Activated T cells regulate bone loss and joint destruction in adjuvant arthritis through osteoprotegerin ligand

A remotely controlled nanotherapeutic with immunomodulatory property for MRSA-induced bone infection

Osteomyelitis is a deep bone tissue infection caused by pathogenic microorganisms, with the primary pathogen being methicillin-resistant Staphylococcus aureus (MRSA). Due to the tendency of the infection site to form biofilms that shield drugs and immune cells to kill bacteria, combined with the severe local inflammatory response causing bone tissue destruction, the treatment of osteomyelitis poses a significant challenge. Herein, we developed a remotely controlled nanotherapeutic (TLBA) with immunomodulatory to treat MRSA-induced osteomyelitis. TLBA, combined with baicalin and gold nanorods, is positively charged to actively target and penetrate biofilms. Near-infrared light (808 nm) triggers spatiotemporal, controllable drug release, while bacteria are eliminated through synergistic interaction of non-antibiotic drugs and photothermal therapy, enhancing bactericidal efficiency and minimizing drug resistance. TLBA eliminated nearly 100 % of planktonic bacteria and dispersed 90 % of biofilms under NIR light stimulation. In MRSA-induced osteomyelitis rat models, laser irradiation raised the infection site temperature to 50 °C, effectively eradicating bacteria, promoting M2 macrophage transformation, inhibiting bone inflammation, curbing bone destruction, and fostering bone tissue repair. In summary, TLBA proposes a more comprehensive treatment strategy for the two characteristic pathological changes of bacterial infection and bone tissue damage in osteomyelitis.

Pathophysiology of bone remodelling cycle: Role of immune system and lipids

Osteoporosis is the most common skeletal disease worldwide, characterized by low bone mineral density, resulting in weaker bones, and an increased risk of fragility fractures. The maintenance of bone mass relies on the precise balance between bone synthesis and resorption. The close relationship between the immune and skeletal systems, called "osteoimmunology", was coined to identify these overlapping "scientific worlds", and its function resides in the evaluation of the mutual effects of the skeletal and immune systems at the molecular and cellular levels, in both physiological and pathological states. Lipids play an essential role in skeletal metabolism and bone health. Indeed, bone marrow and its skeletal components demand a dramatic amount of daily energy to control hematopoietic turnover, acquire and maintain bone mass, and actively being involved in whole-body metabolism. Statins, the main therapeutic agents in lowering plasma cholesterol levels, are able to promote osteoblastogenesis and inhibit osteoclastogenesis. This review is meant to provide an updated overview of the pathophysiology of bone remodelling cycle, focusing on the interplay between bone, immune system and lipids. Novel therapeutic strategies for the management of osteoporosis are also discussed.

Synovial Fluid as a Crucial Component of the Joint Microenvironment in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease closely associated with synovial tissue proliferation, pannus formation in small joints such as the hands, wrists, and feet, cartilage destruction, and systemic complications such as pulmonary, cardiovascular, neurological, and skeletal muscle lesions, glucocorticoid-induced osteoporosis and infections. The importance of confirming the diagnosis and determining local activity is given to the study of synovial fluid. A deep understanding of the pathological process in the joint in RA, characterized by changes in autoreactive CD4+ T cells, B cells, macrophages, inflammatory cytokines, chemokines, and autoantibodies, has now been achieved, although much remains to be explored. This article provides an updated overview of the pathogenesis of RA, revealing even more therapeutic targets for the intra-articular pathological process.

Bone marrow adipogenic lineage precursors are the major regulator of bone resorption in adult mice

Bone resorption by osteoclasts is a critical step in bone remodeling, a process important for maintaining bone homeostasis and repairing injured bone. We previously identified a bone marrow mesenchymal subpopulation, marrow adipogenic lineage precursors (MALPs), and showed that its production of RANKL stimulates bone resorption in young mice using Adipoq-Cre. To exclude developmental defects and to investigate the role of MALPs-derived RANKL in adult bone, we generated inducible reporter mice (Adipoq-CreER Tomato) and RANKL deficient mice (Adipoq-CreER RANKLflox/flox, iCKO). Single cell-RNA sequencing data analysis and lineage tracing revealed that Adipoq+ cells contain not only MALPs but also some mesenchymal progenitors capable of osteogenic differentiation. In situ hybridization showed that RANKL mRNA is only detected in MALPs, but not in osteogenic cells. RANKL deficiency in MALPs induced at 3 months of age rapidly increased trabecular bone mass in long bones as well as vertebrae due to diminished bone resorption but had no effect on the cortical bone. Ovariectomy (OVX) induced trabecular bone loss at both sites. RANKL depletion either before OVX or at 6 weeks post OVX protected and restored trabecular bone mass. Furthermore, bone healing after drill-hole injury was delayed in iCKO mice. Together, our findings demonstrate that MALPs play a dominant role in controlling trabecular bone resorption and that RANKL from MALPs is essential for trabecular bone turnover in adult bone homeostasis, postmenopausal bone loss, and injury repair.

From death to birth: how osteocyte death promotes osteoclast formation

Bone remodeling is a dynamic and continuous process involving three components: bone formation mediated by osteoblasts, bone resorption mediated by osteoclasts, and bone formation-resorption balancing regulated by osteocytes. Excessive osteocyte death is found in various bone diseases, such as postmenopausal osteoporosis (PMOP), and osteoclasts are found increased and activated at osteocyte death sites. Currently, apart from apoptosis and necrosis as previously established, more forms of cell death are reported, including necroptosis, ferroptosis and pyroptosis. These forms of cell death play important role in the development of inflammatory diseases and bone diseases. Increasing studies have revealed that various forms of osteocyte death promote osteoclast formation via different mechanism, including actively secreting pro-inflammatory and pro-osteoclastogenic cytokines, such as tumor necrosis factor alpha (TNF-α) and receptor activator of nuclear factor-kappa B ligand (RANKL), or passively releasing pro-inflammatory damage associated molecule patterns (DAMPs), such as high mobility group box 1 (HMGB1). This review summarizes the established and potential mechanisms by which various forms of osteocyte death regulate osteoclast formation, aiming to provide better understanding of bone disease development and therapeutic target.

Quercetagetin alleviates inflammatory osteoclastogenesis and collagen antibody-induced arthritis via Nrf2 signaling and Pten/AKT/Nfatc1 axis

PURPOSE

Quercetagetin, a flavonoid derived from the natural herb Flos eriocauli, is used in traditional Chinese medicine for its fire-purging (anti-inflammation) and wind-expelling (pain-alleviating) properties. However, its potential effects concerning rheumatoid arthritis (RA) remain underexplored. This study was designed to elucidate the potential associations between Quercetagetin and RA, establishing the therapeutic potential of Quercetagetin and related mechanisms in RA treatment.

METHODS

Network pharmacology was conducted to decipher related targets and signaling pathways between Quercetagetin and RA. In vitro assays were then conducted to explore the effects of Quercetagetin on osteoclast cell behaviors and corresponding signaling pathways. In vivo study further validated the therapeutic effect of Quercetagetin in collagen antibody-induced arthritis (CAIA) mice.

RESULTS

The network pharmacological analysis indicated an intimate correlation of Quercetagetin with RA-related inflammatory osteolysis treatment. Pertaining to biological validations, 2 µM of Quercetagetin successfully inhibited LPS-driven osteoclast differentiation and function. qPCR assay and Western blot analyses denoted parallel changes in osteoclastic marker genes and proteins. Further mechanism study uncovered the effect of Quercetagetin in stimulating the Nrf2/Keap1 signaling pathway and moderating the Pten/AKT/Nfatc1 axis in osteoclasts. In vivo study revealed 40 mg/kg Quercetagetin every day could significantly relief joint destruction in CAIA mice.

CONCLUSIONS

Our study presents Quercetagetin 's therapeutic potential in treating RA, outlining its effects and potential mechanisms in suppressing LPS-induced osteoclast activity, and alleviating inflammatory bone destruction in CAIA model, thereby laying the groundwork for further translational research on Quercetagetin and Flos eriocauli in RA treatment.

Norwogonin Attenuates Inflammatory Osteolysis and Collagen-Induced Arthritis via Modulating Redox Signalling and Calcium Oscillations

Norwogonin is a flavonoid extraction derived from Scutellaria baicalensis. However, its potential mechanisms in the context of rheumatoid arthritis (RA) are unclear. This study investigates the specific effects and associated targets of Norwogonin in RA-related inflammatory osteolysis. Network pharmacology was conducted to analyse the core targets and signalling pathways of Norwogonin in RA. In vitro experiments were carried out to explore the actual effects of Norwogonin on osteoclast behaviours and related signalling mechanisms. In vivo studies further validated the therapeutic effect of Norwogonin in collagen-induced arthritis (CIA) mice. The network pharmacological analysis identified 18 shared targets between Norwogonin and RA, indicating a connection with inflammatory response and oxidoreductase activity. For biological validations, the results of in vitro experiments revealed 160 μM of Norwogonin inhibited LPS-driven osteoclast differentiation and function. The qPCR assay and Western blot analysis also disclosed consistently diminished changes to osteoclastic marker genes and proteins due to Norwogonin treatment, including those for osteoclast differentiation (Traf6, Tnfrsf11a and Nfatc1), fusion (Atp6v0d2, Dcstamp and Ocstamp) and function (Mmp9, Ctsk and Acp5). Further mechanism study revealed Norwogonin suppressed LPS-driven ROS production and calcium (Ca2+) oscillations. Also, intraperitoneal injection of 30 mg/kg Norwogonin every other day successfully mitigated clinical arthritis progression and attenuated bone destruction in the CIA model. Our study scrutinises Norwogonin's therapeutic prospects in treating RA and illustrates its inhibitory effects and potential mechanism within LPS-induced osteoclastogenesis and CIA mice, providing a basis for further translational research on Norwogonin in the treatment of RA-related inflammatory osteolysis.

Relationship between systemic inflammatory response index and bone mineral density in children and adolescents aged 8-19 years: a cross-sectional study based on NHANES 2011-2016

Objective

This study aims to investigate the relationship between the Systemic Inflammatory Response Index (SIRI) and bone mineral density (BMD) in children and adolescents aged 8-19 years.

Methods

A cross-sectional design was used, utilizing NHANES data from 2011-2016, including 3,205 participants aged 8 to 19 years. Weighted multivariable regression analysis was conducted to assess the association between SIRI and BMD at the lumbar spine, pelvis, trunk, and whole body. Additionally, smooth curve fitting was applied to examine the nonlinear relationship between SIRI and BMD, and subgroup analyses were performed to explore potential interaction effects and modifiers.

Results

SIRI was significantly positively correlated with BMD at the pelvis, trunk, and whole body (p < 0.05). After adjusting for covariates, a one-unit increase in ln(SIRI) was associated with increases in BMD of 0.018 g/cm², 0.006 g/cm², and 0.005 g/cm² for the pelvis, trunk, and whole body, respectively. Nonlinear analysis revealed a saturation effect between ln(SIRI) and BMD, with a more pronounced impact at specific threshold values. Subgroup analysis indicated that gender, age, BMI and total calcium levels modulated the relationship between SIRI and BMD.

Conclusion

SIRI is significantly associated with BMD in children and adolescents, with a positive effect on BMD at specific threshold levels. This finding suggests that SIRI may serve as a potential biomarker for assessing the risk of low bone mineral density, offering theoretical support for the prevention and intervention of bone health issues such as osteoporosis.

Clinical and Pathophysiological Tangles Between Allergy and Autoimmunity: Deconstructing an Old Dichotomic Paradigm

Allergic and autoimmune disorders are characterised by dysregulation of the immune responses to otherwise inert environmental substances and autoantigens, leading to inflammation and tissue damage. Their incidence has constantly increased in the last decades, and their co-occurrence defies current standards in patient care. For years, allergy and autoimmunity have been considered opposite conditions, with IgE and Th2 lymphocytes cascade driving canonical allergic manifestations and Th1/Th17-related pathways accounting for autoimmunity. Conversely, growing evidence suggests that these conditions not only share some common inciting triggers but also are subtended by overlapping pathogenic pathways. Permissive genetic backgrounds, along with epithelial barrier damage and changes in the microbiome, are now appreciated as common risk factors for both allergy and autoimmunity. Eosinophils and mast cells, along with autoreactive IgE, are emerging players in triggering and sustaining autoimmunity, while pharmacological modulation of B cells and Th17 responses has provided novel clues to the pathophysiology of allergy. By combining clinical and therapeutic evidence with data from mechanistic studies, this review provides a state-of-the-art update on the complex interplay between allergy and autoimmunity, deconstructing old dichotomic paradigms and offering potential clues for future research.

Osteoporosis and Rheumatoid Arthritis: Mechanisms Underlying Osteoclast Differentiation and Activation or Factors Associated with Hip Fractures

Osteoporosis is defined as a condition of increased risk of fracture due to decreased bone strength. In developed countries, the number of patients with osteoporosis and fragility fractures has been increasing in recent years due to the growing elderly population, posing a social challenge not only to fracture patients and their families but also to the social healthcare economy. Osteoporosis can be divided into two categories: primary osteoporosis caused by aging or menopause and secondary osteoporosis caused by metabolic or inflammatory diseases or drugs such as glucocorticoids. The majority of patients have primary osteoporosis, and the pathogenesis of postmenopausal osteoporosis and factors associated with fragility fractures in the elderly have been elucidated. On the other hand, rheumatoid arthritis (RA) is one of the causes of secondary osteoporosis. RA is a chronic inflammatory disease characterized by joint swelling and destruction. Most often, treatment focuses on suppressing these symptoms. However, physicians should be aware of the risk of osteoporosis in RA patients, because (1) RA is a chronic inflammatory disease, which itself can be a risk factor for osteoporosis; (2) glucocorticoids, which are sometimes administered to treat RA, can be a risk factor for osteoporosis; and (3) patients with RA are becoming older, and aging is an osteoporosis risk factor. A comprehensive understanding of the pathogenesis of osteoporosis and its fragility fractures requires elucidating the mechanisms underlying osteoclast activation, which drives their development. Furthermore, identifying the factors associated with fragility fractures is essential. This review summarizes the pathogenesis of osteoporosis, the factors associated with fragility fractures, and the associations between RA and osteoporosis development.

The p53-miR17 family-Rankl axis bridges liver-bone communication

Our study elucidates the crucial role of the liver in bone homeostasis through the p53-miR17 family (miR17-miR20/miR20-miR106/miR93-miR106)-Rankl axis. We demonstrate the enhanced hepatocyte Rankl expression in inflammaging conditions, such as aging, ovariectomized (OVX) mice, and elderly humans. Mice with hepatocyte-specific Rankl deletion exhibit significant resistance to bone mass loss associated with aging, lipopolysaccharide (LPS)-induced inflammation, or estrogen deficiency, compared with controls. Our study highlights hepatocytes as the primary source of Rankl in the liver and serum under these conditions. We identify the p53-miR17 family axis as a crucial regulator for hepatocyte Rankl expression, with p53 inhibiting the miR17 family transcription. Through bioinformatics analysis and in vitro validation, we identify Rankl mRNA as a direct target of the miR17 family. Targeting this axis via CasRx-mediated mRNA editing or miRNA interference significantly attenuates bone mass loss in mice. Our investigation underscores the pivotal significance and therapeutic potential of modulating the p53-miR17 family-Rankl axis in the treatment of inflammaging-associated osteoporosis.

Innate immune response to bone fracture healing

The field of osteoimmunology has primarily focused on fracture healing in isolated musculoskeletal injuries. The innate immune system is the initial response to fracture, with inflammatory macrophages, cytokines, and neutrophils arriving first at the fracture hematoma, followed by an anti-inflammatory phase to begin the process of new bone formation. This review aims to first discuss the current literature and knowledge gaps on the immune responses governing single fracture healing by encompassing the individual role of macrophages, neutrophils, cytokines, mesenchymal stem cells, bone cells, and other immune cells. This paper discusses the interactive effects of these cellular responses underscoring the field of osteoimmunology. The critical role of the metabolic environment in guiding the immune system properties will be highlighted along with some effective therapeutics for fracture healing in the context of osteoimmunology. However, compared to isolated fractures, which frequently heal well, long bone fractures in over 30 % of polytrauma patients exhibit impaired healing. Clinical evidence suggests there may be distinct physiologic and inflammatory pathways altered in polytrauma resulting in nonunion. Nonunion is associated with worse patient outcomes and increased societal healthcare costs. The dysregulated immunomodulatory/inflammatory response seen in polytrauma may lead to this increased nonunion rate. This paper will investigate the differences in immune response between isolated and polytrauma fractures. Finally, future directions for fracture studies are explored with consideration of the emerging roles of newly discovered immune cell functions in fracture healing, the existing challenges and conflicting results in the field, the translational potential of these studies in clinic, and the more complex nature of polytrauma fractures that can alter cell functions in different tissues.

Beta-adrenergic receptor antagonist propranolol prevents bisphosphonate-related osteonecrosis of the jaw by promoting osteogenesis

Background/purpose

Bisphosphonate-related osteonecrosis of the jaw (BRONJ), a complication arising from the use of bisphosphonates (BPs), inflicts long-term suffering on patients. Currently, there is still a lack of effective treatments. This study aimed to explore the preventive effects of propranolol (PRO) on BRONJ in vitro and in vivo, given PRO's potential in bone health enhancement.

Materials and methods

In vitro, effect of PRO on zoledronic acid (ZA)-pretreated bone marrow mesenchymal stem cells (BMSCs) was detected by cell counting kit-8, alkaline phosphatase (ALP) staining, alizarin red staining, real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot. In vivo, forty mice were divided into four groups: control, ZA, PRO, and ZA-PRO. The maxillary extraction sockets sides were analyzed with micro-CT and histomorphometry. Hematoxylin-eosin (H&E), Masson staining, immunofluorescence staining of ALP, bone morphogenetic protein 2 (BMP2), runt-related transcription factor 2 (RUNX2) and TUNEL staining were performed.

Results

PRO increased proliferation and osteogenic differentiation of BMSCs. PRO stimulated bone formation and facilitated the healing process in zoledronic acid-induced osteonecrosis of jaw in mouse model. Compared with ZA group, control and PRO group showed more BMP2+, RUNX2+, and ALP+ cells (P < 0.05). However, PRO rescued the decreased expression of ALP, RUNX2, BMP2 due to ZA and decreased the expression of TUNEL (P < 0.05).

Conclusion

The findings suggest that propranolol may offer a promising preventive strategy against BRONJ by enhancing bone regeneration. This research contributes to the understanding of the pathogenesis of BRONJ and opens avenues for potential treatments of BRONJ focusing on β-adrenergic signaling.

Global Highly Cited Publication Trends and Research Hotspots in Osteoporosis and Bone Metabolic Cells: A Bibliometric and Visualization Analysis from 2013 to 2023

BACKGROUND

Bone metabolic diseases such as osteoporosis are caused by disruption of the metabolic balance between osteoblasts and osteoclasts. Thousands of papers have been published on osteoporosis and bone metabolizing cells. The purpose of this study is to draw the publication trend of highly cited literature in this field through bibliometrics and to explore the research hotspot analysis.

OBJECTIVE

This paper provides a comprehensive analysis of the impact of countries/regions, research institutions, authors, keywords, relevant journals, and references in the field of osteoporosis and bone metabolic cells research, with a specific focus on the theme of "Osteoporosis and bone metabolic cells". Furthermore, utilizing bibliometric methods, the study aims to offer valuable insights and references for future research endeavors, as well as clinical prevention and treatment strategies in this domain.

METHODS

The Web of Science (WOS) Core Collection database was examined in order to identify articles with high citation counts from 2013 to 31 October 2023. The citation counts, authors, year of publication, source, journal, geographical origin, subject, article type, and level of evidence were further analyzed using the R bibliometric package. The VOSviewer software was utilized to visualize word co-occurrence in a total of 251 articles.

RESULTS

Our search strategy included 251 highly cited articles published between 2013 and 2023 in the field of osteoporosis and bone metabolic cells. The number of publications in this field remains consistently high, indicating ongoing research interest. Notably, the United States has made significant achievements and contributions in this area. Xie Hui, Cao Xu, and Goodman, Stewart are among the main contributors to these advancements. Nature medicine has the highest journal impact factor of 82.9, highlighting its prominence. The journal of bone and mineral research ranks first with 1,322 citations. Keyword research topics in this field include osteoclast differentiation, osteoblast differentiation, and mesenchymal stem cells. Through citation analysis, we found that 195 articles have been cited more than 100 times, demonstrating their significance and impact.

CONCLUSION

This study analyzed the relationship between osteoporosis and bone metabolic cells using a bibliometric method. The results of these analyses can help researchers gain a more direct and scientific understanding of trends in the field. Additionally, it can provide guidance in identifying hot research directions and offer new ideas for the prevention and treatment of osteoporosis.

Importance of trace elements in the immunometabolic health of people living with HIV/AIDS: a literature review

Trace elements (TEs) are essential for human health and for maintaining immune responses against potentially aggressive pathogens, such as the human immunodeficiency virus (HIV). During the infectious process, the body needs greater amounts of TEs in order to coordinate an efficient immune response to combat the invading agent, a condition that reflects in lymphocyte proliferation and activation of the antioxidant defense system of neutrophils and macrophages. Thus, during the progression phase of a viral infection, immunomodulation of TEs such as iron, zinc, chromium, magnesium, selenium, copper, calcium, and manganese occurs, can lead to immunosuppression and increased oxidative stress. Furthermore, the adverse effects caused by the use of antiretroviral therapy (ART) trigger nutritional disorders and metabolic alterations that contribute to deficiencies in TEs, associated with compromised immune function. Therefore, this narrative literature review aims to contribute as a teaching tool on the TEs involved in the pathogenesis of HIV, by reviewing the role of TEs in the immunometabolic health of people living with HIV/AIDS.

Asymmetrical Damage of the Wrist Joint Induces Lateralized Cortical Bone Loss in the Metacarpal Diaphysis in Patients with Rheumatoid Arthritis

Background/Objectives: Osteoporosis is common in rheumatoid arthritis (RA), occurring either systemically or locally around inflamed joints. Decreased metacarpal bone density is a known marker of RA progression and hand function impairment. Although RA is generally characterized by symmetrical arthritis, some patients exhibit asymmetrical joint involvement. This study investigates the frequency of unilateral metacarpal bone density reduction in RA patients and aims to identify associated factors. Methods: This study included 143 RA patients (107 females, mean age 62.4 yrs., mean disease duration 11.1 yrs.). Bilateral hand X-rays were used to measure the cortical thickness rate (CTR) of the 2nd to 4th metacarpals. Unilateral bone density reduction was defined as a thin-to-thick-side CTR ratio (CTRR) < 0.8. Associations between CTR reduction and unilateral wrist joint damage (WJD) were analyzed. Results: Unilateral CTR reduction (CTRR < 0.8) was observed in 16.8% of patients, significantly associated with unilateral WJD. Among patients with unilateral WJD, 50.0% showed CTRR lateral (+) compared to 10.1% without unilateral WJD (p < 0.01). ANCOVA revealed significant effects of WJD laterality on CTRR, with an interaction effect showing greater CTRR laterality when thin-side WJD was present without thick-side WJD. Post-biologic treatment, CTR values decreased in both hands, indicating no improvement in bone density reduction. Conclusions: Approximately 17% of RA patients exhibited unilateral relative metacarpal bone density reduction, closely associated with unilateral WJD. This first detailed report on bone density laterality in RA underscores the need for early intervention and rehabilitation strategies in RA patients with hand involvement.

Elevated IL-6 Expression in Autologous Adipose-Derived Stem Cells Regulates RANKL Mediated Inflammation in Osteoarthritis

Interleukin-6 (IL-6) expression in mesenchymal stem cells (MSCs) has been shown to play a pivotal role in modulating cartilage regeneration and immune responses, particularly in the context of diseases that involve both degenerative processes and inflammation, such as osteoarthritis (OA). However, the precise mechanism through which IL-6 and other immune-regulatory factors influence the therapeutic efficacy of autologous adipose-derived stem cells (ASCs) transplantation in OA treatment remains to be fully elucidated. This study aims to investigate the relationship between IL-6 expression in autologous ASCs isolated from OA patients and their impact on immune modulation, particularly focusing on the regulation of Receptor Activator of Nuclear factor Kappa-Β Ligand (RANKL), a key mediator of immune-driven cartilage degradation in OA. Autologous ASCs were isolated from the stromal vascular fraction (SVF) of adipose tissue obtained from 22 OA patients. The isolated ASCs were cultured and characterized using reverse transcription polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), and flow cytometry to the phenotype and immune regulatory factors of MSCs. Based on IL-6 expression levels, ASCs were divided into high and low IL-6 expression groups. These groups were then co-cultured with activated peripheral blood mononuclear cells (PBMCs) to evaluate their immune-modulatory capacity, including the induction of regulatory T cells, inhibition of immune cell proliferation, and regulation of key cytokines, such as interferon-gamma (IFN-γ). Additionally, RANKL expression, a critical factor in osteoclastogenesis and cartilage degradation, was assessed in both ASC groups. High IL-6-expressing ASCs demonstrated a significantly greater capacity to inhibit immune cell proliferation and IFN-γ production compared to their low IL-6-expressing counterparts under co-culture conditions. Moreover, the group of ASCs with high IL-6 expression showed a marked reduction in RANKL expression, suggesting enhanced potential to control osteoclast activity and subsequent cartilage defect in OA. Conclusion: Autologous ASCs with elevated IL-6 expression exhibit enhanced immunomodulatory properties, particularly in regulating over-activated immune response and reducing osteoclastogenesis through RANKL suppression. These findings indicate that selecting ASCs based on IL-6 expression could enhance the therapeutic efficacy of ASC-based treatments for OA by mitigating immune-driven joint inflammation and cartilage degradation, potentially slowing disease progression.

Unraveling the Intricacies of OPG/RANKL/RANK Biology and Its Implications in Neurological Disorders-A Comprehensive Literature Review

The OPG/RANKL/RANK framework, along with its specific receptors, plays a crucial role in bone remodeling and the functioning of the central nervous system (CNS) and associated disorders. Recent research and investigations provide evidence that the components of osteoprotegerin (OPG), receptor activator of NF-kB ligand (RANKL), and receptor activator of NF-kB (RANK) are expressed in the CNS. The CNS structure encompasses cells involved in neuroinflammation, including local macrophages, inflammatory cells, and microglia that cross the blood-brain barrier. The OPG/RANKL/RANK trio modulates the neuroinflammatory response based on the molecular context. The levels of OPG/RANKL/RANK components can serve as biomarkers in the blood and cerebrospinal fluid. They act as neuroprotectants following brain injuries and also participate in the regulation of body weight, internal body temperature, brain ischemia, autoimmune encephalopathy, and energy metabolism. Although the OPG/RANKL/RANK system is primarily known for its role in bone remodeling, further exploring deeper into its multifunctional nature can uncover new functions and novel drug targets for diseases not previously associated with OPG/RANKL/RANK signaling.

Osteoimmunology in bone malignancies: a symphony with evil

Bone marrow is pivotal for normal hematopoiesis and immune responses, yet it is often compromised by malignancies. The bone microenvironment (BME), composed of bone and immune cells, maintains skeletal integrity and blood production. The emergence of primary or metastatic tumors in the skeletal system results in severe complications and contributes significantly to cancer-related mortality. These tumors set off a series of interactions among cancer, bone, and immune cells, and disrupt the BME locally or distantly. However, the drivers, participants, and underlying molecules of these interactions are not fully understood. This review explores the crosstalk between bone metabolism and immune responses, synthesizing current knowledge on the intersection of cancer and osteoimmune biology. It outlines how bone marrow immune cells can either facilitate or hinder tumor progression by interacting with bone cells and pinpoints the molecules responsible for immunosuppression within bone tumors. Moreover, it discusses how primary tumors remotely alter the BME, leading to systemic immune suppression in cancer patients. This knowledge provides critical rationales for emerging immunotherapies in the treatment of bone-related tumors. Taken together, by summarizing the intricate relationship between tumor cells and the BME, this review aims to deepen the understanding of the diversity, complexity, and dynamics at play during bone tumor progression. Ultimately, it highlights the potential of targeting bone-tumor interactions to correct aberrant immune functions, thereby inhibiting tumor growth and metastasis.

Irilin D suppresses RANKL-induced osteoclastogenesis and prevents inflammation-induced bone loss by disrupting the NF-κB and MAPK signaling pathways

Excessive activity of osteoclasts(OCs) lead to bone resorption in chronic inflammatory conditions. The use of natural compounds to target OCs offers significant promise in the treatment or prevention of OC-associated diseases. Irilin D (IRD), a natural isoflavone derived from Belamcanda chinensis (L.) DC., has potential effects on OC differentiation both in vitro and in vivo that have yet to be thoroughly explored. In our study, we found that IRD inhibited receptor activator of nuclear factor-κB ligand (RANKL)-induced OC differentiation, actin ring formation, and bone resorption in vitro without compromising cell viability. However, IRD did not exhibit anti-inflammatory effects in lipopolysaccharide (LPS)-stimulated macrophages. Furthermore, IRD reduced LPS-induced inflammatory bone loss by blocking osteoclastogenesis in a mouse model. Mechanistically, IRD disrupted RANKL-induced activation of mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB), leading to the inhibition of c-Fos and nuclear factor of activated T cells cytoplasmic 1 (NFATc1) activation. We also demonstrated that IRD inhibited RANKL-induced osteoclastic NFATc1 target genes, including DC-STAMP, ACP5, and CtsK. Our results indicate that IRD mitigates LPS-induced inflammatory bone resorption in mice by inhibiting RANKL-activated MAPKs and NF-κB signaling pathways, suggesting its potential as a natural isoflavone for preventing or treating OC-associated diseases.

Quantum dots for bone tissue engineering

In confronting the global prevalence of bone-related disorders, bone tissue engineering (BTE) has developed into a critical discipline, seeking innovative materials to revolutionize treatment paradigms. Quantum dots (QDs), nanoscale semiconductor particles with tunable optical properties, are at the cutting edge of improving bone regeneration. This comprehensive review delves into the multifaceted roles that QDs play within the realm of BTE, emphasizing their potential to not only revolutionize imaging but also to osteogenesis, drug delivery, antimicrobial strategies and phototherapy. The customizable nature of QDs, attributed to their size-dependent optical and electronic properties, has been leveraged to develop precise imaging modalities, enabling the visualization of bone growth and scaffold integration at an unprecedented resolution. Their nanoscopic scale facilitates targeted drug delivery systems, ensuring the localized release of therapeutics. QDs also possess the potential to combat infections at bone defect sites, preventing and improving bacterial infections. Additionally, they can be used in phototherapy to stimulate important bone repair processes and work well with the immune system to improve the overall healing environment. In combination with current trendy artificial intelligence (AI) technology, the development of bone organoids can also be combined with QDs. While QDs demonstrate considerable promise in BTE, the transition from laboratory research to clinical application is fraught with challenges. Concerns regarding the biocompatibility, long-term stability of QDs within the biological environment, and the cost-effectiveness of their production pose significant hurdles to their clinical adoption. This review summarizes the potential of QDs in BTE and highlights the challenges that lie ahead. By overcoming these obstacles, more effective, efficient, and personalized bone regeneration strategies will emerge, offering new hope for patients suffering from debilitating bone diseases.

IRE1α pathway: A potential bone metabolism mediator

Osteoblasts and osteoclasts collaborate in bone metabolism, facilitating bone development, maintaining normal bone density and strength, and aiding in the repair of pathological damage. Endoplasmic reticulum stress (ERS) can disrupt the intracellular equilibrium between osteoclast and osteoblast, resulting in dysfunctional bone metabolism. The inositol-requiring enzyme-1α (IRE1α) pathway-the most conservative unfolded protein response pathway activated by ERS-is crucial in regulating cell metabolism. This involvement encompasses functions such as inflammation, autophagy, and apoptosis. Many studies have highlighted the potential roles of the IRE1α pathway in osteoblasts, chondrocytes, and osteoclasts and its implication in certain bone-related diseases. These findings suggest that it may serve as a mediator for bone metabolism. However, relevant reviews on the role of the IRE1α pathway in bone metabolism remain unavailable. Therefore, this review aims to explore recent research that elucidated the intricate roles of the IRE1α pathway in bone metabolism, specifically in osteogenesis, chondrogenesis, osteoclastogenesis, and osteo-immunology. The findings may provide novel insights into regulating bone metabolism and treating bone-related diseases.

The role of Th/Treg immune cells in osteoarthritis

Osteoarthritis (OA) is a prevalent clinical condition affecting the entire joint, characterized by its multifactorial etiology and complex pathophysiology. The onset of OA is linked to inflammatory mediators produced by the synovium, cartilage, and subchondral bone, all of which are closely tied to cartilage degradation. Consequently, OA may also be viewed as a systemic inflammatory disorder. Emerging studies have underscored the significance of T cells in the development of OA. Notably, imbalances in Th1/Th2 and Th17/Treg immune cells may play a crucial role in the pathogenesis of OA. This review aims to compile recent advancements in understanding the role of T cells and their Th/Treg subsets in OA, examines the immune alterations and contributions of Th/Treg cells to OA progression, and proposes novel directions for future research, including potential therapeutic strategies for OA.

Bone marrow adipogenic lineage precursors are the major regulator of bone resorption in adult mice

Bone resorption by osteoclasts is a critical step in bone remodeling, a process important for maintaining bone homeostasis and repairing injured bone. We previously identified a bone marrow mesenchymal subpopulation, marrow adipogenic lineage precursors (MALPs), and showed that its production of RANKL stimulates bone resorption in young mice using Adipoq-Cre. To exclude developmental defects and to investigate the role of MALPs-derived RANKL in adult bone, we generated inducible reporter mice (Adipoq-CreER Tomato) and RANKL deficient mice (Adipoq-CreER RANKLflox/flox, iCKO). Single cell-RNA sequencing data analysis, lineage tracing, and in situ hybridization revealed that Adipoq+ cells contain not only MALPs but also late mesenchymal progenitors capable of osteogenic differentiation. However, RANKLmRNA was only detected in MALPs, but not in osteogenic cells. RANKL deficiency in MALPs induced at 3 months of age rapidly increased trabecular bone mass in long bones as well as vertebrae within 1 month due to diminished bone resorption but had no effect on the cortical bone. Ovariectomy (OVX) induced trabecular bone loss at both sites. RANKL depletion either before OVX or at 6 weeks post OVX protected and restored trabecular bone mass. Furthermore, bone healing after drill-hole injury was delayed in iCKO mice. Together, our findings demonstrate that MALPs play a dominant role in controlling trabecular bone resorption and that RANKL from MALPs is essential for trabecular bone turnover in adult bone homeostasis, postmenopausal bone loss, and injury repair.

Microbiota-bone axis in ageing-related bone diseases

Bone homeostasis in physiology depends on the balance between bone formation and resorption, and in pathology, this homeostasis is susceptible to disruption by different influences, especially under ageing condition. Gut microbiota has been recognized as a crucial factor in regulating host health. Numerous studies have demonstrated a significant association between gut microbiota and bone metabolism through host-microbiota crosstalk, and gut microbiota is even an important factor in the pathogenesis of bone metabolism-related diseases that cannot be ignored. This review explores the interplay between gut microbiota and bone metabolism, focusing on the roles of gut microbiota in bone ageing and aging-related bone diseases, including osteoporosis, fragility fracture repair, osteoarthritis, and spinal degeneration from different perspectives. The impact of gut microbiota on bone metabolism during aging through modification of endocrinology system, immune system and gut microbiota metabolites are summarized, facilitating a better grasp of the pathogenesis of aging-related bone metabolic diseases. This review offers innovative insights into targeting the gut microbiota for the treatment of bone ageing-related diseases as a clinical therapeutic strategy.

Exploring the impact of osteoprotegerin on osteoclast and precursor fusion: Mechanisms and modulation by ATP

Osteoclast (OC) differentiation, vital for bone resorption, depends on osteoclast and precursor fusion. Osteoprotegerin (OPG) inhibits osteoclast differentiation. OPG's influence on fusion and mechanisms is unclear. Osteoclasts and precursors were treated with OPG alone or with ATP. OPG significantly reduced OC number, area and motility and ATP mitigated OPG's inhibition. However, OPG hardly affected the motility of precusors. OPG downregulated fusion-related molecules (CD44, CD47, DC-STAMP, ATP6V0D2) in osteoclasts, reducing only CD47 in precursors. OPG reduced Connexin43 phosphorylated forms (P1 and P2) in osteoclasts, affecting only P2 in precursors. OPG disrupted subcellular localization of CD44, CD47, DC-STAMP, ATP6V0D2, and Connexin43 in both cell types. Findings underscore OPG's multifaceted impact, inhibiting multinucleated osteoclast and mononuclear precursor fusion through distinct molecular mechanisms. Notably, ATP mitigates OPG's inhibitory effect, suggesting a potential regulatory role for the ATP signaling pathway. This study enhances understanding of intricate processes in osteoclast differentiation and fusion, offering insights into potential therapeutic targets for abnormal bone metabolism.

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.

Osteoclasts and osteoarthritis: Novel intervention targets and therapeutic potentials during aging

Osteoarthritis (OA), a chronic degenerative joint disease, is highly prevalent among the aging population, and often leads to joint pain, disability, and a diminished quality of life. Although considerable research has been conducted, the precise molecular mechanisms propelling OA pathogenesis continue to be elusive, thereby impeding the development of effective therapeutics. Notably, recent studies have revealed subchondral bone lesions precede cartilage degeneration in the early stage of OA. This development is marked by escalated osteoclast-mediated bone resorption, subsequent imbalances in bone metabolism, accelerated bone turnover, and a decrease in bone volume, thereby contributing significantly to the pathological changes. While the role of aging hallmarks in OA has been extensively elucidated from the perspective of chondrocytes, their connection with osteoclasts is not yet fully understood. There is compelling evidence to suggest that age-related abnormalities such as epigenetic alterations, proteostasis network disruption, cellular senescence, and mitochondrial dysfunction, can stimulate osteoclast activity. This review intends to systematically discuss how aging hallmarks contribute to OA pathogenesis, placing particular emphasis on the age-induced shifts in osteoclast activity. It also aims to stimulate future studies probing into the pathological mechanisms and therapeutic approaches targeting osteoclasts in OA during aging.

Validating core therapeutic targets for osteoporosis treatment based on integrating network pharmacology and informatics

OBJECTIVE

Our goal was to find metabolism-related lncRNAs that were associated with osteoporosis (OP) and construct a model for predicting OP progression using these lncRNAs.

METHODS

The GEO database was employed to obtain gene expression profiles. The WGCNA technique and differential expression analysis were used to identify hypoxia-related lncRNAs. A Lasso regression model was applied to select 25 hypoxia-related genes, from which a classification model was created. Its robust classification performance was confirmed with an area under the ROC curve close to 1, as verified on the validation set. Concurrently, we constructed a ceRNA network based on these genes to unveil potential regulatory processes. Biologically active compounds of STZYD were identified using the Traditional Chinese Medicine System Pharmacology Database and Analysis Platform (TCMSP) database. BATMAN was used to identify its targets, and we obtained OP-related genes from Malacards and DisGeNET, followed by identifying intersection genes with metabolism-related genes. A pharmacological network was then constructed based on the intersecting genes. The pharmacological network was further integrated with the ceRNA network, resulting in the creation of a comprehensive network that encompasses herb-active components, pathways, lncRNAs, miRNAs, and targets. Expression levels of hypoxia-related lncRNAs in mononuclear cells isolated from peripheral blood of OP and normal patients were subsequently validated using quantitative real-time PCR (qRT-PCR). Protein levels of RUNX2 were determined through a western blot assay.

RESULTS

CBFB, GLO1, NFKB2 and PIK3CA were identified as central therapeutic targets, and ADD3-AS1, DTX2P1-UPK3BP1-PMS2P11, TTTY1B, ZNNT1 and LINC00623 were identified as core lncRNAs.

CONCLUSIONS

Our work uncovers a possible therapeutic mechanism for STZYD, providing a potential therapeutic target for OP. In addition, a prediction model of metabolism-related lncRNAs of OP progression was constructed to provide a reference for the diagnosis of OP patients.

Artesunate-loaded thermosensitive chitosan hydrogel promotes osteogenesis of maxillary tooth extraction through regulating T lymphocytes in type 2 diabetic rats

BACKGROUND

Type 2 diabetes mellitus (T2DM) causes severe bone loss after tooth extraction as a hyperglycemic environment causes aberrant bone homeostasis. Artesunate (ART) is known to possess anti-inflammation and osteogenic properties. However, its osteogenesis property in alveolar bone remains unclear. This study aimed to explore the osteogenic and immunoregulatory effects of artesunate-loaded thermosensitive chitosan hydrogel (ART-loaded TCH) on maxilla tooth extraction in T2DM rats.

METHODS

T2DM rats were induced by a high-fat diet and streptozotocin. Different concentrations of ART-loaded TCH were applied in tooth extraction sockets. Bone loss and the expression of osteogenic regulatory factors (OPG, ALP, RANK) were evaluated. The immunoregulatory effects of ART-loaded TCH were observed through detecting the infiltration of T lymphocytes and their cytokines. The underlying mechanisms were explored.

RESULTS

Results showed that the 150 mg/ml ART-loaded TCH group significantly ameliorated maxilla bone height and bone mineral density when compared with the T2DM group (p < 0.05). It also improved the expression of OPG, ALP, and RANK. Although the alteration of CD4+ T, CD8+ T, and CD4+:CD8+ T ratio has no significant difference among groups, the release of Th1 and Th2 in the 150 mg/ml ART-loaded TCH group has been significantly regulated than in the T2DM group (p < 0.05). Besides, ART-loaded TCH treatment inhibited the expression of p38 MAPK and ERK1 in T2DM maxilla.

CONCLUSIONS

Therefore, the results indicated that 150 mg/ml ART-loaded TCH could be an effective method to prevent bone loss in T2DM tooth extraction rats by modulating the immunoregulation of Th1 and Th2 and the MAPK signaling pathway.

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.

Osteoimmunology: The Crosstalk between T Cells, B Cells, and Osteoclasts in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an ongoing inflammatory condition that affects the joints and can lead to severe damage to cartilage and bones, resulting in significant disability. This condition occurs when the immune system becomes overactive, causing osteoclasts, cells responsible for breaking down bone, to become more active than necessary, leading to bone breakdown. RA disrupts the equilibrium between osteoclasts and osteoblasts, resulting in serious complications such as localized bone erosion, weakened bones surrounding the joints, and even widespread osteoporosis. Antibodies against the receptor activator of nuclear factor-κB ligand (RANKL), a crucial stimulator of osteoclast differentiation, have shown great effectiveness both in laboratory settings and actual patient cases. Researchers are increasingly focusing on osteoclasts as significant contributors to bone erosion in RA. Given that RA involves an overactive immune system, T cells and B cells play a pivotal role by intensifying the immune response. The imbalance between Th17 cells and Treg cells, premature aging of T cells, and excessive production of antibodies by B cells not only exacerbate inflammation but also accelerate bone destruction. Understanding the connection between the immune system and osteoclasts is crucial for comprehending the impact of RA on bone health. By delving into the immune mechanisms that lead to joint damage, exploring the interactions between the immune system and osteoclasts, and investigating new biomarkers for RA, we can significantly improve early diagnosis, treatment, and prognosis of this condition.

Oral microbiota-host interaction: the chief culprit of alveolar bone resorption

There exists a bidirectional relationship between oral health and general well-being, with an imbalance in oral symbiotic flora posing a threat to overall human health. Disruptions in the commensal flora can lead to oral diseases, while systemic illnesses can also impact the oral cavity, resulting in the development of oral diseases and disorders. Porphyromonas gingivalis and Fusobacterium nucleatum, known as pathogenic bacteria associated with periodontitis, play a crucial role in linking periodontitis to accompanying systemic diseases. In periodontal tissues, these bacteria, along with their virulence factors, can excessively activate the host immune system through local diffusion, lymphatic circulation, and blood transmission. This immune response disruption contributes to an imbalance in osteoimmune mechanisms, alveolar bone resorption, and potential systemic inflammation. To restore local homeostasis, a deeper understanding of microbiota-host interactions and the immune network phenotype in local tissues is imperative. Defining the immune network phenotype in periodontal tissues offers a promising avenue for investigating the complex characteristics of oral plaque biofilms and exploring the potential relationship between periodontitis and associated systemic diseases. This review aims to provide an overview of the mechanisms underlying Porphyromonas gingivalis- and Fusobacterium nucleatum-induced alveolar bone resorption, as well as the immunophenotypes observed in host periodontal tissues during pathological conditions.

Distinct cross talk of IL-17 & TGF-β with the immature CD11c+ TRAF6(-/-) -null myeloid dendritic cell-derived osteoclast precursor (mDDOCp) may engage signaling toward an alternative pathway of osteoclastogenesis for arthritic bone loss in vivo

BACKGROUND

Dendritic cells (DCs), though borne heterogeneous, are the most potent antigen-presenting cells, whose critical functions include triggering antigen-specific naïve T-cell responses and fine-tuning the innate versus adaptive immunity at the osteo-immune and/or mucosal mesenchyme interface. We previously reported that immature myeloid-CD11c+ DCs/mDCs may act like osteoclast (OC) precursors (OCp/mDDOCp) capable of developing into functional OCs via an alternative pathway of inflammation-induced osteoclastogenesis; however, what are their contribution and signaling interactions with key osteotropic cytokines (i.e., interleukin-17 [IL-17] and transforming growth factor-β [TGF-β]) to bearing such inflammatory bone loss in vivo remain unclear to date.

METHODS

Herein, we employed mature adult bone marrow-reconstituted C57BL/6 TRAF6(-/-) -null chimeras without the classical monocyte/macrophage (Mo/Mϕ)-derived OCs to address their potential contribution to OCp/mDDOCp-mediated osteoclastogenesis in the chicken type-II-collagen (CC-II)-induced joint inflammation versus arthritic bone loss and parallel associations with the double-positive CD11c+ TRAP+ TRAF6-null(-/-)  DC-like OCs detected in vivo via the quantitative dual-immunohistochemistry and digital histomorphometry for analyses.

RESULTS

The resulting findings revealed the unrecognized novel insight that (i) immature myeloid-CD11c+ TRAF6(-/-) TRAP+ DC-like OCs were involved, co-localized, and strongly associated with joint inflammation and bone loss, independent of the Mo/Mϕ-derived classical OCs, in CC-II-immunized TRAF6(-/-) -null chimeras, and (ii) the osteotropic IL-17 may engage distinct crosstalk with CD11c+ mDCs/mDDOCp before developing the CD11c+ TRAP+ TRAF6(-/-) OCs via a TGF-β-dependent interaction toward inflammation-induced arthritic bone loss in vivo.

CONCLUSION

These results confirm and substantiate the validity of TRAF6(-/-) -null chimeras to address the significance of immature mCD11c+ TRAP+ DC-like OCs/mDDOCp subset for an alternative pathway of arthritic bone loss in vivo. Such CD11c+ mDCs/mDDOCp-associated osteoclastogenesis through the step-wise twist-in-turns osteo-immune cross talks are thereby theme highlighted to depict a summative re-visitation proposed.

The impact of arthritogenic viruses in oral tissues

Arthritis and periodontitis are inflammatory diseases that share several immunopathogenic features. The expansion in the study of virus-induced arthritis has shed light on how this condition could impact other parts of the human body, including the mouth. Viral arthritis is an inflammatory joint disease caused by several viruses, most notably the alphaviruses Chikungunya virus (CHIKV), Sindbis virus (SINV), Ross River virus (RRV), Mayaro virus (MAYV), and O'nyong'nyong virus (ONNV). These viruses can induce an upsurge of matrix metalloproteinases and immune-inflammatory mediators such as Interleukin-6 (IL6), IL-1β, tumor necrosis factor, chemokine ligand 2, and receptor activator of nuclear factor kappa-B ligand in the joint and serum of infected individuals. This can lead to the influx of inflammatory cells to the joints and associated muscles as well as osteoclast activation and differentiation, culminating in clinical signs of swelling, pain, and bone resorption. Moreover, several data indicate that these viral infections can affect other sites of the body, including the mouth. The human oral cavity is a rich and diverse microbial ecosystem, and viral infection can disrupt the balance of microbial species, causing local dysbiosis. Such events can result in oral mucosal damage and gingival bleeding, which are indicative of periodontitis. Additionally, infection by RRV, CHIKV, SINV, MAYV, or ONNV can trigger the formation of osteoclasts and upregulate pro-osteoclastogenic inflammatory mediators, interfering with osteoclast activation. As a result, these viruses may be linked to systemic conditions, including oral manifestations. Therefore, this review focuses on the involvement of alphavirus infections in joint and oral health, acting as potential agents associated with oral mucosal inflammation and alveolar bone loss. The findings of this review demonstrate how alphavirus infections could be linked to the comorbidity between arthritis and periodontitis and may provide a better understanding of potential therapeutic management for both conditions.

Bioactives and their roles in bone metabolism of osteoarthritis: evidence and mechanisms on gut-bone axis

Bioactives significantly modify and maintain human health. Available data suggest that Bioactives might play a beneficial role in chronic inflammatory diseases. Although promised, defining their mechanisms and opting to weigh their benefits and limitations is imperative. Detailed mechanisms by which critical Bioactives, including probiotics and prebiotics such as dietary lipids (DHA, EPA, alpha LA), vitamin D, polysaccharides (fructooligosaccharide), polyphenols (curcumin, resveratrol, and capsaicin) potentially modulate inflammation and bone metabolism is limited. Certain dietary bioactive significantly impact the gut microbiota, immune system, and pain response via the gut-immune-bone axis. This narrative review highlights a recent update on mechanistic evidence that bioactive is demonstrated demonstrated to reduce osteoarthritis pathophysiology.

Complex Spatio-Temporal Interplay of Distinct Immune and Bone Cell Subsets during Bone Fracture Healing

BACKGROUND

The healing of a bone injury is a highly complex process involving a multitude of different tissue and cell types, including immune cells, which play a major role in the initiation and progression of bone regeneration.

METHODS

We histologically analyzed the spatio-temporal occurrence of cells of the innate immune system (macrophages), the adaptive immune system (B and T lymphocytes), and bone cells (osteoblasts and osteoclasts) in the fracture area of a femoral osteotomy over the healing time. This study was performed in a bone osteotomy gap mouse model. We also investigated two key challenges of successful bone regeneration: hypoxia and revascularization.

RESULTS

Macrophages were present in and around the fracture gap throughout the entire healing period. The switch from initially pro-inflammatory M1 macrophages to the anti-inflammatory M2 phenotype coincided with the revascularization as well as the appearance of osteoblasts in the fracture area. This indicates that M2 macrophages are necessary for the restoration of vessels and that they also play an orchestrating role in osteoblastogenesis during bone healing. The presence of adaptive immune cells throughout the healing process emphasizes their essential role for regenerative processes that exceeds a mere pathogen defense. B and T cells co-localize consistently with bone cells throughout the healing process, consolidating their crucial role in guiding bone formation. These histological data provide, for the first time, comprehensive information about the complex interrelationships of the cellular network during the entire bone healing process in one standardized set up. With this, an overall picture of the spatio-temporal interplay of cellular key players in a bone healing scenario has been created.

CONCLUSIONS

A spatio-temporal distribution of immune cells, bone cells, and factors driving bone healing at time points that are decisive for this process-especially during the initial steps of inflammation and revascularization, as well as the soft and hard callus phases-has been visualized. The results show that the bone healing cascade does not consist of five distinct, consecutive phases but is a rather complex interrelated and continuous process of events, especially at the onset of healing.

Progress of linking gut microbiota and musculoskeletal health: casualty, mechanisms, and translational values

The musculoskeletal system is important for balancing metabolic activity and maintaining health. Recent studies have shown that distortions in homeostasis of the intestinal microbiota are correlated with or may even contribute to abnormalities in musculoskeletal system function. Research has also shown that the intestinal flora and its secondary metabolites can impact the musculoskeletal system by regulating various phenomena, such as inflammation and immune and metabolic activities. Most of the existing literature supports that reasonable nutritional intervention helps to improve and maintain the homeostasis of intestinal microbiota, and may have a positive impact on musculoskeletal health. The purpose of organizing, summarizing and discussing the existing literature is to explore whether the intervention methods, including nutritional supplement and moderate exercise, can affect the muscle and bone health by regulating the microecology of the intestinal flora. More in-depth efficacy verification experiments will be helpful for clinical applications.

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.

Acetylsalicylic Acid Promotes Osteogenic Differentiation of Human Dental Pulp Mesenchymal Stem Cells and Regeneration of Alveolar Bone in Experimental Periodontitis Rats

Background

Periodontitis is characterized by bone resorption and periodontal tissue destruction owing to oral microbiota, mechanical stress, and systemic diseases such as diabetes mellitus. Human dental pulp mesenchymal stem cells (hDPMSCs) were analyzed as potential candidates for periodontal tissue regeneration. Acetylsalicylic acid (ASA), also known as aspirin, has been shown to promote osteogenic differentiation of mesenchymal stem cells. We investigated the effect of ASA pretreatment on periodontitis in order to achieve a more appealing prognosis of bone resorption.

Methods

The effect of ASA on cell proliferation was detected by the CCK-8 assay, and alkaline phosphatase (ALP) staining, alizarin red staining (ARS), and western blot were used to investigate the effect of different ASA concentrations on hDPMSCs' osteogenic differentiation and possible signaling pathways. Periodontitis was induced for 4 weeks. Stem cells pretreated with 50 µg/mL of ASA were transplanted into six-week-old male Sprague-Dawley rats by local and systemic injection once a week for two weeks. Four weeks after cell therapy, the rats were sacrificed for sampling to complete the molecular and morphological experiments.

Results

In vitro experiments revealed that 50 µg/mL of ASA had a significant effect on cell osteogenic differentiation. That is, when ASA was administered, the MAPK signaling pathway was activated. Notably, further vivo experiments revealed that ASA-hDPMSCs increased the area of bone regeneration and the OPG/RANKL ratio, suppressed TNF-α and IL-1 expression, and promote alveolar bone repair.

Conclusion

Our study extends the findings of previous research, firstly demonstrating that the use of ASA-pretreated hDPMSCs offers a novel therapy for the treatment of periodontitis for future clinical application.

Effect of pilose antler polypeptide on the mechanism of bone homeostasis in osteoporosis

Osteoporosis stands out as a prevalent metabolic disorder, bearing significant repercussions on human well-being and overall quality of life. It remains an urgent concern within the global public health framework due to its widespread occurrence. Osteoporosis arises from an abnormal metabolism in osteoblasts and osteoclasts, resulting in a disruption of the delicate equilibrium between bone formation and bone resorption. Within this context, deer antler peptides emerge as natural active compounds, wielding a pivotal role in governing the differentiation, proliferation, and mineralization of osteoblasts, as well as influencing the activity of osteoclasts. This article aims to consolidate our comprehension of the mechanisms underpinning the dynamic balance between bone formation and resorption, meticulously orchestrated by osteoblasts and osteoclasts in osteoporosis. Furthermore, it offers a comprehensive overview of how deer antler peptides, through their modulation of relevant signaling pathways, contribute to the enhancement of bone homeostasis. These insights deepen our understanding of the pathological processes through which deer antler peptides ameliorate bone homeostasis, while also presenting novel strategies for osteoporosis management.

Distinct defects in early innate and late adaptive immune responses typify impaired fracture healing in diet-induced obesity

Bone fractures, the most common musculoskeletal injuries, heal through three main phases: inflammatory, repair, and remodeling. Around 10% of fracture patients suffer from impaired healing that requires surgical intervention, a huge burden on the healthcare system. The rate of impaired healing increases with metabolic diseases such as obesity-associated hyperglycemia/type 2 diabetes (T2D), an increasing concern given the growing incidence of obesity/T2D. Immune cells play pivotal roles in fracture healing, and obesity/T2D is associated with defective immune-cell functions. However, there is a gap in knowledge regarding the stoichiometry of immune cells that populate the callus and how that population changes during different phases of healing. Here, we used complementary global and single-cell techniques to characterize the repertoire of immune cells in the fracture callus and to identify populations specifically enriched in the fracture callus relative to the unfractured bone or bone marrow. Our analyses identified two clear waves of immune-cell infiltration into the callus: the first wave occurs during the early inflammatory phase of fracture healing, while the second takes place during the late repair/early remodeling phase, which is consistent with previous publications. Comprehensive analysis of each wave revealed that innate immune cells were activated during the early inflammatory phase, but in later phases they returned to homeostatic numbers and activation levels. Of the innate immune cells, distinct subsets of activated dendritic cells were particularly enriched in the inflammatory healing hematoma. In contrast to innate cells, lymphocytes, including B and T cells, were enriched and activated in the callus primarily during the late repair phase. The Diet-Induced Obesity (DIO) mouse, an established model of obesity-associated hyperglycemia and insulin resistance, suffers from multiple healing defects. Our data demonstrate that DIO mice exhibit dysregulated innate immune responses during the inflammatory phase, and defects in all lymphocyte compartments during the late repair phase. Taken together, our data characterize, for the first time, immune populations that are enriched/activated in the callus during two distinct phases of fracture healing and identify defects in the healing-associated immune response in DIO mice, which will facilitate future development of immunomodulatory therapeutics for impaired fracture healing.

Effect of JAK inhibitors on the three forms of bone damage in autoimmune arthritis: joint erosion, periarticular osteopenia, and systemic bone loss

BACKGROUND

The types of bone damage in rheumatoid arthritis (RA) include joint erosion, periarticular osteoporosis, and systemic osteoporosis. Janus kinase (JAK) inhibitors ameliorate inflammation and joint erosion in RA, but their effect on the three types of bone loss have not been reportedly explored in depth. We aimed to clarify how JAK inhibitors influence the various types of bone loss in arthritis by modulating osteoclastic bone resorption and/or osteoblastic bone formation.

METHODS

Collagen-induced arthritis (CIA) mice were treated with a JAK inhibitor after the onset of arthritis. Micro-computed tomography (μCT) and histological analyses (bone morphometric analyses) on the erosive calcaneocuboid joint, periarticular bone (distal femur or proximal tibia), and vertebrae were performed. The effect of four different JAK inhibitors on osteoclastogenesis under various conditions was examined in vitro.

RESULTS

The JAK inhibitor ameliorated joint erosion, periarticular osteopenia and systemic bone loss. It reduced the osteoclast number in all the three types of bone damage. The JAK inhibitor enhanced osteoblastic bone formation in the calcaneus distal to inflammatory synovium in the calcaneocuboid joints, periarticular region of the tibia and vertebrae, but not the inflamed calcaneocuboid joint. All the JAK inhibitors suppressed osteoclastogenesis in vitro to a similar extent in the presence of osteoblastic cells. Most of the JAK inhibitors abrogated the suppressive effect of Th1 cells on osteoclastogenesis by inhibiting IFN-γ signaling in osteoclast precursor cells, while a JAK inhibitor did not affect this effect due to less ability to inhibit IFN-γ signaling.

CONCLUSIONS

The JAK inhibitor suppressed joint erosion mainly by inhibiting osteoclastogenesis, while it ameliorated periarticular osteopenia and systemic bone loss by both inhibiting osteoclastogenesis and promoting osteoblastogenesis. These results indicate that the effect of JAK inhibitors on osteoclastogenesis and osteoblastogenesis depends on the bone damage type and the affected bone area. In vitro studies suggest that while JAK inhibitors inhibit osteoclastic bone resorption, their effects on osteoclastogenesis in inflammatory environments vary depending on the cytokine milieu, JAK selectivity and cytokine signaling specificity. The findings reported here should contribute to the strategic use of antirheumatic drugs against structural damages in RA.

Role of denosumab in bone erosions in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by systemic inflammation and synovitis which evolve into joint destruction and deformity. Bone abnormalities are represented by marginal bone erosions and iuxta-articular and generalized osteoporosis. Overactivation of osteoclasts along with dysregulation of osteoblasts are the key events. Bone resorption is mediated by the receptor activator of nuclear factor (NF)-κB (RANK) ligand (RANK-L), responsible for the differentiation, proliferation, and activation of osteoclasts. RANK-L binds its receptor RANK, localized on the surface of preosteoclasts and mature osteoclasts promoting osteoclastogenesis. High levels of RANK-L were demonstrated in active RA patients. Denosumab, a fully human monoclonal antibody, binds RANK-L and suppresses the RANK-RANK-L signaling pathway leading to the inhibition of osteoclastogenesis. A retrospective analysis of published studies such as clinical trials evidenced the efficacy of denosumab in preventing bone erosion progression in RA patients. Key messages Key questions to answer in future include the following: Could denosumab be associated with other biologic therapies in RA patients? Could denosumab block the progression of bone damage in RA? Could denosumab be used for the prevention of bone erosion in RA?

Mechanistic insight of interleukin-9 induced osteoclastogenesis

Interleukin (IL)-9 is an emerging player in the pathogenesis of various chronic inflammatory diseases including bone disorders like rheumatoid arthritis (RA) and psoriatic arthritis. Recently, IL-9 was shown to enhance the osteoclast formation and their function in RA. However, the mechanisms by which IL-9 influences osteoclastogenesis are not known. Therefore, in this study we aimed to unravel the direct and indirect ways by which IL-9 can influence osteoclast formation. We used mouse bone marrow precursor cells for checking the effect of IL-9 on osteoclast differentiation and its function. Next, IL-9 induced signalling pathway were checked in the process of osteoclastogenesis. T cells play an important role in enhancing osteoclastogenesis in inflammatory conditions. We used splenic T cells to understand the impact of IL-9 on the functions of T effector (Teff) and regulatory T (Treg) cells. Furthermore, the effect of IL-9 mediated modulation of the T cell response on osteoclasts was checked using a coculture model of T cells with osteoclast precursors. We showed that IL-9 enhanced osteoclast formation and its function. We found that IL-9 activates STAT3, P38 MAPK, ERK1/2, NFκB and we hypothesize that it mediates the effect on osteoclastogenesis by accelerating mitochondrial biogenesis. Additionally, IL-9 was observed to facilitate the functions of pro-osteoclastogenic IL-17 producing T cells, but inhibits the function of anti-osteoclastogenic Treg cells. Our observations suggest that IL-9 can influence osteoclastogenesis directly by modulating the signalling cascade in the precursor cells; indirectly by enhancing IL-17 producing T cells and by reducing the functions of Treg cells.

Identification of 12 hub genes associated to the pathogenesis of osteoporosis based on microarray and single-cell RNA sequencing data

Osteoporosis is a common disease, especially among the elderly. This study aimed to comprehensively examine the roles of immune microenvironment in osteoporosis pathogenesis. Expression profiles of GSE35959, GSE7158, and GSE13850 datasets were used to analyze differential expression and identify hub genes related to immune features. Based on the single-cell RNA sequencing (scRNA-seq) data of an osteoporosis patient, different cell types were classified and the relation between immune environment and osteoporosis was explored. Twelve hub genes significantly associated with immune features were selected and 11 subgroups were defined using scRNA-seq data. The expression of two hub genes (CDKN1A and TEFM) was greatly altered during the transformation from mesenchymal stem cells (MSCs) to osteoblasts. Chemokines and chemokine receptors were differentially enriched in different cell types. CXCL12 was high-expressed in MSCs. This study emphasized that immune microenvironment played a critical role in the pathogenesis of osteoporosis. Chemokines and chemokine receptors can modify cell development and affect the interactions among different cell types, leading to unbalanced bone remodeling.

Exploring the shared gene signatures of smoking-related osteoporosis and chronic obstructive pulmonary disease using machine learning algorithms

Objectives: Cigarette smoking has been recognized as a predisposing factor for both osteoporosis (OP) and chronic obstructive pulmonary disease (COPD). This study aimed to investigate the shared gene signatures affected by cigarette smoking in OP and COPD through gene expression profiling. Materials and methods: Microarray datasets (GSE11784, GSE13850, GSE10006, and GSE103174) were obtained from Gene Expression Omnibus (GEO) and analyzed for differentially expressed genes (DEGs) and weighted gene co-expression network analysis (WGCNA). Least absolute shrinkage and selection operator (LASSO) regression method and a random forest (RF) machine learning algorithm were used to identify candidate biomarkers. The diagnostic value of the method was assessed using logistic regression and receiver operating characteristic (ROC) curve analysis. Finally, immune cell infiltration was analyzed to identify dysregulated immune cells in cigarette smoking-induced COPD. Results: In the smoking-related OP and COPD datasets, 2858 and 280 DEGs were identified, respectively. WGCNA revealed 982 genes strongly correlated with smoking-related OP, of which 32 overlapped with the hub genes of COPD. Gene Ontology (GO) enrichment analysis showed that the overlapping genes were enriched in the immune system category. Using LASSO regression and RF machine learning, six candidate genes were identified, and a logistic regression model was constructed, which had high diagnostic values for both the training set and external validation datasets. The area under the curves (AUCs) were 0.83 and 0.99, respectively. Immune cell infiltration analysis revealed dysregulation in several immune cells, and six immune-associated genes were identified for smoking-related OP and COPD, namely, mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1), tissue-type plasminogen activator (PLAT), sodium channel 1 subunit alpha (SCNN1A), sine oculis homeobox 3 (SIX3), sperm-associated antigen 9 (SPAG9), and vacuolar protein sorting 35 (VPS35). Conclusion: The findings suggest that immune cell infiltration profiles play a significant role in the shared pathogenesis of smoking-related OP and COPD. The results could provide valuable insights for developing novel therapeutic strategies for managing these disorders, as well as shedding light on their pathogenesis.

Recent advances of osteoimmunology research in rheumatoid arthritis: From single-cell omics approach

ABSTRACT

Cellular immune responses as well as generalized and periarticular bone loss are the key pathogenic features of rheumatoid arthritis (RA). Under the pathological conditions of RA, dysregulated inflammation and immune processes tightly interact with skeletal system, resulting in pathological bone damage via inhibition of bone formation or induction of bone resorption. Single-cell omics technologies are revolutionary tools in the field of modern biological research.They enable the display of the state and function of cells in various environments from a single-cell resolution, thus making it conducive to identify the dysregulated molecular mechanisms of bone destruction in RA as well as the discovery of potential therapeutic targets and biomarkers. Here, we summarize the latest findings of single-cell omics technologies in osteoimmunology research in RA. These results suggest that single-cell omics have made significant contributions to transcriptomics and dynamics of specific cells involved in bone remodeling, providing a new direction for our understanding of cellular heterogeneity in the study of osteoimmunology in RA.

RANKL and RANK in Cancer Therapy

Receptor activator of nuclear factor-κB (RANK) and its ligand (RANKL) are key regulators of mammalian physiology such as bone metabolism, immune tolerance and antitumor immunity, and mammary gland biology. Here, we explore the multiple functions of RANKL/RANK in physiology and pathophysiology and discuss underlying principles and strategies to modulate the RANKL/RANK pathway as a therapeutic target in immune-mediated cancer treatment.