This natural flavonoid exerts regulatory effects on bone marrow mesenchymal stem cells, osteoblasts, and osteoclasts and promotes bone health and metabolic equilibrium via anti-inflammatory and antioxidative pathways. Although quercetin has demonstrated significant potential in regulating bone metabolism, there is a need for further high-quality clinical studies focused on medicinal quercetin.

A comprehensive review and advanced biomolecule-based therapies for osteoporosis

BACKGROUND

The prevalence of osteoporosis (OP) on a global scale is significantly elevated that causes life threatening issues. The potential of groundbreaking biomolecular therapeutics in the field of OP is highly encouraging. The administration of biomolecular agents has the potential to mitigate the process of bone demineralization while concurrently augmenting the regenerative capacity of bone tissue, thereby facilitating a personalized therapeutic approach. Biomolecules-based therapies showed promising results in term of bone mass protection and restoration in OP.

AIM OF REVIEW

We summarized the recent biomolecular therapies with notable progress in clinical, demonstrating the potential to transform illness management. These treatments frequently utilize different biomolecule based strategies. Biomolecular therapeutics has a targeted character, which results in heightened specificity and less off-target effects, ultimately leading to increased patient outcomes. These aspects have the capacity to greatly enhance the management of OP, thus resulting in a major enhancement in the quality of life encountered by individuals affected by this condition.

Microdroplets Encapsulated with NFATc1-siRNA and Exosomes-Derived from MSCs Onto 3D Porous PLA Scaffold for Regulating Osteoclastogenesis and Promoting Osteogenesis

Introduction

Osteoporotic-related fractures remains a significant public health concern, thus imposing substantial burdens on our society. Excessive activation of osteoclastic activity is one of the main contributing factors for osteoporosis-related fractures. While polylactic acid (PLA) is frequently employed as a biodegradable scaffold in tissue engineering, it lacks sufficient biological activity. Microdroplets (MDs) have been explored as an ultrasound-responsive drug delivery method, and mesenchymal stem cell (MSC)-derived exosomes have shown therapeutic effects in diverse preclinical investigations. Thus, this study aimed to develop a novel bioactive hybrid PLA scaffold by integrating MDs-NFATc1-silencing siRNA to target osteoclast formation and MSCs-exosomes (MSC-Exo) to influence osteogenic differentiation (MDs-NFATc1/PLA-Exo).

Methods

Human bone marrow-derived mesenchymal stromal cells (hBMSCs) were used for exosome isolation. Transmission electron microscopy (TEM) and confocal laser scanning microscopy were used for exosome and MDs morphological characterization, respectively. The MDs-NFATc1/PLA-Exo scaffold was fabricated through poly(dopamine) and fibrin gel coating. Biocompatibility was assessed using RAW 264.7 macrophages and hBMSCs. Osteoclast formations were examined via TRAP staining. Osteogenic differentiation of hBMSCs and cytokine expression modulation were also investigated.

Results

MSC-Exo exhibited a cup-shaped structure and effective internalization into cells, while MDs displayed a spherical morphology with a well-defined core-shell structure. Following ultrasound stimulation, the internalization study demonstrated efficient delivery of bioactive MDs into recipient cells. Biocompatibility studies indicated no cytotoxicity of MDs-NFATc1/PLA-Exo scaffolds in RAW 264.7 macrophages and hBMSCs. Both MDs-NFATc1/PLA and MDs-NFATc1/PLA-Exo treatments significantly reduced osteoclast differentiation and formation. In addition, our results further indicated MDs-NFATc1/PLA-Exo scaffold significantly enhanced osteogenic differentiation of hBMSCs and modulated cytokine expression.

Discussion

These findings suggest that the bioactive MDs-NFATc1/PLA-Exo scaffold holds promise as an innovative structure for bone tissue regeneration. By specifically targeting osteoclast formation and promoting osteogenic differentiation, this hybrid scaffold may address key challenges in osteoporosis-related fractures.

Basic-helix-loop-helix family member e41 suppresses osteoclastogenesis and abnormal bone resorption disease via NFATc1

Overactivation of osteoclasts due to altered osteoclastogenesis causes multiple bone metabolic diseases. However, how osteoclast differentiation is tightly regulated and involved in multiple pathophysiological states remains mystery. In this study, we noticed that the downregulation of BHLHE41 (basic-helix-loop-helix family member e41) was tightly associated with osteoclast differentiation and osteoporosis. Functionally, the upregulation or downregulation of BHLHE41 suppressed or promoted osteoclast differentiation, respectively, in vitro. A mechanism study indicated that the direct binding of BHLHE41 to the promoter region of NFATc1 that led to its downregulation. Notably, the inhibition of NFATc1 abrogated the enhanced osteoclast differentiation in BHLHE41-knockdown bone marrow macrophages (BMMs). Additionally, upregulation of BHLHE41 impeded bone destruction in OVX mice with osteoporosis. Therefore, our research reveals the mechanism by which BHLHE41 regulates osteoclast differentiation and bone resorption via NFATc1, and targeting BHLHE41 is a potential strategy for the treatment of osteoporosis.

Infrapatellar fat pad adipose tissue-derived macrophages display a predominant CD11c+CD206+ phenotype and express genotypes attributable to key features of OA pathogenesis

Objectives

In knee osteoarthritis (OA), macrophages are the most predominant immune cells that infiltrate synovial tissues and infrapatellar fat pads (IPFPs). Both M1 and M2 macrophages have been described, but their role in OA has not been fully investigated. Therefore, we investigated macrophage subpopulations in IPFPs and synovial tissues of knee OA patients and their correlation with disease severity, examined their transcriptomics, and tested for factors that influenced their polarization.

Methods

Synovial tissues and IPFPs were obtained from knee OA patients undergoing total knee arthroplasty. Macrophages isolated from these joint tissues were characterized via flow cytometry. Transcriptomic profiling of each macrophage subpopulations was performed using NanoString technology. Peripheral blood monocyte-derived macrophages (MDMs) were treated with synovial fluid and synovial tissue- and IPFP-conditioned media. Synovial fluid-treated MDMs were treated with platelet-rich plasma (PRP) and its effects on macrophage polarization were observed.

Results

Our findings show that CD11c+CD206+ macrophages were predominant in IPFPs and synovial tissues compared to other macrophage subpopulations (CD11c+CD206-, CD11c-CD206+, and CD11c-CD206- macrophages) of knee OA patients. The abundance of macrophages in IPFPs reflected those in synovial tissues but did not correlate with disease severity as determined from Mankin scoring of cartilage destruction. Our transcriptomics data demonstrated highly expressed genes that were related to OA pathogenesis in CD11c+CD206+ macrophages than CD11c+CD206-, CD11c-CD206+, and CD11c-CD206- macrophages. In addition, MDMs treated with synovial fluid, synovial tissue-conditioned media, or IPFP-conditioned media resulted in different polarization profiles of MDMs. IPFP-conditioned media induced increases in CD86+CD206+ MDMs, whereas synovial tissue-conditioned media induced increases in CD86+CD206- MDMs. Synovial fluid treatment (at 1:8 dilution) induced a very subtle polarization in each macrophage subpopulation. PRP was able to shift macrophage subpopulations and partially reverse the profiles of synovial fluid-treated MDMs.

Conclusion

Our study provides an insight on the phenotypes and genotypes of macrophages found in IPFPs and synovial tissues of knee OA patients. We also show that the microenvironment plays a role in driving macrophages to polarize differently and shifting macrophage profiles can be reversed by PRP.

Farrerol suppresses osteoclast differentiation and postmenopausal osteoporosis by inhibiting the nuclear factor kappa B signaling pathway

Excessive bone resorption caused by upregulated osteoclast activity is a key factor in osteoporosis pathogenesis. Farrerol is a typical natural flavanone and exhibits various pharmacological actions. However, the role and mechanism of action of farrerol in osteoclast differentiation regulation remain unclear. This study aimed to evaluate the effects and mechanism of farrerol on the inhibition of osteoclastogenesis. Tartrate-resistant acid phosphatase staining, F-actin staining, and the pit formation assay were performed to examine the differentiation and functions of osteoclasts in vitro. The expression of proteins associated with the nuclear factor kappa B and mitogen-activated protein kinase signaling pathways was analyzed by western blotting. Dual X-ray absorptiometry, microcomputed tomography, and histopathological and immunohistochemical analyses were performed to determine the therapeutic effect of farrerol in vivo bone loss prevention. The effects of farrerol on osteoblastic bone formation were assessed using alkaline phosphatase, alizarin red S staining, and calcein-alizarin red S double labeling. Farrerol inhibited osteoclastogenesis and bone resorption in osteoclasts by suppressing nuclear factor kappa B signaling rather than mitogen-activated protein kinase signaling in vitro. Farrerol protected mice against ovariectomy-induced bone loss by inhibiting osteoclast-mediated bone resorption, instead of promoting osteoblast-mediated bone formation in vivo. The findings of the current study revealed that farrerol is a potential therapeutic agent for osteoporosis.

The miR-19a/Cylindromatosis Axis Regulates Pituitary Adenoma Bone Invasion by Promoting Osteoclast Differentiation

BACKGROUND

The presence of bone invasion in aggressive pituitary adenoma (PA) was found in our previous study, suggesting that PA cells may be involved in the process of osteoclastogenesis. miR-19a (as a key member of the miR-17-92 cluster) has been reported to activate the nuclear factor-кB (NF-кB) pathway and promote inflammation, which could be involved in the process of the bone invasion of pituitary adenoma.

METHODS

In this work, FISH was applied to detect miR-19a distribution in tissues from patients with PA. A model of bone invasion in PA was established, GH3 cells were transfected with miR-19a mimic, and the grade of osteoclastosis was detected by HE staining. qPCR was performed to determine the expression of miR-19a throughout the course of RANKL-induced osteoclastogenesis. After transfected with a miR-19a mimic, BMMs were treated with RANKL for the indicated time, and the osteoclast marker genes were detected by qPCR and Western Blot. Pit formation and F-actin ring assay were used to evaluate the function of osteoclast. The TargetScan database and GSEA were used to find the potential downstream of miR-19a, which was verified by Co-IP, Western Blot, and EMSA.

RESULTS

Here, we found that miR-19a expression levels were significantly correlated with the bone invasion of PA, both in clinical samples and animal models. The osteoclast formation prior to bone resorption was dramatically enhanced by miR-19, which was mediated by decreased cylindromatosis (CYLD) expression, increasing the K63 ubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6). Consequently, miR-19a promotes osteoclastogenesis by the activation of the downstream NF-кB and mitogen-activated protein kinase (MAPK) pathways.

CONCLUSIONS

To summarize, the results of this study indicate that PA-derived miR-19a promotes osteoclastogenesis by inhibiting CYLD expression and enhancing the activation of the NF-кB and MAPK pathways.

Morusin Inhibits RANKL-induced Osteoclastogenesis and Ovariectomized Osteoporosis

BACKGROUND

Postmenopausal osteoporosis (PMOP) is a classic type of osteoporosis that has gradually become a significant health problem worldwide. There is an urgent need for a safe alternative therapeutic agent considering the poor therapeutic strategies currently available for this disease. The roots and bark of the Morus australis tree (Moraceae) are used to make a traditional Chinese medicine known as "Morusin", and accumulating evidence has demonstrated its multiple activities, such as anti-inflammatory and anti-tumor effects.

OBJECTIVE

In this study, we aim to explore the effect of Morusin on mouse osteoclasts and its mechanism.

METHODS

In this study, we explored the inhibitory effects of Morusin on murine osteoclasts in vitro and its mechanism, and the protective effect of Morusin on an ovariectomy (OVX)-induced osteoporosis model in vivo.

RESULTS

The results showed that Morusin prevented OVX-induced bone loss and dramatically decreased RANKL-induced osteoclastogenesis. Morusin interfered with RANKL-activated NF- κB, MAPK, and PI3K/AKT signaling pathways. The expression of three master factors that control osteoclast differentiation, c-Fos, NFATc1, and c-Jun, was reduced by Morusin treatment. Collectively, in vitro results indicated that Morusin has a protective effect on OVX-induced bone loss in a mouse model.

CONCLUSION

Our data provide encouraging evidence that Morusin may be an effective treatment for PMOP.

Network based approach to identify interactions between Type 2 diabetes and cancer comorbidities

High blood sugar and insulin insensitivity causes the lifelong chronic metabolic disease called Type 2 diabetes (T2D) which has a higher chance of developing different malignancies. T2D with comorbidities like Cancers can make normal medications for those disorders more difficult. There may be a significant correlation between comorbidities and have an impact on one another's health. These associations may be due to a number of direct and indirect mechanisms. Such molecular mechanisms that underpin T2D and cancer are yet unknown. However, the large volumes of data available on these diseases allowed us to use analytical tools for uncovering their interrelated pathways. Here, we tried to present a system for investigating potential comorbidity relationships between T2D and Cancer disease by looking at the molecular processes involved, analyzing a huge number of freely accessible transcriptomic datasets of various disorders using bioinformatics. Using semantic similarity and gene set enrichment analysis, we created an informatics pipeline that evaluates and integrates Gene Ontology (GO), expression of genes, and biological process data. We discovered genes that are common in T2D and Cancer along with molecular pathways and GOs. We compared the top 200 Differentially Expressed Genes (DEGs) from each selected T2D and cancer dataset and found the most significant common genes. Among all the common genes 13 genes were found most frequent. We also found 4 common GO terms: GO:0000003, GO:0000122, GO:0000165, and GO:0000278 among all the common GO terms between T2d and different cancers. Using these genes and GO term semantic similarity, we calculated the distance between these two diseases. The semantic similarity results of our study showed a higher association of Liver Cancer (LiC), Breast Cancer (BreC), Colorectal Cancer (CC), and Bladder Cancer (BlaC) with T2D. Furthermore we found KIF4A, NUSAP1, CENPF, CCNB1, TOP2A, CCNB2, RRM2, HMMR, NDC80, NCAPG, and IGFBP5 common hub proteins among different cancers correlated to T2D. AGE-RAGE signaling pathway in diabetic complications, Osteoclast differentiation, TNF signaling pathway, IL-17 signaling pathway, p53 signaling pathway, MAPK signaling pathway, Human T-cell leukemia virus 1 infection, and Non-alcoholic fatty liver disease are the 8 most significant pathways found among 18 common pathways between T2D and selected cancers. As a result of our technique, we now know more about disease pathways that are critical between T2D and cancer.

Material matters: exploring the interplay between natural biomaterials and host immune system

Biomaterials are widely used for various medical purposes, for instance, implants, tissue engineering, medical devices, and drug delivery systems. Natural biomaterials can be obtained from proteins, carbohydrates, and cell-specific sources. However, when these biomaterials are introduced into the body, they trigger an immune response which may lead to rejection and failure of the implanted device or tissue. The immune system recognizes natural biomaterials as foreign substances and triggers the activation of several immune cells, for instance, macrophages, dendritic cells, and T cells. These cells release pro-inflammatory cytokines and chemokines, which recruit other immune cells to the implantation site. The activation of the immune system can lead to an inflammatory response, which can be beneficial or detrimental, depending on the type of natural biomaterial and the extent of the immune response. These biomaterials can also influence the immune response by modulating the behavior of immune cells. For example, biomaterials with specific surface properties, such as charge and hydrophobicity, can affect the activation and differentiation of immune cells. Additionally, biomaterials can be engineered to release immunomodulatory factors, such as anti-inflammatory cytokines, to promote a tolerogenic immune response. In conclusion, the interaction between biomaterials and the body's immune system is an intricate procedure with potential consequences for the effectiveness of therapeutics and medical devices. A better understanding of this interplay can help to design biomaterials that promote favorable immune responses and minimize adverse reactions.

Euonymus alatus (Thunb.) Siebold Prevents Osteoclast Differentiation and Osteoporosis

Euonymus alatus (Thunb.) Siebold, a traditional medicinal plant, has been used in China and several other Asian countries to address a variety of health concerns. The extensive research conducted on E. alatus is driven by its diverse pharmacological applications. However, its biological effects on osteoclastogenesis and osteoporosis have not been previously studied. In this research, we investigated the impact of an ethanolic extract of E. alatus (EEEA) on osteoclast differentiation and function as well as estrogen deficiency-induced bone loss. We found that EEEA inhibits osteoclast differentiation by downregulating the expression of the receptor activator of nuclear factor-κB ligand (RANKL) in osteoclast-supporting cells and by directly impeding RANKL-mediated signaling pathways for osteoclastogenesis in precursor cells. In addition, EEEA inhibited the bone-resorptive function of mature osteoclasts in vitro. Furthermore, oral administration of EEEA significantly alleviated bone loss in an ovariectomy-induced osteoporosis mouse model. Additionally, we identified phytochemicals in EEEA that have suppressive effects on osteoclast differentiation and bone loss. Collectively, these results suggest that EEEA holds potential as a biotherapeutic candidate for anti-postmenopausal osteoporosis.

Pharmacological options in the treatment of osteogenesis imperfecta: A comprehensive review of clinical and potential alternatives

Osteogenesis imperfecta (OI) is a genetically heterogeneous connective tissue disorder characterized by bone fragility and different extra-skeletal manifestations. The severity of these manifestations makes it possible to classify OI into different subtypes based on the main clinical features. This review aims to outline and describe the current pharmacological alternatives for treating OI, grounded on clinical and preclinical reports, such as antiresorptive agents, anabolic agents, growth hormone, and anti-TGFβ antibody, among other less used agents. The different options and their pharmacokinetic and pharmacodynamic properties will be reviewed and discussed, focusing on the variability of their response and the molecular mechanisms involved to attain the main clinical goals, which include decreasing fracture incidence, improving pain, and promoting growth, mobility, and functional independence.

ER Stress, the Unfolded Protein Response and Osteoclastogenesis: A Review

Endoplasmic reticulum (ER) stress and its adaptive mechanism, the unfolded protein response (UPR), are triggered by the accumulation of unfolded and misfolded proteins. During osteoclastogenesis, a large number of active proteins are synthesized. When an imbalance in the protein folding process occurs, it causes osteoclasts to trigger the UPR. This close association has led to the role of the UPR in osteoclastogenesis being increasingly explored. In recent years, several studies have reported the role of ER stress and UPR in osteoclastogenesis and bone resorption. Here, we reviewed the relevant literature and discussed the UPR signaling cascade response, osteoclastogenesis-related signaling pathways, and the role of UPR in osteoclastogenesis and bone resorption in detail. It was found that the UPR signal (PERK, CHOP, and IRE1-XBP1) promoted the expression of the receptor activator of the nuclear factor-kappa B ligand (RANKL) in osteoblasts and indirectly enhanced osteoclastogenesis. IRE1 promoted osteoclastogenesis via promoting NF-κB, MAPK signaling, or the release of pro-inflammatory factors (IL-6, IL-1β, and TNFα). CREBH promoted osteoclast differentiation by promoting NFATc1 expression. The PERK signaling pathway also promoted osteoclastogenesis through NF-κB and MAPK signaling pathways, autophagy, and RANKL secretion from osteoblasts. However, salubrinal (an inhibitor of eIF2α dephosphorylation that upregulated p-eIF2α expression) directly inhibited osteoclastogenesis by suppressing NFATc1 expression and indirectly promoted osteoclastogenesis by promoting RANKL secretion from osteoblasts. Therefore, the specific effects and mechanisms of p-PERK and its downstream signaling on osteoclastogenesis still need further experiments to confirm. In addition, the exact role of ATF6 and BiP in osteoclastogenesis also required further exploration. In conclusion, our detailed and systematic review provides some references for the next step to fully elucidate the relationship between UPR and osteoclastogenesis, intending to provide new insights for the treatment of diseases caused by osteoclast over-differentiation, such as osteoporosis.

Hedgehog signaling regulates bone homeostasis through orchestrating osteoclast differentiation and osteoclast-osteoblast coupling

Imbalance of bone homeostasis induces bone degenerative diseases such as osteoporosis. Hedgehog (Hh) signaling plays critical roles in regulating the development of limb and joint. However, its unique role in bone homeostasis remained largely unknown. Here, we found that canonical Hh signaling pathway was gradually augmented during osteoclast differentiation. Genetic inactivation of Hh signaling in osteoclasts, using Ctsk-Cre;Smof/f conditional knockout mice, disrupted both osteoclast formation and subsequent osteoclast-osteoblast coupling. Concordantly, either Hh signaling inhibitors or Smo/Gli2 knockdown stunted in vitro osteoclast formation. Mechanistically, Hh signaling positively regulated osteoclast differentiation via transactivation of Traf6 and stabilization of TRAF6 protein. Then, we identified connective tissue growth factor (CTGF) as an Hh-regulatory bone formation-stimulating factor derived from osteoclasts, whose loss played a causative role in osteopenia seen in CKO mice. In line with this, recombinant CTGF exerted mitigating effects against ovariectomy induced bone loss, supporting a potential extension of local rCTGF treatment to osteoporotic diseases. Collectively, our findings firstly demonstrate that Hh signaling, which dictates osteoclast differentiation and osteoclast-osteoblast coupling by regulating TRAF6 and CTGF, is crucial for maintaining bone homeostasis, shedding mechanistic and therapeutic insights into the realm of osteoporosis.

Methanolic extract of O.umbellata L. exhibits anti-osteoporotic effect via promoting osteoblast proliferation in MG-63 cells and inhibiting osteoclastogenesis in RANKL-stimulated RAW 264.7 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Oldenlandia umbellataL., belonging to the Rubiaceae family, is an annual plant possessing anti-inflammatory and antipyretic, anti-nociceptive, anti-bacterial, anti-helminthic, antioxidant and hepatoprotective activities and used in traditional medicine to treat inflammation and respiratory diseases.

AIM OF THE STUDY

The present study aims to evaluate the anti-osteoporotic effect of Methanolic extract of O.umbellata in MG-63 cells and RANKL-stimulated RAW 264.7 cells.

MATERIALS AND METHODS

The methanolic extract from the aerial parts of O.umbellata was subjected to metabolite profiling. The anti-osteoporotic effect of MOU was assessed in MG-63 cells and RANKL-stimulated RAW 264.7 cells. In MG-63 cells, the proliferative effect of MOU was evaluated using MTT assay, ALP assay, Alizarin red staining, ELISA and western blot. Similarly, the anti-osteoclastogenic effect of MOU was assessed in RANKL-stimulated RAW 264.7 cells via MTT, TRAP staining and western blot.

RESULTS

LC-MS metabolite profiling showed the presence of 59 phytoconstituents including scandoside, scandoside methyl ester, deacetylasperuloside, asperulosidic acid, and cedrelopsin in MOU. In MG-63 cells, MOU has increased the proliferation of osteoblast cells and ALP activity, thereby increasing bone mineralization. ELISA results showed increased levels of osteogenic markers such as osteocalcin and osteopontin in the culture media. Western blot analysis showed inhibition of GSK3β protein expression and increased the expression levels of β-catenin, Runx-2, col 1 and osterix, promoting osteoblast differentiation. In RANKL-stimulated RAW 264.7 cells, MOU did not elicit any significant cytotoxicity; instead, it suppressed the osteoclastogenesis reducing the osteoclast number. MOU has reduced TRAP activity in a dose-dependent manner. MOU inhibited the TRAF6, NFATc1, c-Jun, C-fos and cathepsin K expression, thereby inhibiting osteoclast formation.

CONCLUSION

In conclusion, MOU promoted osteoblast differentiation via inhibiting GSK3β and activating Wnt/β catenin signalling and its transcription factors, including β catenin, Runx2 and Osterix. Similarly, MOU inhibited osteoclast formation by inhibiting the expression of TRAF6, NFATc1, c-Jun, C-fos and cathepsin K in RANK-RANKL signalling. Finally, it can be emphasised that O.umbellata is a potential source of therapeutic leads for the treatment of osteoporosis.

Fine-tuning osteoclastogenesis: An insight into the cellular and molecular regulation of osteoclastogenesis

Osteoclasts, the bone-resorbing cells, are essential for the bone remodeling process and are involved in the pathophysiology of several bone-related diseases. The extensive corpus of in vitro research and crucial mouse model studies in the 1990s demonstrated the key roles of monocyte/macrophage colony-stimulating factor, receptor activator of nuclear factor kappa B ligand (RANKL) and integrin αvβ3 in osteoclast biology. Our knowledge of the molecular mechanisms by which these variables control osteoclast differentiation and function has significantly advanced in the first decade of this century. Recent developments have revealed a number of novel insights into the fundamental mechanisms governing the differentiation and functional activity of osteoclasts; however, these mechanisms have not yet been adequately documented. Thus, in the present review, we discuss various regulatory factors including local and hormonal factors, innate as well as adaptive immune cells, noncoding RNAs (ncRNAs), etc., in the molecular regulation of the intricate and tightly regulated process of osteoclastogenesis. ncRNAs have a critical role as epigenetic controllers of osteoclast physiologic activities, including differentiation and bone resorption. The primary ncRNAs, which include micro-RNAs, circular RNAs, and long noncoding RNAs, form a complex network that affects gene transcription activities associated with osteoclast biological activity. Greater knowledge of the involvement of ncRNAs in osteoclast biological activities will contribute to the treatment and management of several skeletal diseases such as osteoporosis, osteoarthritis, rheumatoid arthritis, etc. Moreover, we further outline potential therapies targeting these regulatory pathways of osteoclastogenesis in distinct bone pathologies.

Role of cathepsin D induced by Porphyromonas gingivalis lipopolysaccharide in periodontitis

Periodontitis is an inflammatory disease of tooth-supporting tissues caused by oral bacteria. Periodontal ligament loss and alveolar bone destruction occur in progressive periodontitis. Since gingival crevicular fluids (GCF) reflects the inflammatory environment of the periodontal pocket, it is a very important specimen for developing targets for periodontitis diagnosis. An antibody array was performed using GCF collected from healthy participants and patients with periodontitis to identify the proteolytic enzymes involved in periodontitis. Of 21 targets on the antibody array membrane, kallikrein 6 (KLK6), kallikrein 10 (KLK10), cathepsin A (CathA), and cathepsin D (CathD) showed higher levels in periodontitis GCF than in GCF from healthy participants. Lipopolysaccharide stimulation of Porphyromonas gingivalis (PG-LPS) in immortalized gingival fibroblasts only increased CathD protein levels among the four targets. The substrate cleavage activity of CathD was increased in PG-LPS-treated immortalized gingival fibroblast extract. The PG-LPS-induced substrate cleavage effect was abolished by the CathD inhibitor pepstatin A. Osteoclast formation was promoted by treatment with conditioned media from PG-LPS- treated immortalized gingival fibroblasts but inhibited by the CathD inhibitor pepstatin A. These results suggest that PG-LPS affected the osteoclast formation process by increasing CathD expression in cells around the alveolar bone, thereby participating in periodontitis progression.

Aspirin prevents estrogen deficiency-induced bone loss by inhibiting osteoclastogenesis and promoting osteogenesis

BACKGROUND

Aspirin is a commonly used antipyretic, analgesic, and anti-inflammatory drug. Numerous researches have demonstrated that aspirin exerts multiple biological effects on bone metabolism. However, its spatiotemporal roles remain controversial according to the specific therapeutic doses used for different clinical conditions, and the detailed mechanisms have not been fully elucidated. Hence, in the present study, we aimed to identify the dual effects of different aspirin dosages on osteoclastic activity and osteoblastic bone formation in vitro and in vivo.

METHODS

The effects of varying doses of aspirin on osteoclast and osteoblast differentiation were evaluated in vitro. The underlying molecular mechanisms were detected using quantitative real-time polymerase chain reaction, western blotting, and immunofluorescence techniques. An ovariectomized rat osteoporosis model was used to assess the bone-protective effects of aspirin in vivo.

RESULTS

Aspirin dose-dependently suppressed RANKL-induced osteoclasts differentiation and bone resorption in vitro and reduced the expression of osteoclastic marker genes, including TRAP, cathepsin K, and CTR. Further molecular analysis revealed that aspirin impaired the RANKL-induced NF-κB and MAPK signaling pathways and prevented the nuclear translocation of the NF-κB p65 subunit. Low-dose aspirin promoted osteogenic differentiation, whereas these effects were attenuated when high-dose aspirin was administered. Both low and high doses of aspirin prevented bone loss in an ovariectomized rat osteoporosis model in vivo.

CONCLUSION

Aspirin inhibits RANKL-induced osteoclastogenesis and promotes osteogenesis in a dual regulatory manner, thus preventing bone loss in vivo. These data indicate that aspirin has potential applications in the prevention and treatment of osteopenia.

RUNX2 promotes the suppression of osteoblast function and enhancement of osteoclast activity by multiple myeloma cells

RUNX2 is a transcription factor that participates in osteoblast differentiation and chondrocyte maturation and plays an important role in the invasion and metastasis of cancers. With the deepening of research, evidence has indicated the correlation between RUNX2 and bone destruction in cancers. However, the mechanisms underlying its role in multiple myeloma remain unclear. By observing the induction effects of conditioned medium from myeloma cells on preosteoblasts (MC3T3-E1) and preosteoclasts (RAW264.7) and constructing myeloma-bearing mice, we found that RUNX2 promotes bone destruction in multiple myeloma. In vitro, conditioned medium from RUNX2-overexpressing myeloma cells reduced osteoblast activity and increased osteoclast activity. In vivo, RUNX2 expression was positively correlated with bone loss in myeloma-bearing mice. These results suggest that therapeutic inhibition of RUNX2 may protect against bone destruction by maintaining the balance between osteoblast and osteoclast activity in multiple myeloma.

HSC70 mediated autophagic degradation of oxidized PRL2 is responsible for osteoclastogenesis and inflammatory bone destruction

Inflammation leads to systemic osteoporosis or local bone destruction, however, the underlying molecular mechanisms are still poorly understood. In this study, we report that PRL2 is a negative regulator of osteoclastogenesis and bone absorption. Mice with PRL2 deficiency exhibit a decrease in bone volume and an increase in osteoclast numbers. PRL2 negatively regulates RANKL-induced reactive oxygen species production through the activation of RAC1, thus PRL2 deficient osteoclast precursors have both increased osteoclast differentiation ability and bone resorptive capacity. During inflammation, oxidized PRL2 is a selected substrate of HSC70 and conditions of oxidative stress trigger rapid degradation of PRL2 by HSC70 mediated endosomal microautophagy and chaperone-mediated autophagy. Ablation of PRL2 in mouse models of inflammatory bone disease leads to an increase in the number of osteoclasts and exacerbation of bone damage. Moreover, reduced PRL2 protein levels in peripheral myeloid cells are highly correlated with bone destruction in a mouse arthritis model and in human rheumatoid arthritis, while the autophagy inhibitor hydroxychloroquine blocked inflammation-induced PRL2 degradation and bone destruction in vivo. Therefore, our findings identify PRL2 as a new regulator in osteoimmunity, providing a link between inflammation and osteoporosis. As such, PRL2 is a potential therapeutic target for inflammatory bone disease and inhibition of HSC70 mediated autophagic degradation of PRL2 may offer new therapeutic tools for the treatment of inflammatory bone disease.

(S)-2-(Cyclobutylamino)-N-(3-(3,4-dihydroisoquinolin-2(1H)-yl)-2-hydroxypropyl)isonicotinamide Attenuates RANKL-Induced Osteoclast Differentiation by Inhibiting NF-κB Nuclear Translocation

Osteoporosis is a common skeletal disease; however, effective pharmacological treatments still need to be discovered. This study aimed to identify new drug candidates for the treatment of osteoporosis. Here, we investigated the effect of EPZ compounds, protein arginine methyltransferase 5 (PRMT5) inhibitors, on RANKL-induced osteoclast differentiation via molecular mechanisms by in vitro experiments. EPZ015866 attenuated RANKL-induced osteoclast differentiation, and its inhibitory effect was more significant than EPZ015666. EPZ015866 suppressed the F-actin ring formation and bone resorption during osteoclastogenesis. In addition, EPZ015866 significantly decreased the protein expression of Cathepsin K, NFATc1, and PU.1 compared with the EPZ015666 group. Both EPZ compounds inhibited the nuclear translocation of NF-κB by inhibiting the dimethylation of the p65 subunit, which eventually prevented osteoclast differentiation and bone resorption. Hence, EPZ015866 may be a potential drug candidate for the treatment of osteoporosis.

Crucial Role of Lysine-Specific Histone Demethylase 1 in RANKL-Mediated Osteoclast Differentiation

Epigenetic regulators are involved in osteoclast differentiation. This study proposes that the inhibitors of epigenetic regulators could be effective in the treatment of osteoporosis. This study identified GSK2879552, a lysine-specific histone demethylase 1 (LSD1) inhibitor, as a candidate for the treatment of osteoporosis from epigenetic modulator inhibitors. We investigate the function of LSD1 during RANKL-induced osteoclast formation. LSD1 small-molecule inhibitors effectively inhibit the RANKL-induced osteoclast differentiation in a dose-dependent manner. LSD1 gene knockout in macrophage cell line Raw 264.7 also inhibits RANKL-mediated osteoclastogenesis. LSD1-inhibitor-treated primary macrophage cells and LSD1 gene knockout Raw 264.7 cells failed to show actin ring formation. LSD1 inhibitors prevent the expression of RANKL-induced osteoclast-specific genes. They also downregulated the protein expression of osteoclast-related markers in osteoclastogeneses, such as Cathepsin K, c-Src, and NFATc1. Although LSD1 inhibitors were shown to reduce the in vitro demethylation activity of LSD1, they did not modulate the methylation of Histone 3 K4 and K9 during osteoclastogenesis. The ovariectomy (OVX)-induced osteoporosis model revealed that GSK2879552 slightly restores OVX-induced cortical bone loss. LSD1 can be employed as a positive regulator to promote osteoclast formation. Hence, inhibition of LSD1 activities is a potential target for preventing bone diseases characterized by excessive osteoclast activities.

Small molecule inhibitors of osteoarthritis: Current development and future perspective

Osteoarthritis (OA) is one of the common degenerative joint diseases in clinic. It mainly damages articular cartilage, causing pain, swelling and stiffness around joints, and is the main cause of disability of the elderly. Due to the unclear pathogenesis of osteoarthritis and the poor self-healing ability of articular cartilage, the treatment options for this disease are limited. At present, NSAIDs, Glucocorticoid and Duloxetine are the most commonly used treatment choice for osteoarthritis. Although it is somewhat effective, the adverse reactions are frequent and serious. The development of safer and more effective anti-osteoarthritis drugs is essential and urgent. This review summarizes recent advances in the pharmacological treatment of OA, focusing on small molecule inhibitors targeting cartilage remodeling in osteoarthritis as well as the research idea of reducing adverse effects by optimizing the dosage form of traditional drugs for the treatment of osteoarthritis. It should provide a reference for exploration of new potential treatment options.

HSP90 drives the Rab11a-mediated vesicular transport of the cell surface receptors in osteoclasts

Rab11a, which ubiquitously localizes to early and recycling endosomes, is required for regulating the vesicular transport of cellular cargos. Interestingly, our previous study revealed that Rab11a served as a negative regulator of osteoclastogenesis by facilitating the lysosomal proteolysis of (1) colony-stimulating factor-1 (c-fms) receptor and (2) receptor activator of nuclear factor-κB (RANK) receptor, thereby resulting in inhibition of osteoclast (OC) differentiation, maturation, and bone-resorbing activity. However, the molecular mechanisms of how Rab11a negatively affected osteoclastogenesis were largely unknown. Heat shock protein (HSP90), including two isoforms HSP90α and HSP90β, necessitates the stability, maturation, and activity of a broad range of its clients, and is essentially required for a vast array of signal transduction pathways in nonstressful conditions. Furthermore, cumulative evidence suggests that HSP90 is a vital element of the vesicular transport network. Indeed, our recent study revealed that HSP90, a novel effector protein of Rab11b, modulated Rab11b-mediated osteoclastogenesis. In this study, we also found that Rab11a interacted with both HSP90α and HSP90β in OCs. Upon blockade of HSP90 ATPase activity by a specific inhibitor(17-allylamino-demethoxygeldanamycin), we showed that (1) the ATPase domain of HSP90 was a prerequisite for the interaction between HSP90 and Rab11a, and (2) the interaction of HSP90 to Rab11a sufficiently maintained the inhibitory effects of Rab11a on osteoclastogenesis. Altogether, our findings undoubtedly indicate a novel role of HSP90 in regulating Rab11a-mediated osteoclastogenesis.

Lophatherum gracile Bronghiart Suppresses Receptor Activator of Nuclear Factor Kappa-B Ligand-Stimulated Osteoclastogenesis and Prevents Ovariectomy-Induced Osteoporosis

Lophatherum gracile Bronghiart, used in traditional herbal medicine, has many biological properties including antiviral, antipyretic, antitumor, vasorelaxation, and neutrophilic inflammatory effects. However, its modulatory effects on bone metabolism have not been investigated previously. In this study, we examined the effects of a water extract of the leaves of L. gracile (WELG) on osteoclast differentiation and bone loss, and explored its underlying mechanisms. We found that WELG inhibits osteoclastogenesis by suppressing both receptor activator of nuclear factor-κB ligand (RANKL)-induced early activation of mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB)- and RANKL-induced modulation of the positive and negative regulators of osteoclastogenesis in osteoclast precursors. In vivo study demonstrated that WELG protects against bone loss, weight gain, and fat accumulation without affecting uterine atrophy in an ovariectomy-induced postmenopausal osteoporosis mice model. In addition, photochemical analysis of WELG identified active constituents known to have bone-protective effects. Overall, the results of this study suggest that WELG can be a potential candidate for therapy and prevention of postmenopausal osteoporosis.

A Review of Signaling Transduction Mechanisms in Osteoclastogenesis Regulation by Autophagy, Inflammation, and Immunity

Osteoclastogenesis is an ongoing rigorous course that includes osteoclast precursors fusion and bone resorption executed by degradative enzymes. Osteoclastogenesis is controlled by endogenous signaling and/or regulators or affected by exogenous conditions and can also be controlled both internally and externally. More evidence indicates that autophagy, inflammation, and immunity are closely related to osteoclastogenesis and involve multiple intracellular organelles (e.g., lysosomes and autophagosomes) and certain inflammatory or immunological factors. Based on the literature on osteoclastogenesis induced by different regulatory aspects, emerging basic cross-studies have reported the emerging disquisitive orientation for osteoclast differentiation and function. In this review, we summarize the partial potential therapeutic targets for osteoclast differentiation and function, including the signaling pathways and various cellular processes.

Inhibitory Effect of Biotransformed-Fucoidan on the Differentiation of Osteoclasts Induced by Receptor for Activation of Nuclear Factor-κB Ligand

Bone homeostasis is regulated by constant remodeling through osteogenesis by osteoblasts and osteolysis by osteoclasts and osteoporosis can be provoked when this balance is broken. Present pharmaceutical treatments for osteoporosis have harmful side effects and thus, our goal was to develop therapeutics from intrisincally safe natural products. Fucoidan is a polysaccharide extracted from many species of brown seaweed, with valuable pharmaceutical activities. To intensify the effect of fucoidan on bone homeostasis, we hydrolyzed fucoidan using AMG, Pectinex and Viscozyme. Of these, fucoidan biotransformed by Pectinex (Fu/Pec) powerfully inhibited the induction of tartrate-resistant acid phosphatase (TRAP) activity in osteoclasts differentiated from bone marrow macrophages (BMMs) by the receptor for activation of nuclear factor-κB ligand (RANKL). To investigate potential of lower molecular weight fucoidan it was separated into >300 kDa, 50-300 kDa, and <50 kDa Fu/Pec fractions by ultrafiltration system. The effects of these fractions on TRAP and alkaline phosphatase (ALP) activities were then examined in differentiated osteoclasts and MC3T3-E1 osteoblasts, respectively. Interestingly, 50-300 kDa Fu/Pec suppressed RANKL-induced osteoclasts differentiation from BMMs but did not synergistically enhance osteoblasts differentiation induced by osteogenic agents. In addition, this fraction inhibited the expressions of NFATc1, TRAP, OSCAR, and RANK, which are all key transcriptional factors involved in osteoclast differentiation, and those of Src, c-Fos and Mitf, as determined by RT-PCR. In conclusion, enzymatically low-molecularized 50-300 kDa Fu/Pec suppressed TRAP by downregulating RANKL-related signaling, contributing to the inhibition of osteoclasts differentiation, and represented a potential means of inducing bone remodeling in the background of osteoporosis.

How zoledronic acid improves osteoporosis by acting on osteoclasts

Osteoporosis is called a silent disease, because it is difficult to detect until comprehensive examinations for osteoporosis are performed or osteoporotic fractures occur. Zoledronic acid is currently the first-line anti-osteoporotic drug, with good efficacy and treatment compliance. A major advantage of zoledronic acid is that intravenous zoledronic acid often guarantees a therapeutic effect for up to 1 year after infusion. The reasons why zoledronic acid is effective in improving osteoporosis are that it can inhibit osteoclast differentiation and induce osteoclast apoptosis, thus suppressing bone resorption and increasing bone density. The story between zoledronic acid and osteoclasts has been written long time ago. Both the canonical receptor activator of the receptor activator of nuclear factor-κB ligand (RANKL) pathway and the non-canonical Wnt pathway are the main pathways by which zoledronic acid inhibits osteoclast differentiation. Farnesyl pyrophosphate synthase (FPPS), reactive oxygen species (ROS), and ferroptosis that was first proposed in 2012, are all considered to be closely associated with zoledronic acid-induced osteoclast apoptosis. Here, we provide a brief review of the recent progress on the study of zoledronic acid and osteoclasts, and hope to elaborate how zoledronic acid improves osteoporosis by acting on osteoclasts.

Loureirin B downregulates osteoclast differentiation of bone marrow macrophages by targeting the MAPK signaling pathway

Excessive absorption of osteoclasts will break the balance between osteoclasts and osteoblasts, leading to bone loss, decreased bone density, and increased bone fragility. We have shown that Loureirin B (LrB) can inhibit osteoclasts. In this study, we demonstrated the targeting-inhibitory mechanism of LrB acting on osteoclast precursor. Using SPR, HPLC and MALDI-TOF-MS to capture and analyze the target protein of Loureirin B in bone marrow macrophages (BMMs), we used this method to detect all target proteins that LrB acts on BMMs, and analyzed the distribution and enrichment rate of the target protein by DAVID enrichment analysis. Ledock molecular docking was used to detect the binding of LrB. We used Western Blot for verification. The target proteins of LrB acting on BMMs were Serpine1, Atp6ap1, Dvl1, Rhd, Fzd2, MAPK1, MAP2K2, MAPK3 and so on. MAPK1, MAP2K2 and MAPK3 were the most relevant. LrB treatment attenuated the expression of phosphorylated JNK and p38 kinases of the MAPK signaling pathway. Our research further confirmed that LrB affects the MAPK signaling pathway in BMMs, thereby inhibiting the differentiation of BMMs into osteoclasts. This discovery can confirm the mechanism by which LrB acts on BMMs.

Blockade of Osteoclast-Mediated Bone Resorption With a RANKL-Inhibitor Enhances Bone Formation in a Rat Spinal Fusion Model

STUDY DESIGN

Rat spine fusion model.

OBJECTIVE

The present study aimed to determine whether administration of osteoprotegerin (OPG) in a rat model of spinal fusion increases bone volume, bone density, and decreases osteoclasts in the fusion mass.

SUMMARY OF BACKGROUND DATA

OPG is a soluble RANK-ligand inhibitor that blocks osteoclast differentiation and activation. This makes it a potential agent to control the remodeling process and enhance bone mass during spinal fusion.

MATERIALS AND METHODS

Forty-eight male Sprague-Dawley rats received a one-level spinal fusion of L4-L5 with bone allograft. Rats were then divided into four groups according to initiation of treatment: (1) saline on day 0 (saline), (2) OPG on day 0 (OPG D0), (3) OPG on day 10 (OPG D10), and (4) OPG on day 21 (OPG D21) postsurgery. After their initial injection, rats received weekly subcutaneous injections of OPG (10 mg/kg) and were euthanized six weeks postsurgery. MicroCT analysis of the fusion site and histological analysis of bone surface for quantification of osteoclast lining was performed.

RESULTS

Increased bone volume in the fusion site and around the spinous process was seen in OPG D0 and OPG D10 when compared with saline. Mean trabecular thickness was greater in all groups receiving OPG compared with saline, with OPG D0 and OPG D10 having significantly greater mean trabecular thickness than OPG D21. All OPG groups had less bone surface lined with osteoclasts when compared with Saline, with OPG D0 and OPG D10 having fewer than OPG D21.

CONCLUSIONS

This study indicates that OPG inhibited osteoclast bone resorption, which led to greater bone at the fusion site. Future studies investigating OPG on its own or in combination with an osteogenic factor to improve spinal fusion outcomes are warranted to further elucidate its potential therapeutic effect.

Isoliensinine Suppresses Osteoclast Formation Through NF-κB Signaling Pathways and Relieves Ovariectomy-Induced Bone Loss

Osteoporosis is among the major contributors of pathologic fracture in postmenopausal women, which is caused by the bone metabolic disorder owing to the over-activation of osteoclasts. Inhibition of osteoclast differentiation and maturation has become a mainstream research interest in the prevention of osteoporosis. Isoliensinine (Iso) is a dibenzyl isoquinoline alkaloid with antioxidant, anti-inflammatory, and anti-cancer activities. However, whether it can be used as a potential treatment for osteoporosis remains undiscovered. Here, we investigated whether Iso might suppress the differentiation of osteoclasts in vitro and in vivo to play an anti-osteoporosis role. Our results showed that Iso inhibits the formation of mature multinuclear osteoclasts induced by RANKL, the bone resorption, and the osteoclast-specific genes expression by blocking the nuclear translocation of NF-κB p65, and the effect was in a dosage-dependent way. Furthermore, we investigated the therapeutic effect of Iso on osteoporosis in ovariectomized (OVX) mice. We found that Iso attenuated bone loss in the OVX mice and significantly promoted BS, Conn. DN, Tb.Th, TB.N, and BV/TV Index. All in all, Iso showed a prominent effect of osteoclast inhibition, with great promise for treating osteoporosis.

Criteria, Challenges, and Opportunities for Acellularized Allogeneic/Xenogeneic Bone Grafts in Bone Repairing

As bone grafts become more commonly needed by patients and as donors become scarcer, acellularized bone grafts (ABGs) are becoming more popular for restorative purposes. While autogeneic grafts are reliable as a gold standard, allogeneic and xenogeneic ABGs have been shown to be of particular interest due to the limited availability of autogeneic resources and reduced patient well-being in long-term surgeries. Because of the complete similarity of their structures with native bone, excellent mechanical properties, high biocompatibility, and similarities of biological behaviors (osteoinductive and osteoconductive) with local bones, successful outcomes of allogeneic and xenogeneic ABGs in both in vitro and in vivo research have raised hopes of repairing patients' bone injuries in clinical applications. However, clinical trials have been delayed due to a lack of standardized protocols pertaining to acellularization, cell seeding, maintenance, and diversity of ABG evaluation criteria. This study sought to uncover these factors by exploring the bone structures, ossification properties of ABGs, sources, benefits, and challenges of acellularization approaches (physical, chemical, and enzymatic), cell loading, and type of cells used and effects of each of the above items on the regenerative technologies. To gain a perspective on the repair and commercialization of products before implementing new research activities, this study describes the differences between ABGs created by various techniques and methods applied to them. With a comprehensive understanding of ABG behavior, future research focused on treating bone defects could provide a better way to combine the treatment approaches needed to treat bone defects.

Silencing Itch in human peripheral blood monocytes promotes their differentiation into osteoclasts

Introduction

Two clinical case reports of humans with mutations in Itch reported distinct morphological defects such as stunted growth, macrocephaly, and dysmorphic features indicating a role for Itch in bone remodelling. Studies in mice have found that the encoded E3 ubiquitin ligase acts as a negative regulator of osteoclastogenesis, however no studies have investigated whether this is translatable to a human model.

Experimental procedures

Human peripheral blood monocytes were separated from whole blood and grown in M-CSF containing media. Media was later supplemented with RANKL to promote osteoclast differentiation. Transient siRNA-mediated Itch knockdown (si-Itch) in monocytes was verified by qPCR and western blot to confirm reduction in both Itch mRNA and protein respectively. Monocytes were aliquoted onto 96-well plates where confluence and osteoclast formation were analysed using automated cytometry analysis before and after staining for tartrate resistant acid phosphatase activity (TRAP). Cells were also stained with Hoechst33342 to look for multinucleate cells.

Results

Cells treated with si-Itch showed an 80% knockdown in Itch mRNA and > 75% reduction in protein. Following the 7-day differentiation period, si-Itch caused a 47% increase in multinucleate cells and a 17% increase in numbers of large cellular bodies and, indicating an overall increase in mature osteoclast formation.

Conclusions

Our preliminary data shows silencing Itch expression increases the potential of primary human monocytes to differentiate into osteoclast-like cells in vitro.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11033-022-07726-1.

IFT80 negatively regulates osteoclast differentiation via association with Cbl-b to disrupt TRAF6 stabilization and activation

Osteoclasts (OCs) are the sole bone resorbing cells indispensable for bone remodeling. Hence, understanding of novel signaling modulators regulating OC formation is clinically important. Intraflagellar transport (IFT) proteins are important for cilia, cell signaling, and organ development. It remains unclear whether IFT80 plays a role in OCs. This study uncovers an intriguing role of IFT80 in OCs where the ciliary protein regulates the stability of critical OC factor TRAF6 via Cbl-b and thereby contributes to the maintenance of OC numbers. These findings provide further basis for understanding and delineating the role of IFT proteins in OCs that may provide new strategies for treatment of osteolytic diseases.

Excess bone loss due to increased osteoclastogenesis is a significant clinical problem. Intraflagellar transport (IFT) proteins have been reported to regulate cell growth and differentiation. The role of IFT80, an IFT complex B protein, in osteoclasts (OCs) is completely unknown. Here, we demonstrate that deletion of IFT80 in the myeloid lineage led to increased OC formation and activity accompanied by severe bone loss in mice. IFT80 regulated OC formation by associating with Casitas B-lineage lymphoma proto-oncogene-b (Cbl-b) to promote protein stabilization and proteasomal degradation of tumor necrosis factor (TNF) receptor–associated factor 6 (TRAF6). IFT80 knockdown resulted in increased ubiquitination of Cbl-b and higher TRAF6 levels, thereby hyperactivating the receptor activator of nuclear factor-κβ (NF-κβ) ligand (RANKL) signaling axis and increased OC formation. Ectopic overexpression of IFT80 rescued osteolysis in a calvarial model of bone loss. We have thus identified a negative function of IFT80 in OCs.

Genkwanin Prevents Lipopolysaccharide-Induced Inflammatory Bone Destruction and Ovariectomy-Induced Bone Loss

Objectives

The first objective of this study was to probe the effects of genkwanin (GKA) on osteoclast. The second goal of this study was to study whether GKA can protect lipopolysaccharide (LPS) and ovariectomized (OVX) induced bone loss.

Materials and Methods

Various concentrations of GKA (1 and 10 mg/kg) were injected into mice. Different concentrations of GKA (1 and 5 μM) were used to detect the effects of GKA on osteoclast and osteoblast.

Key Findings

GKA attenuated the osteoclast differentiation promoted by RANKL and expression of marker genes containing c-fos, ctsk as well as bone resorption related gene Trap and to the suppression of MAPK signaling pathway. In addition, GKA induced BMMs cell apoptosis in vitro. Moreover, GKA prevented LPS-induced and ovariectomized-induced bone loss in mice.

Conclusion

Our research revealed that GKA had a potential to be an effective therapeutic agent for osteoclast-mediated osteoporosis.

SHIP1 Activator AQX-1125 Regulates Osteogenesis and Osteoclastogenesis Through PI3K/Akt and NF-κb Signaling

With the worldwide aging population, the prevalence of osteoporosis is on the rise, particularly the number of postmenopausal women with the condition. However, the various adverse side effects associated with the currently available treatment options underscore the need to develop novel therapies. In this study, we investigated the use of AQX-1125, a novel clinical-stage activator of inositol phosphatase-1 (SHIP1), in ovariectomized (OVX) mice, identifying a protective role. We then found that the effect was likely due to increased osteogenesis and mineralization and decreased osteoclastogenesis caused by AQX-1125 in a time- and dose-dependent manner. The effect against OVX-induced bone loss was identified to be SHIP1-dependent as pretreatment of BMSCs and BMMs with SHIP1 RNAi could greatly diminish the osteoprotective effects. Furthermore, SHIP1 RNAi administration in vivo induced significant bone loss and decreased bone mass. Mechanistically, AQX-1125 upregulated the expression level and activity of SHIP1, followed upregulating the phosphorylation levels of PI3K and Akt to promote osteoblast-related gene expressions, including Alp, cbfa1, Col1a1, and osteocalcin (OCN). NF-κB signaling was also inhibited through suppression of the phosphorylation of IκBα and P65 induced by RANKL, resulting in diminished osteoclastogenesis. Taken together, our results demonstrate that AQX-1125 may be a promising candidate for preventing and treating bone loss.

Evaluation of the anti-osteoporotic effect of a low-phenylalanine whey protein hydrolysate in an ovariectomized mice model

A phenylalanine (Phe)-restricted diet is indispensable to control the blood Phe for individuals with phenylketonuria (PKU), who are also confronted with progressive bone impairment. Thus, the development of a low-Phe protein substitute that could positively regulate bone metabolism is desired for their bone health. Our previous study reported the preparation of a low-Phe containing whey hydrolysate (LPH) from a selected whey protein hydrolysate (TAH). However, the effect of LPH on the bone status is unknown. In this study, we used an ovariectomized (OVX) mice model to evaluate the anti-osteoporotic potential of oral administration of whey protein concentrate (WPC, protein control), TAH, and LPH on bone physiology and bone metabolism. The results showed that after 12 weeks of treatment, the decreased bone mineral density, the deteriorated trabecular microarchitecture, and the reduced ultimate load due to ovariectomy were significantly attenuated by two whey protein hydrolysates (TAH and LPH); meanwhile, the body weight, uterine weight, bone composition, and the femoral elastic load of OVX mice had not been significantly affected by whey samples. In addition, LPH and TAH dual-regulated bone remodeling in OVX mice through triggering osteogenesis (promoted the expression of runt-related protein 2 (Runx2) and osteoformation markers) and inhibiting osteoresorption as well as inflammation. The modulated mitogen-activated protein kinase signaling and the inhibited nuclear factor κB signaling by LPH and TAH might relate to the dual-regulatory activities on bone. Overall, in the OVX mice model, LPH exerted higher osteoprotective potential than TAH of the same dose by activating the bone formation markers and inhibiting the inflammatory status. The current study demonstrated for the first time the potential use of a low-Phe whey hydrolysate, a protein substitute for PKU individuals, in the prevention of osteoporosis.

Rab34 plays a critical role as a bidirectional regulator of osteoclastogenesis

Accumulating evidence suggests that Rab GTPases representing the largest branch of Ras superfamily have recently emerged as the core factors for the regulation of osteoclastogenesis through modulating vesicular transport amongst specific subcellular compartments. Among these, Rab34 GTPase has been identified to be important for the post-Golgi secretory pathway and for phagocytosis; nevertheless, its specific role in osteoclastogenesis has been completely obscure. Here, upon the in vitro model of osteoclast formation derived from murine macrophages like RAW-D cells or bone marrow-derived macrophages, we reveal that Rab34 regulates osteoclastogenesis bidirectionally. More specifically, Rab34 serves as a negative regulator of osteoclast differentiation by promoting the lysosome-induced proteolysis of two osteoclastogenic surface receptors, c-fms and RANK, via the axis of early endosomes-late endosomes-lysosomes, leading to alleviate the transcriptional activity of two of the master regulator of osteoclast differentiation, c-fos and NFATc-1, eventually attenuating osteoclast differentiation and bone resorption. Besides, Rab34 plays a crucial role in modulating the secretory network of lysosome-related proteases including matrix metalloprotease 9 and Cathepsin K across the ruffled borders of osteoclasts, contributing to the regulation of bone resorption.

Anti-Osteoporosis Effect of Perilla frutescens Leaf Hexane Fraction through Regulating Osteoclast and Osteoblast Differentiation

Osteoporosis is the result of an imbalance in the bone-remodeling process via an increase in osteoclastic activity and a decrease in osteoblastic activity. Our previous studies have shown that Perilla frutescens seed meal has anti-osteoclastogenic activity. However, the role of perilla leaf hexane fraction (PLH) in osteoporosis has not yet been investigated and reported. In this study, we aimed to investigate the effects of PLH in osteoclast differentiation and osteogenic potential using cell-based experiments in vitro. From HPLC analysis, we found that PLH contained high luteolin and baicalein. PLH was shown to inhibit RANKL-induced ROS production and tartrate-resistant acid phosphatase (TRAP)-positive multi-nucleated osteoclasts. Moreover, PLH significantly downregulated the RANKL-induced MAPK and NF-κB signaling pathways, leading to the attenuation of NFATc1 and MMP-9 expression. In contrast, PLH enhanced osteoblast function by regulating alkaline phosphatase (ALP) and restoring TNF-α-suppressed osteoblast proliferation and osteogenic potential. Thus, luteolin and baicalein-rich PLH inhibits osteoclast differentiation but promotes the function of osteoblasts. Collectively, our data provide new evidence that suggests that PLH may be a valuable anti-osteoporosis agent.

Therapeutic Treatments for Osteoporosis-Which Combination of Pills Is the Best among the Bad?

Osteoporosis is a chronical, systemic skeletal disorder characterized by an increase in bone resorption, which leads to reduced bone density. The reduction in bone mineral density and therefore low bone mass results in an increased risk of fractures. Osteoporosis is caused by an imbalance in the normally strictly regulated bone homeostasis. This imbalance is caused by overactive bone-resorbing osteoclasts, while bone-synthesizing osteoblasts do not compensate for this. In this review, the mechanism is presented, underlined by in vitro and animal models to investigate this imbalance as well as the current status of clinical trials. Furthermore, new therapeutic strategies for osteoporosis are presented, such as anabolic treatments and catabolic treatments and treatments using biomaterials and biomolecules. Another focus is on new combination therapies with multiple drugs which are currently considered more beneficial for the treatment of osteoporosis than monotherapies. Taken together, this review starts with an overview and ends with the newest approaches for osteoporosis therapies and a future perspective not presented so far.

RAS protein activator like 2 promotes the proliferation and migration of pulmonary artery smooth muscle cell through AKT/mammalian target of Rapamycin complex 1 pathway in pulmonary hypertension

RAS protein activator like 2 (Rasal2) exerts pro-proliferative effect in several types of cells. However, whether Rasal2 is involved in the regulation of pulmonary artery smooth muscle cell (PASMC) remains unclear. In the current study, we explored the role of Rasal2 in proliferation and migration of PASMC during the development of pulmonary arterial hypertension (PAH). We found that the protein level of Rasal2 was increased in both pulmonary arteries of chronic hypoxia-induced pulmonary hypertension (CH-PH) mice and hypoxia-challenged PASMC. Overexpression of Rasal2 caused enhanced proliferation and migration of PASMC after hypoxia exposure. Mechanistically, we found elevated phosphorylation of AKT and two downstream effectors of mammalian target of Rapamycin complex 1 (mTORC1), S6 and 4E-Binding Protein 1 (4EBP1) after Rasal2 overexpression in hypoxia-challenged PASMC. Inactivation of mTORC1 abolished Rasal2-mediated enhancement of proliferation and migration of PASMC. Furthermore, we also demonstrated that AKT might act downstream of Rasal2 to enhance the activity of mTORC1. Once AKT was inactivated by MK-2206 application, overexpression of Rasal2 failed to further increase the phosphorylation level of S6 and 4EBP1. Finally, inhibition of AKT also blocked Rasal2-induced proliferation and migration in hypoxia-challenged PASMC. In conclusion, Rasal2 promotes the proliferation and migration of PASMC during the development of PAH via AKT/mTORC1 pathway.

Differentiation of Cells Isolated from Human Femoral Heads into Functional Osteoclasts

Proper formation of the skeleton during development is crucial for the mobility of humans and the maintenance of essential organs. The production of bone is regulated by osteoblasts and osteoclasts. An imbalance of these cells can lead to a decrease in bone mineral density, which leads to fractures. While many studies are emerging to understand the role of osteoblasts, less studies are present about the role of osteoclasts. This present study utilized bone marrow cells isolated directly from the bone marrow of femoral heads obtained from osteoarthritic (OA) patients after undergoing hip replacement surgery. Here, we used tartrate resistant acid phosphatase (TRAP) staining, Cathepsin K, and nuclei to identity osteoclasts and their functionality after stimulation with macrophage-colony stimulation factor (M-CSF) and receptor activator of nuclear factor kappa-β ligand (RANKL). Our data demonstrated that isolated cells can be differentiated into functional osteoclasts, as indicated by the 92% and 83% of cells that stained positive for TRAP and Cathepsin K, respectively. Furthermore, isolated cells remain viable and terminally differentiate into osteoclasts when stimulated with RANKL. These data demonstrate that cells isolated from human femoral heads can be differentiated into osteoclasts to study bone disorders during development and adulthood.

Exploring the potential therapeutic effect of Eucommia ulmoides–Dipsaci Radix herbal pair on osteoporosis based on network pharmacology and molecular docking technology

Eucommia ulmoides–Dipsaci Radix (EU–DR) is a commonly used herbal pair for the treatment of osteoporosis (OP) in China. The purpose of this study was to investigate the potential mechanism of EU–DR on OP through network pharmacology and molecular docking approaches. Combining data from multiple open-source databases and literature mining, the active compounds and potential targets of EU–DR were screened out. The OP related targets were identified from the interactive web tool GEO2R. The shared targets were obtained by intersecting the targets of EU–DR and OP. The protein–protein interaction (PPI) network was constructed via the STRING database and Cytoscape 3.7.2 software. GO and KEGG enrichment analysis were conducted using R 3.6.3 software with adjusted p-value < 0.05. Sybyl-x 2.1.1 and Autodock Vina 1.1.2 software were used to cross validate the affinity between active compounds and target proteins. Our results showed that a total of 50 active compounds were screened, corresponding to 895 EU–DR targets, 2202 OP targets and 144 shared targets. The flavonoids in EU–DR played an important role in anti-OP. The enrichment analysis of GO and KEGG suggested EU–DR exerted a therapeutic effect on OP mainly by regulating the osteoclast differentiation related signaling pathway. Meanwhile, molecular docking results showed that most active compounds in EU–DR had strong binding efficiency to the target proteins. In conclusion, this study elaborated the multi-component, multi-target, and multi-pathway interaction mechanism of the EU–DR herbal pair in the treatment of OP for the first time, which also provided a pharmacological basis for treating OP.

This study elaborated the multi-component, multi-target, and multi-pathway interaction mechanism of Eucommia ulmoides-Dipsaci Radix herbal pair in the treatment of osteoporosis.

Foxf1 gene increases the risk of osteoporosis in rats by inhibiting osteoblast formation and promoting osteoclast differentiation through the upregulation of NF-κB pathway

OBJECTIVES

a) To explore the expression of Foxf1 and NF-κB in bone tissue of ovariectomized rats with osteoporosis and b) to investigate the role and mechanism of NF-κB pathway regulated by Foxf1 gene in the differentiation and formation of rat osteoclasts and osteoblasts with cell experiments.

METHODS

Ovariectomized rat model of osteoporosis was established with 3-month-old female SD rats. The rats were divided into sham group (n=10) and osteoporosis group (n=10). Real time fluorescent quantitative PCR and Western blot were used to detect the expression levels of Foxf1 and NF-κB genes and proteins in the femur tissues of rats and analyze their correlation.

RESULTS

Both Foxf1 and NF- κB were highly expressed in the femur tissues. Upon the overexpression of Foxf1 gene in osteoblasts and osteoclasts in vitro, the gene and protein expression of NF-κB were also upregulated, significantly reducing the gene and protein expression levels of osteogenic factors, including ATF4, OCN, ALP and Runx2.

CONCLUSIONS

Foxf1 gene could inhibit osteoblast formation and promote osteoclast differentiation by NF-κB pathway, which may increase the risk of osteoporosis in rats.

Focusing on OB-OC-MΦ Axis and miR-23a to Explore the Pathogenesis and Treatment Strategy of Osteoporosis

Osteoporosis is a bone metabolic disorder characterized by decreased bone density and deteriorated microstructure, which increases the risk of fractures. The imbalance between bone formation and bone resorption results in the occurrence and progression of osteoporosis. Osteoblast-mediated bone formation, osteoclast-mediated bone resorption and macrophage-regulated inflammatory response play a central role in the process of bone remodeling, which together maintain the balance of the osteoblast-osteoclast-macrophage (OB-OC-MΦ) axis under physiological conditions. Bone formation and bone resorption disorders caused by the imbalance of OB-OC-MΦ axis contribute to osteoporosis. Many microRNAs are involved in the regulation of OB-OC-MΦ axis homeostasis, with microRNA-23a (miR-23a) being particularly crucial. MiR-23a is highly expressed in the pathological process of osteoporosis, which eventually leads to the occurrence and further progression of osteoporosis by inhibiting osteogenesis, promoting bone resorption and inflammatory polarization of macrophages. This review focuses on the role and mechanism of miR-23a in regulating the OB-OC-MΦ axis to provide new clinical strategies for the prevention and treatment of osteoporosis.

Gallic acid inhibits osteoclastogenesis and prevents ovariectomy-induced bone loss

Osteoporosis is a common metabolic bone disease with a rapidly increasing prevalence, characterized by massive bone loss because of excessive osteoclast formation. Gallic acid (GA), a phenolic acid isolated from Cornus officinalis, has anti-inflammatory and anti-oxidant effects, but its effect on osteoclast formation has not been confirmed. In our study, we demonstrated that GA significantly inhibited RANKL-induced osteoclast formation and function of osteoclast in bone marrow monocytes (BMMs) and RAW264.7 cells in a dose-dependent manner without cytotoxicity. For molecular mechanisms, GA repressed osteoclastogenesis by blocking Akt, ERK, and JNK pathways, and suppressed osteoclastogenesis-related marker expression, including nuclear factor of the activated T-cell cytoplasmic 1 (NFATc1), c-Fos, and cathepsin K (CTSK). In addition, we further assessed the effect of GA in an ovariectomized mouse model, which indicated that GA has a notable effect on preventing bone loss. In conclusion, GA exerts notable effects in inhibiting osteoclastogenesis and preventing ovariectomy-induced bone loss, suggesting that GA is a potential agent in osteoporosis treatment.

Polycyclic aromatic hydrocarbons in bone homeostasis

Prolonged exposure to polycyclic aromatic hydrocarbons (PAHs) may result in autoimmune diseases, such as rheumatoid arthritis (RA) and osteoporosis (OP), which are based on an imbalance in bone homeostasis. These diseases are characterized by bone erosion and even a disruption in homeostasis, including in osteoblasts and osteoclasts. Current evidence indicates that multiple factors affect the progression of bone homeostasis, such as genetic susceptibility and epigenetic modifications. However, environmental factors, especially PAHs from various sources, have been shown to play an increasingly prominent role in the progression of bone homeostasis. Hence, it is essential to investigate the effects and pathogenesis of PAHs in bone homeostasis. In this review, recent progress is summarized concerning the effects and mechanisms of PAHs and their ligands and receptors in bone homeostasis. Moreover, strategies based on the effects and mechanisms of PAHs in the regulation of the bone balance and alleviation of bone destruction are also reviewed. We further discuss the future challenges and perspectives regarding the roles of PAHs in autoimmune diseases based on bone homeostasis.