Modulation of osteoclast differentiation and function by the new members of the tumor necrosis factor receptor and ligand families

Repurposing the multiple sclerosis drug Siponimod for osteoporosis treatment

Osteoporosis is the most common bone disorder, in which an imbalance between osteoclastic bone resorption and osteoblastic bone formation disrupts bone homeostasis. Osteoporosis management using anti-osteoclastic agents is a promising strategy; however, this remains an unmet need. Sphingosine-1-phosphate (S1P) and its receptors (S1PRs) are essential for maintaining bone homeostasis. Here, we identified that Siponimod, a Food and Drug Administration-approved S1PR antagonist for the treatment of multiple sclerosis, shows promising therapeutic effects against osteoporosis by inhibiting osteoclast formation and function. We found that Siponimod inhibited osteoclast formation in a dose-dependent manner without causing cytotoxicity. Podosome belt staining and bone resorption assays indicated that Siponimod treatment impaired osteoclast function. Western blot and qPCR assays demonstrated that Siponimod suppressed the expression of osteoclast-specific markers, including C-Fos, Nftac1, and Ctsk. Mechanistically, we validated that Siponimod downregulated receptor activator of nuclear factor kappa B ligand (RANKL)-induced Mitogen-activated protein kinases (MAPKs) and nuclear factor kappa B (NF-κB) signaling pathways during osteoclastogenesis. Moreover, in a preclinical mouse model, Siponimod prevented ovariectomy-induced bone loss by suppressing osteoclast activity in vivo. Collectively, these results suggest that Siponimod could serve as an alternative therapeutic agent for the treatment of osteoporosis.

Perinatal loss of galactosylceramidase in both oligodendrocytes and microglia is crucial for the pathogenesis of Krabbe disease in mice

Lysosomal galactosylceramidase (GALC) is expressed in all brain cells, including oligodendrocytes (OLs), microglia, and astrocytes, although the cell-specific function of GALC is largely unknown. Mutations in GALC cause Krabbe disease (KD), a fatal neurological lysosomal disorder that usually affects infants. To study how Galc ablation in each glial cell type contributes to Krabbe pathogenesis, we used conditional Galc-floxed mice. Here, we found that OL-specific Galc conditional knockout (CKO) in mice results in a phenotype that includes wasting, psychosine accumulation, and neuroinflammation. Microglia- or astrocyte-specific Galc deletion alone in mice did not show specific phenotypes. Interestingly, mice with CKO of Galc from both OLs and microglia have a more severe neuroinflammation with an increase in globoid cell accumulation than OL-specific CKO alone. Moreover, the enhanced phenotype occurred without additional accumulation of psychosine. Further studies revealed that Galc knockout (Galc-KO) microglia cocultured with Galc-KO OLs elicits globoid cell formation and the overexpression of osteopontin and monocyte chemoattractant protein-1, both proteins that are known to recruit immune cells and promote engulfment of debris and damaged cells. We conclude that OLs are the primary cells that initiate KD with an elevated psychosine level and microglia are required for the progression of neuroinflammation in a psychosine-independent manner.

Effects of mineral trioxide aggregate and methyl sulfonyl methane on pulp exposure via RUNX2 and RANKL pathways

The aim of this study was to determine the therapeutic effects of mineral trioxide aggregate (MTA) and methyl sulfonyl methane (MSM) on pulp damage due to pulp exposure through the RUNX2 and RANKL pathways. Seventy-two male Sprague-Dawley rats aged 4-6 months and weighing 250-300 g were divided into healthy, control, MTA, and MSM groups. After experimental applications, all rats at 2, 4, and 8 weeks were killed anesthetically with xylazine hydrochloride (Rompun, Bayer) 30 mg/kg and ketamine hydrochloride (Ketalar, Pfizer) 50 mg/kg injections (i.p.). We observed that necrotic odontoblasts, edema, inflammation, and vascular congestion findings were reduced from week 2 to week 8 in the MSM treatment group after pulp capping compared to the control group and MTA group. Similarly, we found a decrease in RUNX2 and RANKL levels in the MSM application group compared to the control and MTA groups (p < 0.05). MSM material has shown therapeutic effects on pulp capping treatment-induced pulp injury via increased RUNX2 ve RANKL expression.

Drug-induced osteoporosis and mechanisms of bone tissue regeneration through trace elements

Osteoporosis is associated with an imbalance in bone formation, with certain drugs used in disease treatment being implicated in its development. Supplementation with trace elements may contribute to bone regeneration, offering an alternative approach by enhancing bone mineral density (BMD) and thereby thwarting the onset of osteoporosis. This review aims to assess the mechanisms through which trace elements such as copper (Cu), iron (Fe), selenium (Se), manganese (Mn), and zinc (Zn) are linked to increased bone mass, thus mitigating the effects of pharmaceuticals. Our findings underscore that the use of drugs such as aromatase inhibitors (AIs), proton pump inhibitors (PPIs), antiretrovirals, glucocorticoids, opioids, or anticonvulsants can result in decreased BMD, a primary contributor to osteoporosis. Research indicates that essential elements like Cu, Fe, Se, Mn, and Zn, through various mechanisms, can bolster BMD and forestall the onset of the disease, owing to their protective effects. Consequently, our study recommends a minimum daily intake of these essential minerals for patients undergoing treatment with the aforementioned drugs, as the diverse mechanisms governing the effects of trace elements Cu, Fe, Mn, Se, and Zn facilitate bone remodeling.

Characterization of a spontaneous osteopetrosis model using RANKL-dysfunctional mice

Tumor necrosis factor superfamily member 11 (TNFSF11), or receptor activator of nuclear factor-κB ligand (RANKL), is a crucial osteoclast-stimulating factor binding to RANK on osteoclast membranes. Mouse models are powerful tools for understanding the genetic mechanisms of related diseases. Here, we examined the utility of Tnfsf11 mutation in mice for understanding the mechanisms of bone remodeling and dysmorphology. The Tnfsf11gum mouse, discovered in 2011 at Jackson Laboratory, was used to study the genetic landscape associated with TNFSF11 inactivation in bone marrow tissues. Tnfsf11gum/+ and Tnfsf11+/+ mice were subjected to Micro-CT observation, ELISA analysis, histological evaluation, and massively-parallel mRNA sequencing (RNA-Seq) analysis. Tnfsf11gum/+ mice exhibited severe osteopetrotic changes in the bone marrow cavity, along with significantly lower serum RANKL levels and a reduced number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts in the bone marrow compared to those in Tnfsf11+/+ mice. However, tooth eruption between Tnfsf11gum/+ and Tnfsf11+/+ mice did not differ. Furthermore, genes involved in osteoblast proliferation and differentiation, including Gli1, Slc35b2, Lrrc17, and Junb were differentially expressed. Heterozygous mutation of TNFSF11 was also associated with a slightly increased expression of genes involved in osteoclast proliferation and differentiation, including Tcirg1, Junb, Anxa2, and Atp6ap1. Overall, we demonstrate that single gene mutations in Tnfsf11 cause bone resorption instability without significantly altering the genes related to osteoblast and osteoclast activity in the bone marrow cavity, thus establishing an optimal resource as an experimental animal model for bone resorption in bone biology research.

Trimethylamine-N-oxide promotes osteoclast differentiation and oxidative stress by activating NF-κB pathway

BACKGROUND

Senile osteoporosis may be caused by an imbalance in intestinal flora and oxidative stress. Trimethylamine-N-oxide (TMAO), a metabolite of dietary choline dependent on gut microbes, has been found to be significantly increased in osteoporosis. However, the role of TMAO in bone loss during osteoporosis remains poorly understood. In this study, we examined the impact of TMAO on osteoclast differentiation and bone resorption in an in vitro setting.

METHODS

Osteoclast differentiation was induced by incubating RAW 264.7 cells in the presence of Receptor Activator for Nuclear Factor-κB Ligand (RANKL) and macrophage-stimulating factor (M-CSF). Flow cytometry, TRAP staining assay, CCK-8, and ELISA were employed to investigate the impact of TMAO on osteoclast differentiation and bone resorption activity in vitro. For mechanistic exploration, RT-PCR and Western blotting were utilized to assess the activation of the NF-κB pathway. Additionally, protein levels of secreted cytokines and growth factors were determined using suspension array technology.

RESULTS

Our findings demonstrate that TMAO enhances RANKL and M-CSF-induced osteoclast formation and bone resorption in a dose-dependent manner. Mechanistically, TMAO triggers the upregulation of the NF-κB pathway and osteoclast-related genes (NFATc1, c-Fos, NF-κB p65, Traf6, and Cathepsin K). Furthermore, TMAO markedly elevated the levels of oxidative stress and inflammatory factors.

CONCLUSIONS

In conclusion, TMAO enhances RANKL and M-CSF-induced osteoclast differentiation and inflammation in RAW 264.7 cells by activating the NF-κB signaling pathway. These findings offer a new rationale for further academic and clinical research on osteoporosis treatment.

[miRNA Is Involved in the Pathogenesis of Multiple Diseases by Targeting Osteoprotegerin]

As a member of the tumor necrosis factor receptor family, osteoprotegerin (OPG) is highly expressed in adults in the lung, heart, kidney, liver, spleen, thymus, prostate, ovary, small intestines, thyroid gland, lymph nodes, trachea, adrenal gland, the testis, and bone marrow. Together with the receptor activator of nuclear factor-κB (RANK) and the receptor activator of nuclear factor-κB ligand (RANKL), it forms the RANK/RANKL/OPG pathway, which plays an important role in the molecular mechanism of the development of various diseases. MicroRNAs (miRNAs) are a class of endogenous non-coding RNAs performing regulatory functions in eukaryotes, with a size of about 20-25 nucleotides. miRNA genes are transcribed into primary transcripts by RNA polymerase, bind to RNA-induced silencing complexes, identify target mRNAs through complementary base pairing, with a single miRNA being capable of targeting hundreds of mRNAs, and influence the expression of many genes through pathways involved in functional interactions. In recent years, a large number of studies have been done to explore the mechanism of action of miRNA in diseases through miRNA isolation, miRNA quantification, miRNA spectrum analysis, miRNA target detection, in vitro and in vivo regulation of miRNA levels, and other technologies. It was found that miRNA can play a key role in the pathogenesis of osteoporosis, rheumatoid arthritis, and other diseases by targeting OPG. The purpose of this review is to explore the interaction between miRNA and OPG in various diseases, and to propose new ideas for studying the mechanism of action of OPG in diseases.

The Effect of Denosumab on Rotator Cuff Repair in Women Aged 60 and over with Osteoporosis: A Prospective Observational Study

BACKGROUND

In previous studies, denosumab, a RANKL human monoclonal antibody used in osteoporosis treatment, has shown efficacy in tendon healing after rotator cuff repair. This prospective study investigated the effects of denosumab on tendon healing, re-tear rates, and clinical outcomes post rotator cuff repair in women with osteoporosis.

METHOD

This was a prospective, observational study, employing propensity score matching for the control group. From March 2018 to March 2023, female patients over the age of 60 with normal bone density undergoing arthroscopic rotator cuff repair were selected as controls through propensity score matching (PSM) and compared with female patients of the same age group with osteoporosis who were receiving denosumab treatment. The control group was matched using 1-to-2 propensity score matching. Radiological examinations and functional outcomes were assessed preoperatively and at 6 months postoperatively.

RESULTS

In the final analysis, the study comprised 34 patients in the denosumab treatment group (Group 1) and 68 patients in the control group (Group 2). The functional scores showed significant improvement at 6 months post-surgery in both groups. No significant difference in the functional scores was observed among the groups. The re-tear rate, defined according to Sugaya's classification (types IV and V) as re-tear, was slightly higher in Group 1 at 16.7% (6 of 34) compared to Group 2 at 11.7% (8 of 68), but the difference was not statistically significant (p = 0.469). The re-tear patterns, classified according to Rhee's classification, also showed no significant difference among the groups (Group 1: 2/4 of 6; Group 2: 4/4 of 8; p = 0.571). The occurrence of type I re-tear exhibited no significant difference between the two groups (5.9% vs. 5.9%; p = 1.000).

CONCLUSIONS

The administration of denosumab following arthroscopic rotator cuff repair in women aged 60 and over with osteoporosis resulted in a re-tear rate that was similar to that observed in patients without osteoporosis. This result suggests that denosumab administration might be beneficial for rotator cuff healing, particularly in the context of osteoporosis, a known risk factor for increased retear rates. Therefore, comprehensive osteoporosis screening and treatment should be considered in conjunction with rotator cuff repair surgery in middle-aged women.

Bone and Extracellular Signal-Related Kinase 5 (ERK5)

Bones are vital for anchoring muscles, tendons, and ligaments, serving as a fundamental element of the human skeletal structure. However, our understanding of bone development mechanisms and the maintenance of bone homeostasis is still limited. Extracellular signal-related kinase 5 (ERK5), a recently identified member of the mitogen-activated protein kinase (MAPK) family, plays a critical role in the pathogenesis and progression of various diseases, especially neoplasms. Recent studies have highlighted ERK5's significant role in both bone development and bone-associated pathologies. This review offers a detailed examination of the latest research on ERK5 in different tissues and diseases, with a particular focus on its implications for bone health. It also examines therapeutic strategies and future research avenues targeting ERK5.

Subchondral osteoclasts and osteoarthritis: new insights and potential therapeutic avenues

Osteoarthritis (OA) is the most common joint disease, and good therapeutic results are often difficult to obtain due to its complex pathogenesis and diverse causative factors. After decades of research and exploration of OA, it has been progressively found that subchondral bone is essential for its pathogenesis, and pathological changes in subchondral bone can be observed even before cartilage lesions develop. Osteoclasts, the main cells regulating bone resorption, play a crucial role in the pathogenesis of subchondral bone. Subchondral osteoclasts regulate the homeostasis of subchondral bone through the secretion of degradative enzymes, immunomodulation, and cell signaling pathways. In OA, osteoclasts are overactivated by autophagy, ncRNAs, and Rankl/Rank/OPG signaling pathways. Excessive bone resorption disrupts the balance of bone remodeling, leading to increased subchondral bone loss, decreased bone mineral density and consequent structural damage to articular cartilage and joint pain. With increased understanding of bone biology and targeted therapies, researchers have found that the activity and function of subchondral osteoclasts are affected by multiple pathways. In this review, we summarize the roles and mechanisms of subchondral osteoclasts in OA, enumerate the latest advances in subchondral osteoclast-targeted therapy for OA, and look forward to the future trends of subchondral osteoclast-targeted therapies in clinical applications to fill the gaps in the current knowledge of OA treatment and to develop new therapeutic strategies.

Phillygenin prevents osteoclast differentiation and bone loss by targeting RhoA

Forsythia suspensa tea is a popular traditional Chinese medicine decoction for its healthy and therapeutic benefits. However, its effects in bone metabolism were not clear. In recent study, we uncovered anti-osteoclastogenesis property of Phillygenin (Phi), a compound abundant in Forsythia suspensa leaves, and aimed to investigate the effect and mechanism of Phi on bone metabolism in vivo and in vitro. Lipopolysaccharides-induced murine calvaria osteolysis and ovariectomy-induced bone loss animal models were used to identify the bone-protective effect of Phi in vivo and micro-CT, pQCT, and TRAP staining were applied. We used CCK8, TUNEL, BrdU, and TRAP staining to evaluate the efficacy of Phi on the proliferation and formation of OCs in primary mBMMs. RNA sequence, activity-based protein profiling, molecular docking, G-LISA, and WB were used to inspect the target and underlying mechanism of Phi's actions in mBMMs. We found Phi significantly inhibited bone resorption in vivo and inhibited mBMMs osteoclastogenesis in vitro. Ras homolog gene family member A (RhoA) was identified as the direct target of Phi. It counteracted the effects of RhoA activator and acted as a RhoA inhibitor. By targeting RhoA, Phi modulated Rho-associated coiled-coil containing protein kinase 1 (ROCK1) activity and regulated its downstream NF-κB/NFATc1/c-fos pathway. Furthermore, Phi depressed the disassembling of F-actin ring through cofilin and myosin1a. Our findings provided Phi as a potential option for treating bone loss diseases by targeting RhoA and highlighted the importance of F. suspensa as a preventive approach in bone disorders.

Multiple effects of dose-related GM-CSF on periodontal resorption in deep-frozen grafted teeth: A reverse study

Autologous tooth grafting is a dental restorative modality based on periodontal ligament healing.Human periodontal ligament stem cells(PDLSCs) are involved in the formation and remodeling of periodontal tissue.Based on previous findings, the proliferation and differentiation of processing cryopreserved periodontal ligament stem cells (PDLSCs) exhibit similarities to those of fresh cells. However, there is evident absorption in the transplanted frozen tooth's roots and bones, with the underlying cause remaining unknown. Granulocyte macrophage colony-stimulating factor(GM-CSF) is named for its produce granulocyte and macrophage precursors from bone marrow precursors, and it also serves as one of the regulatory factors in inflammatory and osteoclast formation. This study aimed to investigate changes in GM-CSF expression in frozen PDLSCs (fhPDLSCs) and evaluate the impact of GM-CSF on PDLSCs with respect to cellular activity and osteogenic ability. The role of GM-CSF in periodontal absorption was further speculated by comparing with IL-1β. The results revealed a significant increase in GM-CSF levels from fhPDLSCs compared to fresh cells, which exhibited an equivalent inflammatory stimulation effect as 1 ng/ml IL-1β. Cell viability also increased with increasing concentrations of GM-CSF; however, the GM-CSF from fhPDLSCs was not sufficient to significantly trigger osteoclastic factors. Considering its interaction with IL-1β and positive feedback mechanism, environments with high doses of GM-CSF derived from fhPDLSCs are more likely to activate osteoclastic responses.Therefore, for frozen tooth replantation, great attention should be paid to anti-inflammation and anti-infection.GM-CSF may serve as a potential therapeutic target for inhibiting periodontal resorption in delayed grafts.

Does Microwave Exposure at Different Doses in the Pre/Postnatal Period Affect Growing Rat Bone Development?

Effects of pre/postnatal 2.45 GHz continuous wave (CW), Wireless-Fidelity (Wi-Fi) Microwave (MW) irradiation on bone have yet to be well defined. The present study used biochemical and histological methods to investigate effects on bone formation and resorption in the serum and the tibia bone tissues of growing rats exposed to MW irradiation during the pre/postnatal period. Six groups were created: one control group and five experimental groups subjected to low-level different electromagnetic fields (EMF) of growing male rats born from pregnant rats. During the experiment, the bodies of all five groups were exposed to 2.45 GHz CW-MW for one hour/day. EMF exposure started after fertilization in the experimental group. When the growing male rats were 45 days old in the postnatal period, the control and five experimental groups' growing male and maternal rats were sacrificed, and their tibia tissues were removed. Maternal rats were not included in the study. No differences were observed between the control and five experimental groups in Receptor Activator Nuclear factor-kB (RANK) biochemical results. In contrast, there was a statistically significant increase in soluble Receptor Activator of Nuclear factor-kB Ligand (sRANKL) and Osteoprotegerin (OPG) for 10 V/m and 15 V/m EMF values. Histologically, changes in the same groups supported biochemical results. These results indicate that pre/postnatal exposure to 2.45 GHz EMF at 10 and 15 V/m potentially affects bone development.

Bone Formation and Maintenance in Oral Surgery: The Decisive Role of the Immune System-A Narrative Review of Mechanisms and Solutions

Based on the evidence of a significant communication and connection pathway between the bone and immune systems, a new science has emerged: osteoimmunology. Indeed, the immune system has a considerable impact on bone health and diseases, as well as on bone formation during grafts and its stability over time. Chronic inflammation induces the excessive production of oxidants. An imbalance between the levels of oxidants and antioxidants is called oxidative stress. This physio-pathological state causes both molecular and cellular damage, which leads to DNA alterations, genetic mutations and cell apoptosis, and thus, impaired immunity followed by delayed or compromised wound healing. Oxidative stress levels experienced by the body affect bone regeneration and maintenance around teeth and dental implants. As the immune system and bone remodeling are interconnected, bone loss is a consequence of immune dysregulation. Therefore, oral tissue deficiencies such as periodontitis and peri-implantitis should be regarded as immune diseases. Bone management strategies should include both biological and surgical solutions. These protocols tend to improve immunity through antioxidant production to enhance bone formation and prevent bone loss. This narrative review aims to highlight the relationship between inflammation, oxidation, immunity and bone health in the oral cavity. It intends to help clinicians to detect high-risk situations in oral surgery and to propose biological and clinical solutions that will enhance patients' immune responses and surgical treatment outcomes.

Expression and functional characterization of bovine receptor activator of NF-κB ligand (RANKL)

Receptor activator of nuclear factor Kappa-B Ligand (RANKL) is a member of the tumor necrosis factor ligand (TNF) family involved in immune responses and immunomodulation. Expressed in various cells types around the body, RANKL plays a crucial role in bone remodeling and development of the thymus, lymph nodes and mammary glands. Research in other species demonstrates that RANKL is required for the development of microfold cells (M cells) in the gut, however limited information specific to cattle is available. Cloning and expression of bovine RANKL (BoRANKL) was carried out and bioactivity of the protein was demonstrated in the induction of osteoclast differentiation from both bovine and ovine bone marrow cells. The effects of BoRANKL on particle uptake in bovine enteroids was also assessed. The production of cross-reactive bovine RANKL protein will enable further investigations into cell differentiation using the available ruminant organoid systems, and their role in investigating host-pathogen interactions in cattle and sheep.

Stem cells derived from human exfoliated deciduous teeth-based media in a rat root resorption model

OBJECTIVE

Root resorption may occur during orthodontic treatment. Herein, we investigated the effect of a culture supernatant of stem cells derived from human exfoliated deciduous teeth on root resorption.

DESIGN

Twelve 8-week-old male Sprague-Dawley rats were used, and their maxillary first molars were pulled with excessive orthodontic force to induce root resorption. On days 1 and 7 after traction initiation, stem cells derived from human exfoliated deciduous teeth and alpha minimum essential medium (control group) were administered. After 14 days, the maxillary bone was evaluated for tooth movement. The expression of osteoprotegerin, receptor activator of nuclear factor κB ligand, tumor necrosis factor α, interleukin 1β, interleukin 6, and interleukin 17 was evaluated on the compression side and tension side.

RESULTS

No significant difference in tooth movement was observed between the two groups. Root resorption decreased in the group administered the culture supernatant compared with in the control. Immunohistochemical staining revealed increased osteoprotegerin expression and decreased receptor activators for nuclear factor κB ligand, tumor necrosis factor α, interleukin 1β, interleukin 6, and interleukin 17 on the compression side and tension side.

CONCLUSIONS

Administration of stem cells derived from human exfoliated deciduous teeth affected the expression of osteoprotegerin, receptor activator of nuclear factor κB ligand, tumor necrosis factor α, interleukin 1β, interleukin 6 and interleukin 17; hence, these stem cells may inhibit root resorption by regulating their expression.

Roles of IL-11 in the regulation of bone metabolism

Bone metabolism is the basis for maintaining the normal physiological state of bone, and imbalance of bone metabolism can lead to a series of metabolic bone diseases. As a member of the IL-6 family, IL-11 acts primarily through the classical signaling pathway IL-11/Receptors, IL-11 (IL-11R)/Glycoprotein 130 (gp130). The regulatory role of IL-11 in bone metabolism has been found earlier, but mainly focuses on the effects on osteogenesis and osteoclasis. In recent years, more studies have focused on IL-11's roles and related mechanisms in different bone metabolism activities. IL-11 regulates osteoblasts, osteoclasts, BM stromal cells, adipose tissue-derived mesenchymal stem cells, and chondrocytes. It's involved in bone homeostasis, including osteogenesis, osteolysis, bone marrow (BM) hematopoiesis, BM adipogenesis, and bone metastasis. This review exams IL-11's role in pathology and bone tissue, the cytokines and pathways that regulate IL-11 expression, and the feedback regulations of these pathways.

Non-biofilm-forming Staphylococcus epidermidis planktonic cell supernatant induces alterations in osteoblast biological function

Staphylococcal biofilms significantly contribute to prosthetic joint infection (PJI). However, 40% of S. epidermidis PJI isolates do not produce biofilms, which does not explain the role of biofilms in these cases. We studied whether the supernatant from planktonic S. epidermidis alters osteoblast function. Non-biofilm-forming S. epidermidis supernatants (PJI- clinical isolate, healthy skin isolate (HS), and ATCC12228 reference strain) and biofilm-forming supernatants (PJI+ clinical isolate, ATCC35984 reference strain, and Staphylococcus aureus USA300 reference strain) were included. Osteoblasts stimulated with supernatants from non-biofilm-forming isolates for 3, 7, and 14 days showed significantly reduced cellular DNA content compared with unstimulated osteoblasts, and apoptosis was induced in these osteoblasts. Similar results were obtained for biofilm-forming isolates, but with a greater reduction in DNA content and higher apoptosis. Alkaline phosphatase activity and mineralization were significantly reduced in osteoblasts treated with supernatants from non-biofilm-forming isolates compared to the control at the same time points. However, the supernatants from biofilm-forming isolates had a greater effect than those from non-biofilm-forming isolates. A significant decrease in the expression of ATF4, RUNX2, ALP, SPARC, and BGLAP, and a significant increase in RANK-L expression were observed in osteoblasts treated with both supernatants. These results demonstrate that the supernatants of the S. epidermidis isolate from the PJI- and HS (commensal) with a non-biofilm-forming phenotype alter the function of osteoblasts (apoptosis induction, failure of cell differentiation, activation of osteoblasts, and induction of bone resorption), similar to biofilm-forming isolates (PJI+, ATCC35984, and S. aureus USA300), suggesting that biofilm status contributes to impaired osteoblast function and that the planktonic state can do so independently of biofilm production.

Hypertension and Dental Implants: A Systematic Review and Meta-Analysis

PURPOSE

The aim of the present systematic review was to investigate the influence of hypertension on the dental implant failure rate.

METHODS

An electronic search was undertaken in four databases, plus a manual search of journals. The I2 statistic was used to check heterogeneity and the inverse-variance method was used for the meta-analysis. The estimate of relative effect for dichotomous outcome was expressed as an odds ratio (OR).

RESULTS

The review included 24 publications. There were 4874 implants (257 failures) placed in hypertensive patients and 16,192 implants (809 failures) placed in normotensive patients. A pairwise meta-analysis showed that implants in hypertensive patients did not have a higher risk of failure than implants placed in normotensive patients (OR 1.100, p = 0.671). The log OR of implant failure between hypertensive and normotensive patients did not significantly change with the follow-up time (p = 0.824).

CONCLUSIONS

This review suggests that implants in hypertensive patients do not present higher odds of failure in comparison to normotensive patients. However, further research on this topic, with the use of more rigorous criteria to diagnose patients as being hypertensive, as well as clearer information about the pharmacological management of the condition in the patients, is recommended.

Aging effects on osteoclast progenitor dynamics affect variability in bone turnover via feedback regulation

Bone turnover markers (BTMs) are commonly used in osteoporosis treatment as indicators of cell activities of bone-resorbing osteoclasts and bone-forming osteoblasts. The wide variability in their values due to multiple factors, such as aging and diseases, makes it difficult for physicians to utilize them for clinical decision-making. The progenitors of osteoclasts and osteoblasts are indispensable for a comprehensive interpretation of the variability in BTM values because these upstream progenitors strongly regulate the downstream cell activities of bone turnover. However, understanding the complex interactions among the multiple populations of bone cells is challenging. In this study, we aimed to gain a fundamental understanding of the mechanism by which the progenitor dynamics affect the variability in bone turnover through in silico experiments by exploring the cell dynamics with aging effects on osteoporosis. Negative feedback control driven by the consumptive loss of progenitors prevents rapid bone loss due to excessive bone turnover, and through feedback regulation, aging effects on osteoclast differentiation and osteoclast progenitor proliferation cause variability in the osteoclast and osteoblast activity balance and its temporal transition. By expressing the variability in the bone turnover status, our model describes the individualities of patients based on their clinical backgrounds. Therefore, our model could play a powerful role in assisting tailored treatment and has the potential to resolve the various health problems associated with osteoporosis worldwide.

Integration of osteoclastogenesis through addition of PBMCs in human osteochondral explants cultured ex vivo

The preservation of tissue specific cells in their native 3D extracellular matrix in bone explants provides a unique platform to study remodeling. Thus far, studies involving bone explant cultures showed a clear focus on achieving bone formation and neglected osteoclast activity and resorption. To simulate the homeostatic bone environment ex vivo, both key elements of bone remodeling need to be represented. This study aimed to assess and include osteoclastogenesis in human osteochondral explants through medium supplementation with RANKL and M-CSF and addition of peripheral blood mononuclear cells (PBMCs), providing osteoclast precursors. Osteochondral explants were freshly harvested from human femoral heads obtained from hip surgeries and cultured for 20 days in a two-compartment culture system. Osteochondral explants preserved viability and cellular abundance over the culture period, but histology demonstrated that resident osteoclasts were no longer present after 4 days of culture. Quantitative extracellular tartrate resistant acid phosphatase (TRAP) analysis confirmed depletion of osteoclast activity on day 4 even when stimulated with RANKL and M-CSF. Upon addition of PBMCs, a significant upregulation of TRAP activity was measured from day 10 onwards. Evaluation of bone loss trough μCT registration and measurement of extracellular cathepsin K activity revealed indications of enhanced resorption upon addition of PBMCs. Based on the results we suggest that an external source of osteoclast precursors, such as PBMCs, needs to be added in long-term bone explant cultures to maintain osteoclastic activity, and bone remodeling.

Multifunctional gold nanoparticles for osteoporosis: synthesis, mechanism and therapeutic applications

Osteoporosis is currently the most prevalent bone disorder worldwide and is characterized by low bone mineral density and an overall increased risk of fractures. To treat osteoporosis, a range of drugs targeting bone homeostasis have emerged in clinical practice, including anti-osteoclast agents such as bisphosphonates and denosumab, bone formation stimulating agents such as teriparatide, and selective oestrogen receptor modulators. However, traditional clinical medicine still faces challenges related to side effects and high costs of these types of treatments. Nanomaterials (particularly gold nanoparticles [AuNPs]), which have unique optical properties and excellent biocompatibility, have gained attention in the field of osteoporosis research. AuNPs have been found to promote osteoblast differentiation, inhibit osteoclast formation, and block the differentiation of adipose-derived stem cells, which thus is believed to be a novel and promising candidate for osteoporosis treatment. This review summarizes the advances and drawbacks of AuNPs in their synthesis and the mechanisms in bone formation and resorption in vitro and in vivo, with a focus on their size, shape, and chemical composition as relevant parameters for the treatment of osteoporosis. Additionally, several important and promising directions for future studies are also discussed, which is of great significance for prevention and treatment of osteoporosis.

USP7 Inhibits Osteoclastogenesis via Dual Effects of Attenuating TRAF6/TAK1 Axis and Stimulating STING Signaling

Ubiquitination is a reversible post-translational modification implicated in cell differentiation, homeostasis, and organ development. Several deubiquitinases (DUBs) decrease protein ubiquitination through the hydrolysis of ubiquitin linkages. However, the role of DUBs in bone resorption and formation is still unclear. In this study, we identified DUB ubiquitin-specific protease 7 (USP7) as a negative regulator of osteoclast formation. USP7 combines with tumor necrosis factor receptor-associated factor 6 (TRAF6) and inhibits its ubiquitination by impairing the Lys63-linked polyubiquitin chain. Such impairment leads to the suppression of receptor activator of NF-κB ligand (RANKL)-mediated nuclear factor-κB (NF-κB) and mitogen-activated protein kinases (MAPKs) activation without affecting TRAF6 stability. USP7 also protects the stimulator of interferon genes (STING) against degradation, inducing interferon-β (IFN-β) expression in osteoclast formation, thereby inhibiting osteoclastogenesis cooperatively with the classical TRAF6 pathway. Furthermore, USP7 inhibition accelerates osteoclast differentiation and bone resorption both in vitro and in vivo. Contrarily, USP7 overexpression impairs osteoclast differentiation and bone resorption in vitro and in vivo. Additionally, in ovariectomy (OVX) mice, USP7 levels are lower than those in sham-operated mice, suggesting that USP7 plays a role in osteoporosis. Altogether, our data reveal the dual effect of USP7-mediated TRAF6 signal transduction and USP7-mediated protein degradation of STING in osteoclast formation.

The role of NFATc1 in the progression and metastasis of prostate cancer: A review on the molecular mechanisms and signaling pathways

A common type of cancer among men is the prostate cancer that kills many people every year. The multistage of this disease and the involvement of the vital organs of the body have reduced the life span and quality of life of the people involved and turned the treatment process into a complex one. NFATc1 biomarker contributes significantly in the diagnosis and treatment of this disease by increasing its expression in prostate cancer and helping the proliferation, differentiation, and invasion of cancer cells through different signaling pathways. NFATc1 is also able to target the metabolism of cancer cells by inserting specific oncogene molecules such as c-myc that it causes cell growth and proliferation. Bone is a common tissue where prostate cancer cells metastasize. In this regard, the activity of NFATc1, through the regulation of different signaling cascades, including the RANKL/RANK signaling pathway, in turn, increases the activity of osteoclasts, and as a result, bone tissue is gradually ruined. Using Silibinin as a medicinal plant extract can inhibit the activity of osteoclasts related to prostate cancer by targeting NFATc. Undoubtedly, NFATc1 is one of the effective oncogenes related to prostate cancer, which has the potential to put this cancer on the path of progression and metastasis. In this review, we will highlight the role of NFATc1 in the progression and metastasis of prostate cancer. Furthermore, we will summarize signaling pathways and molecular mechanism, through which NFATc1 regulates the process of prostate cancer.

Bone Remodeling and Modeling: Cellular Targets for Antiresorptive and Anabolic Treatments, Including Approaches Through the Parathyroid Hormone (PTH)/PTH-Related Protein Pathway

Bone is continuously in a state of building and renewal, though the process of remodeling that takes place at many sites asynchronously throughout the skeleton, with bone formation and resorption equal at these sites (bone multicellular units). Remodeling takes place on bone surfaces, both on trabeculae and in the cortex, and serves the purposes of replacing old bone or that damaged by microfractures throughout the skeleton. The bone loss and consequent osteoporotic fractures that result from excess resorption over formation have mainly been prevented or treated by antiresorptive drugs that inhibit osteoclast formation and/or activity. Virtually all of the evidence leading to acceptance of antiresorptive drugs as treatment has depended upon their prevention of vertebral fractures. In recent decades, new prospects came of anabolic treatments that partly restore bone volume and microstructure restore bone that has been lost. The first of these was parathyroid hormone (PTH), shown by daily injection to increase markers of bone formation and prevent fractures. This field of interest enlarged with the discovery of PTH-related protein (PTHrP), so closely related in structure and action to PTH. The structural relationship between PTH and PTHrP is important in assessing their physiological and pharmacological roles, with the N-terminal domains of the 2 having virtually equal actions on target cells. Abaloparatide, a peptide analogue based on the structures of PTHrP and PTH, has been approved in some countries as a therapy for osteoporosis. Treatment through the PTH receptor activation pathway, and probably with any anabolic therapy, needs to be followed by antiresorptive treatment in order to maintain bone that has been restored. No matter how effective anabolic therapies for the skeleton become, it seems highly likely that there will be a continuing need for antiresorptive drugs.

Generating Bone Marrow Chimeric Mouse Using GPR120 Deficient Mouse for the Study of DHA Inhibitory Effect on Osteoclast Formation and Bone Resorption

Docosahexaenoic acid (DHA) is an omega-3 fatty acid that exerts physiological effects via G protein-coupled receptor 120 (GPR120). In our previous studies, we figured out the inhibitory effects of DHA on TNF-α (Tumor necrosis factor-α)-induced osteoclastogenesis via GPR120 in vivo. Moreover, DHA directly suppressed RANKL expression in osteoblasts via GPR120 in vitro. In this study, we generated bone marrow chimeric mice using GPR120 deficient mice (GPR120-KO) to study the inhibitory effects of DHA on bone resorption and osteoclast formation. Bone marrow cells of wild-type (WT) or GPR120-KO mice were transplanted into irradiated recipient mice, which were WT or GPR120 deficient mice. The resulting chimeric mice contained stromal cells from the recipient and bone marrow cells, including osteoclast precursors, from the donor. These chimeric mice were used to perform a series of histological and microfocus computed tomography (micro-CT) analyses after TNF-α injection for induction of osteoclast formation with or without DHA. Osteoclast number and bone resorption were found to be significantly increased in chimeric mice, which did not express GPR120 in stromal cells, compared to chimeric mice, which expressed GPR120 in stromal cells. DHA was also found to suppress specific signaling pathways. We summarized that DHA suppressed TNF-α-induced stromal-dependent osteoclast formation and bone resorption via GPR120.

Mechanisms of Osteoclastogenesis in Orthodontic Tooth Movement and Orthodontically Induced Tooth Root Resorption

Orthodontic tooth movement (OTM) is achieved by the simultaneous activation of bone resorption by osteoclasts and bone formation by osteoblasts. When orthodontic forces are applied, osteoclast-mediated bone resorption occurs in the alveolar bone on the compression side, creating space for tooth movement. Therefore, controlling osteoclastogenesis is the fundamental tenet of orthodontic treatment. Orthodontic forces are sensed by osteoblast lineage cells such as periodontal ligament (PDL) cells and osteocytes. Of several cytokines produced by these cells, the most important cytokine promoting osteoclastogenesis is the receptor activator of nuclear factor-κB ligand (RANKL), which is mainly supplied by osteoblasts. Additionally, osteocytes embedded within the bone matrix, T lymphocytes in inflammatory conditions, and PDL cells produce RANKL. Besides RANKL, inflammatory cytokines, such as interleukin-1, tumor necrosis factor-α, and prostaglandin E2 promote osteoclastogenesis under OTM. On the downside, excessive osteoclastogenesis activation triggers orthodontically-induced external root resorption (ERR) through pro-osteoclastic inflammatory cytokines. Therefore, understanding the mechanisms of osteoclastogenesis during OTM is essential in reducing the adverse effects of orthodontic treatment. Here, we review the current concepts of the mechanisms underlying osteoclastogenesis in OTM and orthodontically induced ERR.

Influence of type 2 diabetes on immunohistochemical detection of TRAF6, cFos and NFATC1 in the gingiva in cases of chronic periodontitis

Type 2 diabetes (T2D) and chronic periodontitis (CP) are common diseases worldwide. Although T2D increases the severity of CP and alveolar bone loss, the mechanism of this is not well understood. We investigated using immunohistochemistry the expression of three osteoclast proteins, TRAF6, cFos and NFATc1, in gingival tissues. Gingival tissues were obtained from three groups: HC group, healthy controls; CP group, patients with CP; T2D + CP group, patients with both T2D and CP. Strong immunostaining for TRAF6, cFos and NFATc1 was observed in the gingival epithelium as well as in inflammatory cells in the CP and T2D + CP groups. Immunostaining was most intense in the T2D + CP group. We found strong up-regulation of TRAF6, cFos and NFATC1 in gingiva tissue of subjects with both T2D and CP, which corroborates our hypothesis that T2D potentiates osteoclastogenesis in CP.

In Vitro Effect of Photobiomodulation Therapy with 980 nm Diode Laser on Gene Expression of Key Regulators of Bone Remodeling by Human Periodontal Ligament Cells under Mild Orthodontic Forces

This study investigated the effect of photobiomodulation (PBM) with 980 nm diode laser as monotherapy and in combination with compressive and tensile orthodontic forces on expression of osteoprotegerin (OPG), receptor activator of nuclear factor-κB ligand (RANKL), sclerostin (SOST) and periostin (POSTN), by human periodontal ligament cells. Isolated cells were cultured and subjected to either tensile (10% elongation) or compressive forces (25 g cm-2 ) for 24 and 48 h. Subsequently, the cells received PBM (100 mW power, 3 or 6 J cm-2 energy density) immediately after load cycle. RT-PCR was applied to assess the genes expression. Data were analyzed by one-way ANOVA, followed by post hoc Tukey test (P ≤ 0.05). We found that PBM in combination with orthodontic forces led to upregulation of bone resorption genes (RANKL and SOST) at the pressure side and their downregulation at the tension side. The expression of osteogenic genes (OPG and POSTN) increased at the tension side and decreased at the pressure side. PBM alone did not affect gene expression. In conclusion, these findings suggest that this PBM protocol may be effective in enhancement of the gene expression in favor of bone remodeling acceleration that should be confirmed in future animal and human studies.

Role of exosomes in prostate cancer bone metastasis

Bone is a preferred metastatic site of prostate cancer (PCa), and most patients with PCa metastases develop osteogenic bone metastasis, which manifests as disturbed bone structure and poor bone quality. However, the underlying mechanisms of PCa bone metastasis remain unclear. In recent years, increasing evidence has implicated extracellular vesicles, especially exosomes, in PCa bone metastasis. Exosomes are 30-150 nm in diameter, enclosing a cargo of biomolecules, such as DNA, RNA, and proteins. Exosomes play a functional role in intercellular communication, modulate the functions of recipient cells, and potentially modulate bone microenvironment changes, thereby influencing the development of PCa bone metastasis. This review summarizes the involvement of exosomes in the imbalance between bone resorption and formation, and establishing a pre-metastatic niche in bone marrow, as well as potential clinical applications of exosomes in therapeutic strategies for treating patients with advanced PCa with bone metastasis.

The Impact of Culture Variables on a 3D Human In Vitro Bone Remodeling Model: A Design of Experiments Approach

Human in vitro bone remodeling models, using osteoclast-osteoblast cocultures, can facilitate the investigation of human bone remodeling while reducing the need for animal experiments. Although current in vitro osteoclast-osteoblast cocultures have improved the understanding of bone remodeling, it is still unknown which culture conditions support both cell types. Therefore, in vitro bone remodeling models can benefit from a thorough evaluation of the impact of culture variables on bone turnover outcomes, with the aim to reach balanced osteoclast and osteoblast activity, mimicking healthy bone remodeling. Using a resolution III fractional factorial design, the main effects of commonly used culture variables on bone turnover markers in an in vitro human bone remodeling model are identified. This model is able to capture physiological quantitative resorption-formation coupling along all conditions. Culture conditions of two runs show promising results: conditions of one run can be used as a high bone turnover system and conditions of another run as a self-regulating system as the addition of osteoclastic and osteogenic differentiation factors is not required for remodeling. The results generated with this in vitro model allow for better translation between in vitro studies and in vivo studies, toward improved preclinical bone remodeling drug development.

The Role of XBP1 in bone metabolism

Bone is a dynamic organ that, once formed, undergoes a constant remodeling process that includes bone resorption and synthesis. Osteoclasts and osteoblasts are primarily responsible for controlling this process. X-box binding protein 1 (XBP1), a transcription factor, affects the metabolism of bones in various ways. In recent years, numerous studies have revealed that XBP1 plays a vital role in bone metabolism, including osteoclast and osteoblast development, as well as in regulating immune cell differentiation that affects the immune microenvironment of bone remodeling. In this review, we highlight the regulatory mechanisms of XBP1 on osteoclasts and osteoblasts, how XBP1 affects the immune microenvironment of bone remodeling by influencing the differentiation of immune cells, and predict the possible future research directions of XBP1 to provide new insights for the treatment of bone-related metabolic diseases.

Protective effects of curcumin against osteoporosis and its molecular mechanisms: a recent review in preclinical trials

Osteoporosis (OP) is one of the most common metabolic skeletal disorders and is commonly seen in the elderly population and postmenopausal women. It is mainly associated with progressive loss of bone mineral density, persistent deterioration of bone microarchitecture, and increased fracture risk. To date, drug therapy is the primary method used to prevent and treat osteoporosis. However, long-term drug therapy inevitably leads to drug resistance and specific side effects. Therefore, researchers are constantly searching for new monomer compounds from natural plants. As a candidate for the treatment of osteoporosis, curcumin (CUR) is a natural phenolic compound with various pharmacological and biological activities, including antioxidant, anti-apoptotic, and anti-inflammatory. This compound has gained research attention for maintaining bone health in various osteoporosis models. We reviewed preclinical and clinical studies of curcumin in preventing and alleviating osteoporosis. These results suggest that if subjected to rigorous pharmacological and clinical trials, naturally-derived curcumin could be used as a complementary and alternative medicine for the treatment of osteoporosis by targeting osteoporosis-related mechanistic pathways. This review summarizes the mechanisms of action and potential therapeutic applications of curcumin in the prevention and mitigation of osteoporosis and provides reference for further research and development of curcumin.

Phase I, Randomized, Placebo-Controlled, Dose-Escalation Study of GB223, a Fully-Humanized Monoclonal Antibody to RANKL, in Healthy Chinese Adults

BACKGROUND

GB223 is a novel, fully-humanized monoclonal antibody against the receptor activator of nuclear factor-kappa B ligand (RANKL). In this phase I study, the safety, tolerability, pharmacokinetics, pharmacodynamics, and immunogenicity of GB223 were investigated.

PATIENTS AND METHODS

This was a randomized, double-blinded, placebo-controlled, single-dose escalation study conducted in 44 healthy Chinese adults. Participants were randomly assigned to receive a single subcutaneous injection dose of 7, 21, 63, 119, or 140 mg of GB223 (n = 34) or placebo (n = 10) and were followed up for 140-252 days.

RESULTS

The results of noncompartmental analysis showed that GB223 was slowly absorbed after dosing, with a time to reach maximum concentration (Tmax) ranging from 5 to 11 days. Serum GB223 concentrations decreased slowly, with a long half-life ranging from 7.91 to 19.60 days. A two-compartment Michaelis-Menten model was found to best describe the pharmacokinetics of GB223, and the absorption rate of GB223 differed between males (0.0146 h-1) and females (0.0081 h-1). Serum C-terminal telopeptide of type I collagen decreased significantly postdose, and the inhibition lasted 42-168 days. No deaths or drug-related serious adverse events occurred. The most frequent adverse events were blood parathyroid hormone increased (94.1%), blood phosphorus decreased (67.6%) and blood calcium decreased (58.8%). In the GB223 group, 44.1% (15/34) of subjects were antidrug antibody positive after dosing.

CONCLUSION

In this study, we demonstrated for the first time that a single subcutaneous injection of GB223, from 7 to 140 mg, is safe and well tolerated in healthy Chinese subjects. GB223 has a nonlinear pharmacokinetic profile, and sex was a potential covariate that may affect the absorption rate of GB223.

CLINICAL TRIAL REGISTRATION

NCT04178044 and ChiCTR1800020338.

Musculoskeletal complications of Cushing syndrome

Prolonged exposure to an excess of glucocorticosteroids (GCs), both endogenous and exogenous, leads to a wide range of comorbidities, including cardiovascular, metabolic, psychiatric, and musculoskeletal disorders. The latter comprise osteopenia and osteoporosis leading to skeletal fractures and myopathy. Although endogenous hypercortisolemia is a rare disorder, GCs are among the most frequently prescribed drugs, often administered chronically and despite multiple side effects, impossible to taper off due to therapeutic reasons. The pathophysiology of the effect of GC excess on bone often leads to fractures despite normal or low-normal bone mineral density and it includes direct (mainly disturbance in bone formation processes, through inactivation of the Wnt/β-catenin signalling pathway) and indirect mechanisms (through suppressing the gonadal and somatotrophic axis, and also through antagonizing vitamin D actions). Glucocorticosteroid-induced fast-twitch, glycolytic muscles atrophy occurs due to increased protein catabolism and impaired synthesis. Protein degradation is a result of activation of the ubiquitin proteasome and the lysosomes stimulated through overexpression of several atrogenes (such as FOXO-1 and atrogin-1). This review will discuss pathophysiology, clinical presentation, prevention, and management of GC-induced osteoporosis (including calcium and vitamin D supplementation, and bisphosphonates) and myopathy associated with GC excess.

The Bone Microenvironment Soil in Prostate Cancer Metastasis: An miRNA Approach

Bone metastatic prostate cancer (PCa) is associated with a high risk of mortality. Changes in the expression pattern of miRNAs seem to be related to early aspects of prostate cancer, as well as its establishment and proliferation, including the necessary steps for metastasis. Here we compiled, for the first time, the important roles of miRNAs in the development, diagnosis, and treatment of bone metastasis, focusing on recent in vivo and in vitro studies. PCa exosomes are proven to promote metastasis-related events, such as osteoblast and osteoclast differentiation and proliferation. Aberrant miRNA expression in PCa may induce abnormal bone remodeling and support tumor development. Furthermore, miRNAs are capable of binding to multiple mRNA targets, a dynamic property that can be harnessed for the development of treatment tools, such as antagomiRs and miRNA mimics, which have emerged as promising candidates in PCa treatment. Finally, miRNAs may serve as noninvasive biomarkers, as they can be detected in tissue and bodily fluids, are highly stable, and show differential expression between nonmetastatic PCa and bone metastatic samples. Taken together, the findings underscore the importance of miRNA expression profiles and miRNA-based tools as rational technologies to increase the quality of life and longevity of patients.

Sclerostin: clinical insights in muscle-bone crosstalk

Sclerostin, a protein encoded by the sclerostin (SOST) gene, is mostly expressed in osteocytes. First described in the pathogenesis of three disorders, sclerosteosis, van Buchem's disease, and craniodiaphyseal dysplasia, sclerostin has been identified as an important regulator of bone homeostasis, controlling bone formation by osteoblasts through inhibition of the canonical Wnt signaling pathway. Recent studies have highlighted a hypothetical role of sclerostin in myogenesis, thus modulating the interaction between bone and muscle. This narrative review provides an overview of the clinical implications of sclerostin modulation on skeletal muscle mass and function, and bone metabolism. Improving knowledge about muscle-bone crosstalk may represent a turning point in the development of therapeutic strategies for musculoskeletal disorders, particularly osteosarcopenia.

Protaetia brevitarsis Extract Attenuates RANKL-Induced Osteoclastogenesis by Inhibiting the JNK/NF-κB/PLCγ2 Signaling Pathway

Protaetia brevitarsis (PB)-derived bioactive substances have been used as food and medicine in many Asian countries because of their antioxidant, antidiabetic, anti-cancer, and hepatoprotective properties. However, the effect of PB extracts (PBE) on osteoclast differentiation is unclear. In this study, we investigated the effect of PBE on RANKL-induced osteoclastogenesis in mouse bone marrow-derived macrophages (BMMs). To investigate the cytotoxicity of PBE, the viability of BMMs was confirmed via MTT assay. Tartrate-resistant acid phosphatase (TRAP) staining and pit assays were performed to confirm the inhibitory effect of PBE on osteoclast differentiation and bone resorption. The expression levels of osteoclast differentiation-related genes and proteins were evaluated using quantitative real-time PCR and Western blotting. PBE attenuated osteoclastogenesis in BMMs in TRAP and pit assays without cytotoxicity. The expression levels of osteoclast marker genes and proteins induced by RANKL were decreased after PBE treatment. PBE suppressed osteoclastogenesis by inhibiting the RANKL-induced activated JNK/NF-κB/PLCγ2 signaling pathway and the expression of NFATc1 and c-Fos. Collectively, these results suggest that PBE could be a potential therapeutic strategy or functional product for osteoclast-related bone disease.

Bone health in inflammatory bowel disease

INTRODUCTION

Inflammatory bowel disease (IBD) is a chronic disease characterized by the presence of systemic inflammation, manifesting not only as gastrointestinal symptoms but also as extraintestinal bone complications, including osteopenia and osteoporosis. However, the association between IBD and osteoporosis is complex, and the presence of multifactorial participants in the development of osteoporosis is increasingly recognized. Unlike in adults, delayed puberty and growth hormone/insulin-like growth factor-1 axis abnormalities are essential risk factors for osteoporosis in pediatric patients with IBD.

AREAS COVERED

This article reviews the potential pathophysiological mechanisms contributing to osteoporosis in adult and pediatric patients with IBD and provides evidence for effective prevention and treatment, focusing on pediatric patients with IBD. A search was performed from PubMed and Web of Science inception to February 2023 to identify articles on IBD, osteoporosis, pediatric, and fracture risk.

EXPERT OPINION

A comprehensive treatment pattern based on individualized principles can be used to manage pediatric IBD-related osteoporosis.

Inhibitory Effects of Wheat Sprouts Extract on RANKL-Induced Osteoclast Differentiation via Suppressing MAPK and NFATc1 Signaling Pathways

The maintenance of bone is dependent on both osteoclasts, which break down bone, and osteoblasts, which build new bone. Various bone-related disorders, including osteoporosis, can occur as a result of an imbalance between these two cell types. Prolonged use of currently available bone resorption inhibitors may show side effects. Therefore, developing a novel preventive material which effectively inhibits osteoclast differentiation could be beneficial. This study planned to investigate the inhibitory effect of wheat sprout ethanolic extracts (Saegeumgang [SGG] and Arriheuk [ARH]) on the differentiation of osteoclasts induced by RANKL, as well as the mechanisms why fundamental to these effects. The effects of SGG and ARH on bone resorption and osteoclast differentiation were evaluated using RAW 264.7 cells and assessed through TRAP cell count, pit formation, and activity. The expressions of mRNA and protein were accomplished using western blotting, and reverse transcription quantitative polymerase chain reaction analyses were conducted. SGG and ARH were found to suppress osteoclast differentiation in RANKL-stimulated RAW264.7 cells without causing cytotoxic effects. In addition, treatment with SGG and ARH led to a reduction in the number of cells with positive staining for TRAP and TRAP activity. SGG and ARH treatment dose-dependently decreased the pit area in pit formation assays, showing a notable reduction compared to the pit area created by mature osteoclasts. SGG and ARH inhibited osteoclast activity by 84.9% and 95.7% at 200 μg/mL, respectively. In addition, SGG and ARH suppressed the transcriptional activation of various osteoclast-related genes, such as RANK, NFATc1, cathepsin K, c-Fos, TRAP, matrix metallopeptidase-9, dendritic cell-specific transmembrane protein, ATPase H+ transporting v0 subunit d2, and osteoclast-associated receptor in RAW264.7 cells treated with RANKL. SGG and ARH extracts were found to affect the expression of NFATc1 and genes that are specific to osteoclasts during osteoclast differentiation, suggesting their potential use as functional foods or as therapeutic interventions targeting bone health.

The comparable efficacy of denosumab on bone mineral density in rheumatoid arthritis patients with postmenopausal osteoporosis: A retrospective case-control study

Little is known about differences in the therapeutic efficacy of denosumab in subjects with and without rheumatoid arthritis (RA). This study compares the changes in bone mineral density (BMD) between RA patients and controls without RA who had been treated with denosumab for 2 years for postmenopausal osteoporosis. A total of 82 RA patients and 64 controls were enrolled, who were refractory to selective estrogen receptor modulators (SERMs) or bisphosphonates and completed the treatment of denosumab 60 mg for 2 years. The efficacy of denosumab in RA patients and controls was assessed using areal BMD (aBMD) and T-score of the lumbar spine, femur neck, and total hip. A general linear model with repeated measures analysis of variance was used to determine differences in aBMD and T-score between 2 study groups. No significant differences in percent changes in aBMD and T-scores by denosumab treatment for 2 years at the lumbar spine, femur neck, and total hip were evident between RA patients and controls (P > .05 of all), except T-score of the total hip (P = .034). Denosumab treatment equally increased aBMD at the lumbar spine and T-scores at the lumbar spine and total hip between RA patients and controls without statistical differences, but RA patients showed less improvement in aBMD at the femur neck (ptime*group = 0.032) and T-scores at the femur neck and total hip than controls (ptime*group = 0.004 of both). Changes in aBMD and T-scores after denosumab treatment in RA patients were not affected by previous use of bisphosphonates or SERMs. Differences of T-score at the femur neck among previous bisphosphonate users and aBMD and T-score at the femur neck and T-scores at the total hip were evident. This study revealed that 2 years of denosumab treatment in female RA patients achieved comparable efficacy on BMD to controls at the lumbar spine, but showed somewhat insufficient improvement at the femur neck and total hip.

Rapamycin Inhibits Osteoclastogenesis and Prevents LPS-Induced Alveolar Bone Loss by Oxidative Stress Suppression

Periodontitis is a progressive inflammatory skeletal disease characterized by periodontal tissue destruction, alveolar bone resorption, and tooth loss. Chronic inflammatory response and excessive osteoclastogenesis play essential roles in periodontitis progression. Unfortunately, the pathogenesis that contributes to periodontitis remains unclear. As a specific inhibitor of the mTOR (mammalian/mechanistic target of rapamycin) signaling pathway and the most common autophagy activator, rapamycin plays a vital role in regulating various cellular processes. The present study investigated the effects of rapamycin on osteoclast (OC) formation in vitro and its effects on the rat periodontitis model. The results showed that rapamycin inhibited OC formation in a dose-dependent manner by up-regulating the Nrf2/GCLC signaling pathway, thus suppressing the intracellular redox status, as measured by 2',7'-dichlorofluorescein diacetate and MitoSOX. In addition, rather than simply increasing the autophagosome formation, rapamycin increased the autophagy flux during OC formation. Importantly, the anti-oxidative effect of rapamycin was regulated by an increase in autophagy flux, which could be attenuated by blocking autophagy with bafilomycin A1. In line with the in vitro results, rapamycin treatment attenuated alveolar bone resorption in rats with lipopolysaccharide-induced periodontitis in a dose-dependent manner, as assessed by micro-computed tomography, hematoxylin-eosin staining, and tartrate-resistant acid phosphatase staining. Besides, high-dose rapamycin treatment could reduce the serum levels of proinflammatory factors and oxidative stress in periodontitis rats. In conclusion, this study expanded our understanding of rapamycin's role in OC formation and protection from inflammatory bone diseases.

The osteocyte and its osteoclastogenic potential

The skeleton is an organ of dual functionality; on the one hand, it provides protection and structural competence. On the other hand, it participates extensively in coordinating homeostasis globally given that it is a mineral and hormonal reservoir. Bone is the only tissue in the body that goes through strategically consistent bouts of bone resorption to ensure its integrity and organismal survival in a temporally and spatially coordinated process, known as bone remodeling. Bone remodeling is directly enacted by three skeletal cell types, osteoclasts, osteoblasts, and osteocytes; these cells represent the acting force in a basic multicellular unit and ensure bone health maintenance. The osteocyte is an excellent mechanosensory cell and has been positioned as the choreographer of bone remodeling. It is, therefore, not surprising that a holistic grasp of the osteocyte entity in the bone is warranted. This review discusses osteocytogenesis and associated molecular and morphological changes and describes the osteocytic lacunocanalicular network (LCN) and its organization. We highlight new knowledge obtained from transcriptomic analyses of osteocytes and discuss the regulatory role of osteocytes in promoting osteoclastogenesis with an emphasis on the case of osteoclastogenesis in anosteocytic bones. We arrive at the conclusion that osteocytes exhibit several redundant means through which osteoclast formation can be initiated. However, whether osteocytes are true "orchestrators of bone remodeling" cannot be verified from the animal models used to study osteocyte biology in vivo. Results from studying osteocyte biology using current animal models should come with the caveat that these models are not osteocyte-specific, and conclusions from these studies should be interpreted cautiously.

Identification of Differentially Expressed Genes and Molecular Pathways Involved in Osteoclastogenesis Using RNA-seq

Osteoporosis is a disease that is characterised by reduced bone mineral density (BMD) and can be exacerbated by the excessive bone resorption of osteoclasts (OCs). Bioinformatic methods, including functional enrichment and network analysis, can provide information about the underlying molecular mechanisms that participate in the progression of osteoporosis. In this study, we harvested human OC-like cells differentiated in culture and their precursor peripheral blood mononuclear cells (PBMCs) and characterised the transcriptome of the two cell types using RNA-sequencing in order to identify differentially expressed genes. Differential gene expression analysis was performed in RStudio using the edgeR package. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to identify enriched GO terms and signalling pathways, with inter-connected regions characterised using protein-protein interaction analysis. In this study, we identified 3201 differentially expressed genes using a 5% false discovery rate; 1834 genes were upregulated, whereas 1367 genes were downregulated. We confirmed a significant upregulation of several well-established OC genes including CTSK, DCSTAMP, ACP5, MMP9, ITGB3, and ATP6V0D2. The GO analysis suggested that upregulated genes are involved in cell division, cell migration, and cell adhesion, while the KEGG pathway analysis highlighted oxidative phosphorylation, glycolysis and gluconeogenesis, lysosome, and focal adhesion pathways. This study provides new information about changes in gene expression and highlights key biological pathways involved in osteoclastogenesis.

Extracellular Release of Citrullinated Vimentin Directly Acts on Osteoclasts to Promote Bone Resorption in a Mouse Model of Periodontitis

Elevated osteoclast (OC)-mediated bone resorption, a common pathological feature between periodontitis and rheumatoid arthritis (RA), implicates a possible mutually shared pathogenesis. The autoantibody to citrullinated vimentin (CV), a representative biomarker of RA, is reported to promote osteoclastogenesis (OC-genesis). However, its effect on OC-genesis in the context of periodontitis remains to be elucidated. In an in vitro experiment, the addition of exogenous CV upregulated the development of Tartrate-resistant acid phosphatase (TRAP)-positive multinuclear OCs from mouse bone marrow cells and increased the formation of resorption pits. However, Cl-amidine, an irreversible pan-peptidyl arginine deiminase (PAD) inhibitor, suppressed the production and secretion of CV from RANKL-stimulated OC precursors, suggesting that the citrullination of vimentin occurs in OC precursors. On the other hand, the anti-vimentin neutralizing antibody suppressed in vitro Receptor activator of nuclear factor kappa-Β ligand (RANKL)-induced OC-genesis. The CV-induced upregulation of OC-genesis was abrogated by the Protein kinase C (PKC)-δ inhibitor Rottlerin, accompanied by the downmodulation of OC-genesis-related genes, including Osteoclast stimulatory transmembrane protein (OC-STAMP), TRAP and Matrix Metallopeptidase 9 (MMP9) as well as extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP)-kinase phosphorylation. Elevated levels of soluble CV and vimentin-bearing mononuclear cells were found in the bone resorption lesions of periodontitis induced in mice in the absence of an anti-CV antibody. Finally, local injection of anti-vimentin neutralizing antibody suppressed the periodontal bone loss induced in mice. Collectively, these results indicated that the extracellular release of CV promoted OC-genesis and bone resorption in periodontitis.

New Insights into Calorie Restriction Induced Bone Loss

Caloric restriction (CR) is now a popular lifestyle choice due to its ability in experimental animals to improve lifespan, reduce body weight, and lessen oxidative stress. However, more and more emerging evidence suggests this treatment requires careful consideration because of its detrimental effects on the skeletal system. Experimental and clinical studies show that CR can suppress bone growth and raise the risk of fracture, but the specific mechanisms are poorly understood. Reduced mechanical loading has long been thought to be the primary cause of weight loss-induced bone loss from calorie restriction. Despite fat loss in peripheral depots with calorie restriction, bone marrow adipose tissue (BMAT) increases, and this may play a significant role in this pathological process. Here, we update recent advances in our understanding of the effects of CR on the skeleton, the possible pathogenic role of BMAT in CR-induced bone loss, and some strategies to mitigate any potential side effects on the skeletal system.

CYLD inhibits osteoclastogenesis to ameliorate alveolar bone loss in mice with periodontitis

Periodontitis is a chronic immune inflammatory disease that can lead to the destruction and loss of the tooth-supporting apparatus. During this process, the balance between bone absorption mediated by osteoclasts and bone formation mediated by osteoblasts is damaged. Consistent with previous studies, we observed that depletion of cylindromatosis (CYLD) resulted in an osteoporotic bone phenotype. However, the effect of CYLD deficiency on periodontitis is undetermined. Here, we investigated whether CYLD affects periodontal tissue homeostasis in experimental periodontitis in Cyld knockout (KO) mice, and we explored the underlying mechanisms. Interestingly, we discovered significant alveolar bone density loss and severely reduced alveolar bone height in Cyld KO mice with experimentally induced periodontitis. We observed increased osteoclast number and activity in both the femurs and alveolar bones, accompanied by the downregulation of osteogenesis genes and upregulation of osteoclastogenesis genes of alveolar bones in ligatured Cyld KO mice. Taken together, our findings demonstrate that the deletion of CYLD in mice plays a vital role in the pathogenesis of periodontal bone loss and suggest that CYLD might exert an ameliorative effect on periodontal inflammatory responses.

Effects of green tea extract epigallocatechin-3-gallate (EGCG) on orthodontic tooth movement and root resorption in rats

OBJECTIVE

To study the effect of EGCG on tooth movement and root resorption during orthodontic treatment in rats.

METHODS

A total of thirty six male Wistar rats were randomly and equally divided into three groups: control, 50 mg/kg EGCG, and 100 mg/kg EGCG. During the experiment, the subjects were submitted to an orthodontic tooth movement (OTM) model, rats in the experimental groups were given the corresponding dose of EGCG, while rats in the control group were administrated with an equal volume of normal saline solution by gavage. After 14 days of OTM, the rats were sacrificed by transcardial perfusion. Micro-CT of rat maxillaes was taken to analyze OTM distance and root resorption. The maxillary samples were prepared as histological sections for H&E staining, tartrate-resistant acid phosphatase (TRAP) staining and immunohistochemical (IHC) staining to be observed and analyzed.

RESULTS

The OTM distance and root resorption of rats in the dosed group decreased, and the number of TRAP positive cells in their periodontium decreased significantly. The expression level of RANKL was decreased in the EGCG group compared to the control group, while that of OPG, OCN and Runx2 was increased. Effects were more pronounced in 100 mg/kg group than in 50 mg/kg group.

CONCLUSION

EGCG reduces OTM and orthodontic induced root resorption (OIRR) in rats, and is able to attenuate osteoclastogenesis on the pressure side and promote osteogenesis on the tension side.

Research progress on the role of extracellular vesicles derived from aging cells in osteoporosis

The occurrence and development of many diseases are highly associated with the aging of the body. Among them, osteoporosis (OP) is a common age-related disease that tends to occur in the elderly population and is highly related to the aging factors in the body. In the process of aging transmission, the senescence-related secretory phenotype (SASP) can convey the information about aging through the paracrine pathway and endocrine mechanism through the extracellular vesicles (EVs) connected to SASP. EVs can be used as a way of conduction to join the connection between micro-environmental aging and age-related illnesses. EVs are double-layer membranous vesicles separated or secreted from the cell membrane, which mainly include microvesicles (MVs) and exosomes. Vesicular bodies secreted by this exocrine form carry a variety of cell-derived related substances (including a variety of proteins, lipids, DNA, mRNA, miRNAs, etc). These substances are mainly concentrated in human body fluids, especially can be transported to all parts of the body with the blood circulation system, and participate in the interactions between cells. Osteoporosis is closely associated with aging and aging cells, suggesting EVs were active in this pathological process. In this article, the basic mechanisms of aging cells in the occurrence and progression of osteoporosis through EVs will be discussed, to explore the connection between aging and osteoporosis, thereby providing a new perspective on the occurrence and development as well as prevention and treatment of osteoporosis.

Molecular Basis beyond Interrelated Bone Resorption/Regeneration in Periodontal Diseases: A Concise Review

Periodontitis is the sixth most common chronic inflammatory disease, destroying the tissues supporting the teeth. There are three distinct stages in periodontitis: infection, inflammation, and tissue destruction, where each stage has its own characteristics and hence its line of treatment. Illuminating the underlying mechanisms of alveolar bone loss is vital in the treatment of periodontitis to allow for subsequent reconstruction of the periodontium. Bone cells, including osteoclasts, osteoblasts, and bone marrow stromal cells, classically were thought to control bone destruction in periodontitis. Lately, osteocytes were found to assist in inflammation-related bone remodeling besides being able to initiate physiological bone remodeling. Furthermore, mesenchymal stem cells (MSCs) either transplanted or homed exhibit highly immunosuppressive properties, such as preventing monocytes/hematopoietic precursor differentiation and downregulating excessive release of inflammatory cytokines. In the early stages of bone regeneration, an acute inflammatory response is critical for the recruitment of MSCs, controlling their migration, and their differentiation. Later during bone remodeling, the interaction and balance between proinflammatory and anti-inflammatory cytokines could regulate MSC properties, resulting in either bone formation or bone resorption. This narrative review elaborates on the important interactions between inflammatory stimuli during periodontal diseases, bone cells, MSCs, and subsequent bone regeneration or bone resorption. Understanding these concepts will open up new possibilities for promoting bone regeneration and hindering bone loss caused by periodontal diseases.