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Purpose: To evaluate the feasibility of reversing a primary failure through therapeutic mechanical stimulation induced by transcutaneous application of acoustic waves (extracorporeal shockwave therapy [ESWT]) in the peri-implant tissues. Materials and Methods: This clinical report evaluates the outcome of a new protocol proposed to treat a primary failure (loosened oral implant): application of three cycles of ESWT (one session per week for 3 consecutive weeks) with an equivalent positive energy of 0.18 mJ/mm²(therapeutic dose: 2,000 pulses, 8 Hz, 4.0 bar). Standardized intraoral radiographs and CBCT scans were taken, the implant stability quotient (ISQ) was determined, and clinical evaluations were performed. Results: It was possible to verify a progressive increase in ISQ values after the ESWT protocol: 17 initially, 46 at 2 months, and 68 at 4 months. This led to successful implant prosthetic rehabilitation (35 Ncm). Follow-up evaluations at 6 years confirm that the new bone-implant interface is preserved and that ESWT is a safe, noninvasive treatment. Conclusions: In the context of the new dynamic model of osseointegration (the foreign body equilibrium), this represents the first report of a host-implant equilibrium reestablished after an early implant failure process. However, more studies are needed to determine both the medical device and the most effective therapeutic range for clinical applications of this technology in oral implantology. [ABSTRACT FROM AUTHOR]

AbstractObjectiveMethodsResultsConclusionOsteoimmunology is an emerging field that explores the interplay between bone and the immune system. The immune system plays a critical role in the pathogenesis of diabetes and significantly affects bone homeostasis. Artesunate, a first-line treatment for malaria, is known for its low toxicity and multifunctional properties. Increasing evidence suggests that artesunate possesses anti-inflammatory, immunoregulatory, and osteogenic effects. This review aims to explore the relationship between immune regulation and bone metabolism in type 2 diabetes (T2DM) and to investigate the potential therapeutic application of artesunate.This review systematically examines literature from PubMed/Medline, Elsevier, Web of Science, Embase, the International Diabetes Federation, and other relevant databases.This review synthesizes evidence from multiple sources to delineate the relationship between T lymphocytes and T2DM, the regulation of T lymphocyte subsets in bone metabolism, and the effects of artesunate on both T lymphocytes and bone metabolism. Recent studies suggest a bidirectional regulatory relationship between T2DM and T lymphocytes (CD4+ T and CD8+ T) during the onset and progression of the disease, with inflammatory and anti-inflammatory cytokines serving as key mediators. T lymphocyte subsets and their cytokines play a pivotal role in regulating osteogenesis and osteoclastogenesis in pathological conditions. Furthermore, artesunate has shown promise in modulating inflammatory infiltration and bone metabolism.The accumulated evidence indicates that artesunate exerts regulatory effects on bone metabolism in T2DM by influencing T lymphocyte differentiation. [ABSTRACT FROM AUTHOR]

Objective To assess the causal relationship between inflammatory factors and osteoporosis (OP), Methods GWAS data for 41 inflammatory factors and bone mineral density (BMD) were obtained from the GWAS catalog database and OP GWAS data were obtained from the Finnish database. Mendelian randomization analysis was conducted using inverse variance weighted method. (IVW), MR-Egger regression (MER), weighted median method (WME), simple median method and weighted mode method. IVW was primarily employed for analysis. Sensitivity analysis was performed to assess the reliability of result. The impact of single nucleotide polymorphisms on the outcome was evaluated using sleave-one-out analysis. Finally, drug prediction and molecular docking were conducted to further validate the pharmacological value of inflammatory factors. Results The study indicated a causal relationship between inflammatory factors and OP and BMD. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and monocyte chemoattractant protein-1 (MCP-1/MCAF) were positively associated with the risk of developing OP. Tumor necrosis factor β (TNF-B) was negatively associated with BMD in individuals aged 0-15. Interleukin-7 (IL-7) was negatively associated with BMD in individuals aged 15-30. Hepatocyte growth factor (HGF) was negatively associated with BMD in individuals aged 30-45. Macrophage inflammatory protein la (MIP-1a) and macrophage colony-stimulating factor (M-CSF) were negatively associated with BMD in individuals aged over 60. MIP-la was negatively associated with BMD across all age groups. Additionally, molecular docking confirmed the favorable binding between the drugs and proteins, further validating the pharmacological value of these targets. Conclusion The MR approach comprehensively evaluates the causal effects of 41 inflammatory factors on OP and BMD, indicating a causal association between inflammatory factors and OP and BMD. This suggests that intervention in inflammatory factors in the early stages of the disease could influence the development and progression of OP. [ABSTRACT FROM AUTHOR]

Patients with radiographic axial spondyloarthritis (r-axSpA) experience a higher prevalence of fragility fractures, though the pathophysiology of osteoporosis associated with this disease remains poorly understood. The objective of this study was to evaluate the histomorphometric data in r-axSpA patients. Male r-axSpA patients up to 55 years old were enrolled in this cross-sectional study. Clinical, lab, and imaging data, including spine X-Ray to evaluate vertebral fractures and new bone formation, as well as dual-energy X-ray absorptiometry (DXA) at spine, hip, and forearm and trabecular bone score (TBS), were performed in all patients. Transiliac histomorphometry was also underwent in all patients, and data were compared with 21 male cadavers’ material. A total of 21 patients were included, with a mean age of 45.8 years, long disease duration (median 17.5 years), mostly white (66.7%) and positive for HLA-B27 (90.5%). The prevalence of DXA abnormalities and low TBS (≤ 1.338) was 42.8% and 57.1%, respectively. There was higher osteoid trabecular thickness (p = 0.027) and cortical bone changes, including reduced thickness (p = 0.031) and increased porosity (p = 0.015) in r-axSpA patients. In addition, a pattern of cortical trabecularization was observed in 52.3%. Dynamic evaluation revealed a longer mineralization lag time (p = 0.0074) and lower mineralized surface (p = 0.0029) and bone formation rate (p = 0.0074) in patients compared to reference values. Our results showed a pattern of low trabecular remodeling, bone mineralization impairment, as well as cortical thickness and porosity abnormalities in men with r-axSpA. These findings may impact future treatment of bone fragility in this disease. [ABSTRACT FROM AUTHOR]

BACKGROUND: The incidence of osteoporosis significantly increases in the patients with rheumatoid arthritis, and it remains unclear whether the presence of a large number of immune complexes in serum promotes the onset and development of osteoporosis. OBJECTIVE: To investigate the correlation between serum immune complexes and osteoporosis in patients with rheumatoid arthritis. METHODS: (1) Clinical trial: Serum and clinical data of 50 healthy controls and 50 patients with untreated rheumatoid arthritis were collected and retrospectively analyzed. Total immune complex level in serum was compared between two groups. Correlation of serum total immune complexes with bone mineral density, bone turnover markers and other clinical indicators in patients with rheumatoid arthritis was analyzed. (2) Cell experiment: Peripheral blood mononuclear cells from healthy volunteers were isolated and cultured, and divided into four groups: rheumatoid arthritis group was added with total immune complex suspension from rheumatoid arthritis patients; normal control group was added with total immune complex suspension from healthy medical checkups; positive control group was added with α-MEM medium containing macrophage colony-stimulating factor and receptor activator of nuclear factorkappa B ligand, and negative control group was added with α-MEM medium. Tartrate-resistant acid phosphatase staining was performed to observe the formation of osteoclasts after 7 days of treatment, RESULTS AND CONCLUSION: (1) Clinical trial: The total immune complex and serum alkaline phosphatase levels in patients with rheumatoid arthritis were significantly higher than those in health controls (P < 0.01, P < 0.05). Pearson correlation analysis showed that serum total immune complex level was positively correlated with erythrocyte sedimentation rate (r=0.330, P=0.019), serum alkaline phosphatase (r=0.545, P=0.001), anti-cyclic citrullinate peptide (r=0.377, P=0.007) and c-terminal telopeptide of type I collagen (r=0.738, P=0.001), and negatively correlated with lumbar bone mineral density (r=-0.595, P=0.001) in patients with rheumatoid arthritis. Binary Logistic regression analysis showed that age [odds ratio (OR)=1.086, 95% confidence interval (CI) (1.022,1.154), P=0.008], anti-cyclic citrullinate peptide [OR=1.002, 95% CI (0.999,1.005), P=0.035], c-terminal telopeptide of type I collagen [OR=0.141, 95% CI (0.015, 8.900), P=0.008] and serum total immune complexes [OR=2.895, 95% CI (1.228, 6.827), P=0.001] were the influencing factors for abnormal bone mass (reduced bone mass or osteoporosis) in patients with rheumatoid arthritis. (2) Cell experiment: Tartrate-resistant acid phosphatase positive osteoclasts were observed in the positive control group, normal control group and rheumatoid arthritis group, and there were more osteoclasts in the rheumatoid arthritis group than in the normal control group (P < 0.01). To conclude, serum total immune complexes can be used as a potential serologic predictor of rheumatoid arthritis complicated with osteoporosis, and removing immune complexes in serum or interfering with the binding of immune complexes to their receptors may be an effective means for the prevention and treatment of rheumatoid arthritis complicated with osteoporosis. [ABSTRACT FROM AUTHOR]

Macrophage efferocytosis (clearance of apoptotic cells) is crucial for tissue homeostasis and wound repair, where macrophages secrete factors that promote resolution of inflammation and regenerative signalling. This study examined the role of efferocytic macrophage‐associated CCL2 secretion, its influence on mesenchymal stem/progenitor cell (MSPC) chemotaxis, and in vivo cell recruitment using Ccr2−/− (KO) mice with disrupted CCL2 receptor signalling in two regenerative models: ossicle implants and ulnar stress fractures. Single cell RNA sequencing and PCR validation indicated that efferocytosis of various apoptotic cells at bone injury sites (osteoblasts, pre‐osteoblasts, MSPC) upregulated CCL2. CCL2 gradients enhanced MSPC migration through type I collagen matrices. In vivo, MSPC (LepR+) infiltration was significantly reduced while macrophage (F4/80+) infiltration increased in KO ossicle implants versus WT. In ulnar stress fractures, micro‐CT revealed increased mineralized callus incidence in CCR2 KO male mice 5 days post injury (dpi) versus WT. By 7‐dpi callus fractional bone volume, trabecular thickness, and bone mineral density were increased versus WT. Immunohistochemistry of mice 5‐dpi confirmed an increase in callus area (including soft tissue); however, the percent of osteoprogenitors (%Osx+) within the callus was not different. These findings suggest that CCL2 differentially impacts MSPC recruitment depending on bone wound healing model. [ABSTRACT FROM AUTHOR]

Bone metastases are a prevalent complication in advanced cancers, particularly in breast, prostate, and lung cancers, and are associated with severe skeletal-related events (SREs), including fractures, spinal cord compression, and debilitating pain. Conventional bone-targeted treatments like bisphosphonates and RANKL inhibitors (denosumab) reduce osteoclast-mediated bone resorption but do not directly impact tumor progression within the bone. This review focuses on examining the growing potential of immunotherapy in targeting the unique challenges posed by bone metastases. Even though immune checkpoint inhibitors (ICIs) have significantly changed cancer treatment, their impact on bone metastases appears limited because of the bone microenvironment's immunosuppressive traits, which include high levels of transforming growth factor-beta (TGFβ) and the immune-suppressing cells, such as regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs). This review underscores the investigation of combined therapeutic approaches that might ease these difficulties, such as the synergy of immune checkpoint inhibitors with agents aimed at bones (denosumab, bisphosphonates), chemotherapy, and radiotherapy, as well as the combination of immune checkpoint inhibitors with different immunotherapeutic methods, including CAR T-cell therapy. This review provides a comprehensive analysis of preclinical studies and clinical trials that show the synergistic potential of these combination approaches, which aim to both enhance immune responses and mitigate bone destruction. By offering an in-depth exploration of how these strategies can be tailored to the bone microenvironment, this review underscores the need for personalized treatment approaches. The findings emphasize the urgent need for further research into overcoming immune evasion in bone metastases, with the goal of improving patient survival and quality of life. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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.

Bingpeng Lin,1,2,&ast; Yufei Fan,2,&ast; Xuechao Yang,2 Janak L Pathak,2 Mei Zhong3 1Department of Orthodontics, School and Hospital of Stomatology, Guangzhou Medical University, Guangzhou, 510180, People’s Republic of China; 2Guangdong Engineering Research Center of Oral Restoration and Reconstruction, Guangzhou Key Laboratory of Basic and Applied Research of Oral Regenerative Medicine, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, 510182, People’s Republic of China; 3Department of Prosthodontics, School and Hospital of Stomatology, Guangzhou Medical University, Guangzhou, 510180, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Janak L Pathak; Mei Zhong, Email J.pathak@gzhmu.edu.cn; 2016686043@gzhmu.edu.cnAbstract: Periodontal disease is a common disorder affecting a wide range of people and has a high prevalence globally. Periodontitis comprises a series of inflammatory conditions affecting periodontal support tissue, which could ultimately lead to tooth loss and reduce life quality and add to the financial burden of society. Matrix metalloproteinase-12 (MMP-12) is an elastase that is produced mostly by macrophages and could degrade a wide spectrum of extracellular matrix (ECM) and also contribute to several systematic pathological conditions. Recently, researchers have reported higher expression of MMP-12 in chronic periodontitis patients. However, there are few reports on the role of MMP-12 in periodontitis pathogenicity, and the interaction between MMP-12, periodontal pathogens, and periodontal tissues remains unclear. In this review, we introduce the potentially unique role of MMP-12 in the context of periodontal inflammation earlier, summarize the possible effects of MMP-12 on the pathological process of periodontitis and the interaction of host response under the challenge of various inflammatory factors, and provide possible diagnostic and therapeutic strategies targeting MMP-12 for the management of periodontitis. Future research and policies should focus on and implement effective chairside testing methods to reduce the prevalence of periodontal diseases.Keywords: matrix metalloproteinase-12, periodontitis, dysbiosis, epithelial barrier, immunity, osteoimmunology

Heterotopic ossification (HO), often arising in response to traumatic challenges, results from the aberrant osteochondral differentiation of mesenchymal stem cells (MSCs). Nevertheless, the impact of trauma‐induced inflammatory exposure on MSC fate determination remains ambiguous. In this study, the cellular diversity within inflammatory lesions is elucidated, comprising MSCs and several innate and adaptive immune cells. It is observed that quiescent MSCs transition into cycling MSCs, subsequently giving rise to chondrogenic (cMSC) and/or osteogenic (oMSC) lineages within the inflammatory microenvironment following muscle or tendon injuries, as revealed through single‐cell RNA sequencing (scRNA‐seq), spatial transcriptome and lineage tracing analysis. Moreover, these investigations demonstrate that neutrophils and natural killer (NK) cells enhance transition of quiescent MSCs into cycling MSCs, which is also controlled by M1 macrophages, a subpopulation of macrophages can also stimulate cMSC and oMSC production from cycling MSCs. Additionally, M2 macrophages, CD4+ and CD8+ T lymphocytes are found to promote chondrogenesis. Further analysis demonstrates that immune cells promotes the activation of signaling transducers and activators of transcription (STAT) pathway and phosphoinositide 3 (PI3K)/protein kinase B (AKT) pathway in MSC proliferation and osteochondral progenitors' production, respectively. These findings highlight the dynamics of MSC fate within the inflammatory lesion and unveil the molecular landscape of osteoimmunological interactions, which holds promise for advancing HO treatment. [ABSTRACT FROM AUTHOR]

Osteoporosis is a progressive metabolic bone disease characterized by decreased bone density and microarchitectural deterioration, leading to an increased risk of fracture, particularly in postmenopausal women and the elderly. Increasing evidence suggests that inflammatory processes play a key role in the pathogenesis of osteoporosis and are strongly associated with the activation of osteoclasts, the cells responsible for bone resorption. In the present study, we investigated, for the first time, the influence of proinflammatory cytokines on the osteogenic differentiation, proliferation, and metabolic activity of primary human osteoblast-like cells (OBs) derived from the femoral heads of elderly patients. We found that all the proinflammatory cytokines, IL-1β, TNF-α, IL-6, and IL-8, enhanced the extracellular matrix mineralization of OBs under differentiation-induced cell culture conditions. In the cases of IL-1β and TNF-α, increased mineralization was correlated with increased osteoblast proliferation. Additionally, IL-1β- and TNF-α-increased osteogenesis was accompanied by a rise in energy metabolism due to improved glycolysis or mitochondrial respiration. In conclusion, we show here, for the first time, that, in contrast to findings obtained with cell lines, mesenchymal stem cells, or animal models, human OBs obtained from patients exhibited significantly enhanced osteogenesis upon exposure to proinflammatory cytokines, probably in part via a mechanism involving enhanced cellular energy metabolism. This study significantly contributes to the field of osteoimmunology by examining a clinically relevant cell model that can help to develop treatments for inflammation-related metabolic bone diseases. [ABSTRACT FROM AUTHOR]

Bone defects arising from trauma and tumors present a potential risk of infection and compromise host immune function. Within a dysfunctional microenvironment, the uncontrolled breeding of bacteria and persistent chronic inflammation exacerbate bone loss, impeding bone regeneration and repair. Macrophages function as specialized phagocytes within the immune microenvironment and the orchestrated role of distinct phenotypes during regeneration has attracted significant attention. The M1 phenotype exhibits antimicrobial activities to eliminate bacterial threats, while the M2 phenotype secretes anti‐inflammatory mediators to fine‐tune the immune microenvironment. Here, a biphasic delivery system consisting of a photothermal agent (graphene oxide, GO) coated and an immune modulator (urolithin A, UA) encapsulated in coaxial electrospun nanofibers with a dynamic regulation function of macrophage behavior is designed. It is observed that the GO coating exhibited remarkable photothermal performance within the near‐infrared window, affecting the phagocytic activity of macrophage subsets in an integrin‐RhoA‐ROCK1 dependent manner. The sustained release of UA from the core layer induced a phenotypic switch by downregulating TNF signaling and upregulating TGF signaling. This system also demonstrated a promotion of bone regeneration in vivo. Overall, this strategy achieved sequential regulation of macrophage phenotypes, effectively preventing infection and fostering bone tissue regeneration. [ABSTRACT FROM AUTHOR]

Macrophages and osteocytes are important regulators of inflammation, osteogenesis and osteoclastogenesis. However, their interactions under adverse conditions, such as biomaterial-associated infection (BAI) are not fully understood. We aimed to elucidate how factors released from macrophages modulate osteocyte responses in an in vitro indirect 3D co-culture model. Human monocyte-derived macrophages were cultured on etched titanium disks and activated with either IL-4 cytokine (anti-inflammatory M2 phenotype) or Staphylococcus aureus secreted virulence factors to simulate BAI (pro-inflammatory M1 phenotype). Primary osteocytes in collagen gels were then stimulated with conditioned media (CM) from these macrophages. The osteocyte response was analyzed by gene expression, protein secretion, and immunostaining. M1 phenotype macrophages were confirmed by IL-1β and TNF-α secretion, and M2 macrophages by ARG-1 and MRC-1. Osteocytes receiving M1 CM revealed bone inhibitory effects, denoted by reduced secretion of bone formation osteocalcin (BGLAP) and increased secretion of the bone inhibitory sclerostin (SOST). These osteocytes also downregulated the pro-mineralization gene PHEX and upregulated the anti-mineralization gene MEPE. Additionally, exhibited pro-osteoclastic potential by upregulating pro-osteoclastic gene RANKL expression. Nonetheless, M1-stimulated osteocytes expressed a higher level of the potent pro-osteogenic factor BMP-2 in parallel with the downregulation of the bone inhibitor genes DKK1 and SOST , suggesting a compensatory feedback mechanisms. Conversely, M2-stimulated osteocytes mainly upregulated anti-osteoclastic gene OPG expression, suggesting an anti-catabolic effect. Altogether, our findings demonstrate a strong communication between M1 macrophages and osteocytes under M1 (BAI)-simulated conditions, suggesting that the BAI adverse effects on osteoblastic and osteoclastic processes in vitro are partly mediated via this communication. Biomaterial-associated infections are major challenges and the underlying mechanisms in the cellular interactions are missing, especially among the major cells from the inflammatory side (macrophages as the key cell in bacterial clearance) and the regenerative side (osteocyte as main regulator of bone). We evaluated the effect of macrophage polarization driven by the stimulation with bacterial virulence factors on the osteocyte function using an indirect co-culture model, hence mimicking the scenario of a biomaterial-associated infection. The results suggest that at least part of the adverse effects of biomaterial associated infection on osteoblastic and osteoclastic processes in vitro are mediated via macrophage-to-osteocyte communication. [Display omitted] [ABSTRACT FROM AUTHOR]

Background: Bone regeneration is a well‐regulated dynamic process, of which the prominent role of the immune system on bone homeostasis is more and more revealed by recent research. Before fully activation of the bone remodeling cells, the immune system needs to clean up the microenvironment in facilitating the bone repair initiation. Furthermore, this microenvironment must be maintained properly by various mechanisms over the entire bone regeneration process. Objective: This review aims to summarize the role of the T‐helper 17/Regulatory T cell (Th17/Treg) balance in bone cell remodeling and discuss the relevant progress in bone tissue engineering. Results: The role of the immune response in the early stages of bone regeneration is crucial, especially the impact of the Th17/Treg balance on osteoclasts, mesenchymal stem cells (MSCs), and osteoblasts activity. By virtue of these knowledge advancements, innovative approaches in bone tissue engineering, such as nano‐structures, hydrogel, and exosomes, are designed to influence the Th17/Treg balance and thereby augment bone repair and regeneration. Conclusion: Targeting the Th17/Treg balance is a promising innovative strategy for developing new treatments to enhance bone regeneration, thus offering potential breakthroughs in bone injury clinics. [ABSTRACT FROM AUTHOR]

The aim of this study was to identify single-nucleotide polymorphisms (SNPs) in bone remodeling-related genes associated with disease severity and bone mineral density (BMD) in early arthritis (EA) patients. For this purpose, the genotyping of 552 SNPs located in gene regions of semaphorins 4b, 4d, 4f, DKK1, 2 and 3, sclerostin, OPG, RANK and RANKL was performed using Immunochip from Illumina Inc. in 268 patients from the Princesa Early Arthritis Register Longitudinal (PEARL) study. Measurements of BMD and disease activity were chosen as outcome variables to select SNPs of interest. The relationships of SNPs with the BMD of the forearm, lumbar spine and hip (Hologic-4500 QDR) were analyzed by linear regression adjusted for age, sex, body mass index and presence of anti-citrullinated peptide antibodies (ACPAs). The association of each SNP with activity variables was analyzed by linear regression, logistic regression or ordered logistic regression according to the variable, and multivariate models were adjusted for potentially confounding variables, such as age, sex and presence of ACPAs. These analyses showed that four SNPs located in the genes coding for RANK (TNFRSF11A) and OPG (TNFRSF11B) were significantly associated with clinical variables of severity. SNP rs1805034 located in exon 6 of TNFRSF11A, which causes a non-synonymous (A/V) mutation, showed significant association with BMD and therefore may be considered as a possible biomarker of severity in RA patients. SNPs in the OPG gene showed an association with serum OPG levels and predicted disease activity after two years of follow-up. [ABSTRACT FROM AUTHOR]

The immune system plays an important role in fracture healing, by modulating the pro-inflammatory and anti-inflammatory responses occurring instantly upon injury. An imbalance in these responses can lead to adverse outcomes, such as non-union of fractures. Implants are used to support and stabilize complex fractures. Biodegradable metallic implants offer the potential to avoid a second surgery for implant removal, unlike non-degradable implants. However, considering our dynamic immune system it is important to conduct in-depth studies on the immune response to these implants in living systems. In this study, we investigated the immune response to Mg and Mg-10Gd in vivo in a rat femur fracture model with external fixation. In vivo imaging using liposomal formulations was used to monitor the fluorescence-related inflammation over time. We combine ex vivo methods with our in vivo study to evaluate and understand the systemic and local effects of the implants on the immune response. We observed no significant local or systemic effects in the Mg-10Gd implanted group compared to the SHAM and Mg implanted groups over time. Our findings suggest that Mg-10Gd is a more compatible implant material than Mg, with no adverse effects observed in the early phase of fracture healing during our 4-week study. Degradable metallic implants in form of Mg and Mg-10Gd intramedullary pins were assessed in a rat femur fracture model, alongside a non-implanted SHAM group with special respect to the potential to induce an inflammatory response. This pre-clinical study combines innovative non-invasive in vivo imaging techniques associated with multimodal, ex vivo cellular and molecular analytics. The study contributes to the development and evaluation of degradable biometals and their clinical application potential. The study results indicate that Mg-10Gd did not exhibit any significant harmful effects compared to the SHAM and Mg groups. [Display omitted] [ABSTRACT FROM AUTHOR]

Johann Lechner,1 Volker von Baehr,2 Florian Notter,1 Fabian Schick1 1Clinic for Integrative Dentistry, Munich, Germany; 2Department of Immunology and Allergology, Institute for Medical Diagnostics, Berlin, GermanyCorrespondence: Johann Lechner, Gruenwalder Str. 10A, Munich, 81547, Germany, Tel +49 89 697 0129, Fax +49 89 692 5830, Email drlechner@aol.comIntroduction: Osteoimmunology recognizes the relationship between bone cells and immune cells. Chronic osteoimmune dysregulation is present in bone marrow defects of the jaw (BMDJ) as fatty-degenerative osteonecrosis (FDOJ). In comparison to samples from healthy jaw bone, the cytokine analysis of samples of BMDJ/FDOJ from 128 patients showed downregulated TNF-α and IL-6 expression and the singular overexpression of the chemokine RANTES/CCL5.Aim and Objectives: This paper raises the question of whether the osteoimmune defects due to incomplete wound healing in BMDJ/FDOJ in 128 patients are related to dysregulation of the Th1/Th2 ratio and regulatory T cell (T-reg) expression in a control group of 197 BMDJ/FDOJ patients, each presenting with BMDJ/FJOD and one of seven different immune disorders.Material and Methods: In the control group, serum concentrations of the cytokines IFN-y and IL-4 were determined after stimulated cytokine release and displayed as Th1/Th2 ratios.Results: Data show a shift in Th2 in more than 80% (n = 167) of the control cohort of 197 chronically ill patients with concomitant BMDJ/FDOJ. In these 167 subjects, the Th1/Th2 ratio was < 6.1 demonstrating impaired immune regulation. Forty-seven subjects or 30% showed not only a shift in Th2 but also excessive T-reg overactivation with levels of > 1.900 pg/mL, indicating strongly downregulated immune activity.Discussion: BMDJ/FDOJ is characterized by a lack of Th1 cytokines and an excessive expression of RANTES/CCL5 and IL-1ra and, thus, the inversion of an acute inflammatory cytokine pattern. In contrast, abdominal fat contains a very high proportion of regulatory Th1 cells and produces an inflammatory immune response through the high overexpression of TNF-α and IL-6. The lack of Th1 activation in BMDJ/FDOJ areas inhibits normal wound healing and supports the persistence of BMDJ/FDOJ.Conclusion: The Th1/Th2 ratio requires greater consideration, especially with respect to wound healing following dental surgical interventions, such as jaw surgery, implantation and augmentation, to avoid the emergence of the osteoimmune situation that is characteristic of BMDJ/FDOJ. Keywords: osteoimmunology, T-cells, Th1/Th2 shift, jawbone, osteoclastogenesis, RANTES/CCL5

Bone- and cartilage-related diseases, such as osteoporosis and osteoarthritis, affect millions of people worldwide, impairing their quality of life and increasing mortality. Osteoporosis significantly increases the bone fracture risk of the spine, hip, and wrist. For successful fracture treatment and to facilitate proper healing in the most complicated cases, one of the most promising methods is to deliver a therapeutic protein to accelerate bone regeneration. Similarly, in the setting of osteoarthritis, where degraded cartilage does not regenerate, therapeutic proteins hold great promise to promote new cartilage formation. For both osteoporosis and osteoarthritis treatments, targeted delivery of therapeutic growth factors, with the aid of hydrogels, to bone and cartilage is a key to advance the field of regenerative medicine. In this review article, we propose five important aspects of therapeutic growth factor delivery for bone and cartilage regeneration: (1) protection of protein growth factors from physical and enzymatic degradation, (2) targeted growth factor delivery, (3) controlling GF release kinetics, (4) long-term stability of regenerated tissues, and (5) osteoimmunomodulatory effects of therapeutic growth factors and carriers/scaffolds.

Ankylosing spondylitis (AS) is a chronic inflammatory autoimmune disease characterized by inflammatory back pain. Its pathological features mainly include inflammation, bone destruction, and pathologic new bone formation. The etiology of AS is complex, and it may be related to genetics, infections, the environment, and intestinal flora. Its pathogenesis has not yet been clarified. In recent years, osteoimmunology, as a new theme in the study of inflammatory arthritis, plays an important role in the pathogenesis and development of AS, which was embodied in the inflammatory response and imbalance of bone metabolism. Traditional Chinese medicine (TCM) has the characteristics of multiple pathways, multiple components, multiple targets and multiple levels. TCM can improve the inflammatory response and bone metabolism imbalance of AS by regulating the osteoblasts of the skeletal system and the related factors of the immune system, thus to prevent and control AS. For this reason, the paper summarizes the role of bone immunology in the pathogenesis of AS, and reviews the current status of research on the intervention of TCM in bone immunology for the treatment of AS, with a view to providing certain references for the future clinical application of TCM in the prevention and treatment of AS. [ABSTRACT FROM AUTHOR]

With the aging of the social population increasingly serious, the number of patients with osteoporosis is gradually increasing, and it has become a serious public health problem. Postmenopausal osteoporosis (PMOP) is one of the primary osteoporosis. Due to the lack of estrogen in postmenopausal women, it accelerates bone loss, mainly manifested as pain and susceptibility to fractures, which brings great inconvenience to daily life. Bone immunology focuses on the link between the skeletal system and the immune system. Activated lymphocytes release various cytokines to participate in the process of bone remodeling. Traditional Chinese medicine is widely used in clinic and has obvious effect on PMOP treatment. Based on bone immunology, this paper introduced the effect of traditional Chinese medicine on bone metabolism and discussed the mechanism of traditional Chinese medicine in treating PMOP. [ABSTRACT FROM AUTHOR]

Purpose of the Review: In this review, we discuss the most recent scientific advances on the reciprocal regulatory interactions between the skeletal and hematopoietic stem cell niche, focusing on immunomodulation and its interplay with the cell's mitochondrial function, and how this impacts osteoimmune health during aging and disease. Recent Findings: Osteoimmunology investigates interactions between cells that make up the skeletal stem cell niche and immune system. Much work has investigated the complexity of the bone marrow microenvironment with respect to the skeletal and hematopoietic stem cells that regulate skeletal formation and immune health respectively. It has now become clear that these cellular components cooperate to maintain homeostasis and that dysfunction in their interaction can lead to aging and disease. Summary: Having a deeper, mechanistic appreciation for osteoimmune regulation will lead to better research perspective and therapeutics with the potential to improve the aging process, skeletal and hematologic regeneration, and disease targeting. [ABSTRACT FROM AUTHOR]

Bone functions not only as a critical element of the musculoskeletal system but also serves as the primary lymphoid organ harboring hematopoietic stem cells (HSCs) and immune progenitor cells. The interdisciplinary field of osteoimmunology has illuminated the dynamic interactions between the skeletal and immune systems, vital for the maintenance of skeletal tissue homeostasis and the pathogenesis of immune and skeletal diseases. Aberrant immune activation stimulates bone cells such as osteoclasts and osteoblasts, disturbing the bone remodeling and leading to skeletal disorders as seen in autoimmune diseases like rheumatoid arthritis. On the other hand, intricate multicellular network within the bone marrow creates a specialized microenvironment essential for the maintenance and differentiation of HSCs and the progeny. Dysregulation of immune–bone crosstalk in the bone marrow environment can trigger tumorigenesis and exacerbated inflammation. A comprehensive deciphering of the complex "immune–bone crosstalk" leads to a deeper understanding of the pathogenesis of immune diseases as well as skeletal diseases, and might provide insight into potential therapeutic approaches. [ABSTRACT FROM AUTHOR]

Objective Based on the influence of the immune system on bone metabolism, this paper analyzed the feasibility of improving bone metabolism through kidney regulation of the immune system to prevent and control Osteoporosis from the theory of "kidney stores essence", with the aim of providing more ideas for in-depth research and prevention of Osteoporosis. Methods The connection between the immune system and bone metabolism was explored by searching the literature on CNKI and Pubmed databases about the immune system and bone metabolism, and the connection between the kidneys and the immune system was explored by reading the traditional Chinese medical literature on the theory of "kidney stores essence". ResultsImmune cells originate from bone marrow, and immune cells and immune cytokines can affect bone metabolism. The kidney, due to its function as "storing essence", is closely related to the immune system through its role as the "house of yin and yang", masteing bone and transforming into the blood, and transforming into the marrow up to the brain. Conclusion Based on the influence of the immune system on bone metabolism and the theory of "kidney stores essence", it is theoretically feasible to improve bone metabolism through kidney regulation of the immune system to prevent and treat Osteoporosis, which is worthy of further in-depth study. [ABSTRACT FROM AUTHOR]

Bone healing occurs through three consecutive and interdependent phases. While the acute inflammatory response is vital to fracture healing, chronic and systemic inflammation negatively affect the healing process. The bone tissue relies heavily on the immune system for its normal physiology and turnover. The interactions are more pronounced in injury states, such as fractures and autoimmune disorders. Recently, the field of osteoimmunology, the study of the molecular interplay of the immune and skeletal systems, has gained much-needed attention to develop new therapeutic strategies to accelerate fracture healing and prevent the complications of fracture healing. This review provides an overview of the process of fracture healing and discusses the role of immune cells, their interplay with the released cytokines, and the current state of the art in the field of osteoimmunology. [ABSTRACT FROM AUTHOR]

Abstract Rare earth nanomaterials (RE NMs), which are based on rare earth elements, have emerged as remarkable biomaterials for use in bone regeneration. The effects of RE NMs on osteogenesis, such as promoting the osteogenic differentiation of mesenchymal stem cells, have been investigated. However, the contributions of the properties of RE NMs to bone regeneration and their interactions with various cell types during osteogenesis have not been reviewed. Here, we review the crucial roles of the physicochemical and biological properties of RE NMs and focus on their osteogenic mechanisms. RE NMs directly promote the proliferation, adhesion, migration, and osteogenic differentiation of mesenchymal stem cells. They also increase collagen secretion and mineralization to accelerate osteogenesis. Furthermore, RE NMs inhibit osteoclast formation and regulate the immune environment by modulating macrophages and promote angiogenesis by inducing hypoxia in endothelial cells. These effects create a microenvironment that is conducive to bone formation. This review will help researchers overcome current limitations to take full advantage of the osteogenic benefits of RE NMs and will suggest a potential approach for further osteogenesis research. Graphical abstract

Abstract A wealth of evidence intimates a profound connection between the immune system and osteonecrosis, albeit the specific immune factors underlying this connection remain largely veiled. A bidirectional Mendelian randomization (MR) study was conducted based on genome-wide association study summary data to identify causal links between 731 immune factors and osteonecrosis including drug-induced osteonecrosis. Preliminary MR analysis was accomplished utilizing the inverse-variance weighted method under a multiplicative random effects model, and heterogeneity and potential horizontal pleiotropy were evaluated through Cochrane's Q-test, MR-Egger intercept test, MR-PRESSO global test, and leave-one-out analysis. Upon false discovery rate correction, the gene-predicted level of one immune factor (CD62L − monocyte %monocyte) exhibited a significant positive correlation with osteonecrosis, while eight immune traits associated with monocytes, dendritic cells, and NK cells demonstrated significant causal effects with drug-induced osteonecrosis. Reverse MR revealed no significant correlations. This MR research provides genetic evidence for the causal associations between a broad spectrum of immune factors and osteonecrosis. Such a study aids in unraveling the intricate interaction patterns between the immune and skeletal systems, elucidating the pathogenesis of osteonecrosis, and identifying potential novel therapeutic approaches.

BACKGROUND: Osteoporosis is a disease in which bone density and structure are destroyed and fractures are caused by increased bone fragility, leading to high clinical disability and mortality rates. OBJECTIVE: To review the research progress in the role of bone immunity in physiological and pathological processes related to bone metabolism, providing ideas for the research and clinical application of bone immunity in bone diseases. METHODS: The first author searched PubMed and CNKI databases in November 2022 for relevant literature using the keywords of “osteoimmunology, immuno-skeletal interface, bone metabolism, skeletal metabolism, lymphocyte, immune factor” in English and Chinese, respectively. The time range of retrieval was mainly from January 2010 to November 2022, and a small number of classical long-term literatures were included. After reading the topic and abstract for preliminary screening and excluding repetitive studies, low-quality journals and unrelated literature, 81 documents were finally included for review. RESULTS AND CONCLUSION: Osteoimmunology refers to that bone and immune cells share the same microenvironment and interact with each other to jointly perform the “bone immune system,” which includes all cells in the bone marrow. Immuno-skeletal interface has protective effects on bone under physiological conditions, but it may lead to bone destruction under pathological conditions. Osteoprotegerin is mainly derived from B cells and can inhibit osteoclast metabolism. However, when the body is in an inflammatory state, T cells and B cells work together to promote bone resorption. In addition, interleukin-1, interleukin-6 and tumor necrosis factor-α regulate the expression of receptor activator of nuclear factor-κB ligand in vivo and affect bone metabolism. In most clinical diseases (such as rheumatoid arthritis, estrogen deficiency, HIV infection, and hyperparathyroidism), the immuno-skeletal interface interacts with the bone immune system, resulting in the regulation of bone metabolism. In terms of clinical prospect, the interaction between bone immunity and bone metabolism should be studied in order to propose new strategies for therapeutic intervention to reduce the risk of fracture. [ABSTRACT FROM AUTHOR]

Postmenopausal osteoporosis (PMOP) is a common bone metabolic disease characterized by decreased bone mass, destruction of bone structure, and an increased risk of fracture. PMOP has become an unfavorable factor that threatens women's health and economic development. Studies on the mechanism associated with estrogen deficiency-induced PMOP have progressed in recent years, but remain insufficiently elucidated. Osteoimmunologic studies have shown that the pathological process of PMOP is accompanied by inflammation and involvement of the immune system. Macrophages, an important component of immune system cells, have been reported to play a role in bone homeostasis and regeneration. Macrophage depletion exacerbates bone loss in OVX mice, and significantly reduces the number of BMSCs and their osteogenic differentiation capacity. The effect of macrophage deletion on bone formation appears to outweigh its effect on osteoclast activity, and crosstalk between MΦ and BMSCs may play an important role in this process. This paper reviews the correlation between the crosstalk of MΦ-BMSCs and postmenopausal osteoporosis based on the theory of osteoimmunology, aiming to provide new ideas for research on the prevention and treatment of PMOP. [ABSTRACT FROM AUTHOR]

Macrophages are key regulators in bone repair and regeneration. Recent studies have shown that long-term epigenetic changes and metabolic shifts occur during specific immune training of macrophages that affect their functional state, resulting in heightened (trained) or reduced (tolerant) responses upon exposure to a second stimulus. This is known as innate immune memory. Here, we study the impact of macrophages' memory trait on osteoblast differentiation of human mesenchymal stromal cells (hMSCs) and osteoclast differentiation. An in vitro trained immunity protocol of monocyte-derived macrophages was employed using inactivated Candida albicans and Bacillus Calmette–Guérin (BCG) to induce a 'trained' state and Pam3CSK4 (PAM) and Lipopolysaccharides (LPS) to induce a 'tolerance' state. Macrophages were subsequently cocultured with hMSCs undergoing osteogenic differentiation during either resting (unstimulated) or inflammatory conditions (restimulated with LPS). Alkaline phosphatase activity, mineralization, and cytokine levels (TNF, IL-6, oncostatin M and SDF-1α) were measured. In addition, macrophages underwent osteoclast differentiation. Our findings show that trained and tolerized macrophages induced opposing results. Under resting conditions, BCG-trained macrophages enhanced ALP levels (threefold), while under inflammatory conditions this was found in the LPS-tolerized macrophages (fourfold). Coculture of hMSCs with trained macrophages showed mineralization while tolerized macrophages inhibited the process under both resting and inflammatory conditions. While osteoclast differentiation was not affected in trained-macrophages, this ability was significantly loss in tolerized ones. This study further confirms the intricate cross talk between immune cells and bone cells, highlighting the need to consider this interaction in the development of personalized approaches for bone regenerative medicine. [ABSTRACT FROM AUTHOR]

Bone remodeling is an essential, delicately balanced physiological process of coordinated activity of bone cells that remove and deposit new bone tissue in the adult skeleton. Due to the complex nature of this process, many mathematical models of bone remodeling have been developed. Each of these models has unique features, but they have underlying patterns. In this review, the authors highlight the important aspects frequently found in mathematical models for bone remodeling and discuss how and why these aspects are included when considering the physiology of the bone basic multicellular unit, which is the term used for the collection of cells responsible for bone remodeling. The review also emphasizes the view of bone remodeling from a systems biology perspective. Understanding the systemic mechanisms involved in remodeling will help provide information on bone pathology associated with aging, endocrine disorders, cancers, and inflammatory conditions and enhance systems pharmacology. Furthermore, some features of the bone remodeling cycle and interactions with other organ systems that have not yet been modeled mathematically are discussed as promising future directions in the field. [ABSTRACT FROM AUTHOR]

A wealth of evidence intimates a profound connection between the immune system and osteonecrosis, albeit the specific immune factors underlying this connection remain largely veiled. A bidirectional Mendelian randomization (MR) study was conducted based on genome-wide association study summary data to identify causal links between 731 immune factors and osteonecrosis including drug-induced osteonecrosis. Preliminary MR analysis was accomplished utilizing the inverse-variance weighted method under a multiplicative random effects model, and heterogeneity and potential horizontal pleiotropy were evaluated through Cochrane's Q-test, MR-Egger intercept test, MR-PRESSO global test, and leave-one-out analysis. Upon false discovery rate correction, the gene-predicted level of one immune factor (CD62L − monocyte %monocyte) exhibited a significant positive correlation with osteonecrosis, while eight immune traits associated with monocytes, dendritic cells, and NK cells demonstrated significant causal effects with drug-induced osteonecrosis. Reverse MR revealed no significant correlations. This MR research provides genetic evidence for the causal associations between a broad spectrum of immune factors and osteonecrosis. Such a study aids in unraveling the intricate interaction patterns between the immune and skeletal systems, elucidating the pathogenesis of osteonecrosis, and identifying potential novel therapeutic approaches. [ABSTRACT FROM AUTHOR]

Rare earth nanomaterials (RE NMs), which are based on rare earth elements, have emerged as remarkable biomaterials for use in bone regeneration. The effects of RE NMs on osteogenesis, such as promoting the osteogenic differentiation of mesenchymal stem cells, have been investigated. However, the contributions of the properties of RE NMs to bone regeneration and their interactions with various cell types during osteogenesis have not been reviewed. Here, we review the crucial roles of the physicochemical and biological properties of RE NMs and focus on their osteogenic mechanisms. RE NMs directly promote the proliferation, adhesion, migration, and osteogenic differentiation of mesenchymal stem cells. They also increase collagen secretion and mineralization to accelerate osteogenesis. Furthermore, RE NMs inhibit osteoclast formation and regulate the immune environment by modulating macrophages and promote angiogenesis by inducing hypoxia in endothelial cells. These effects create a microenvironment that is conducive to bone formation. This review will help researchers overcome current limitations to take full advantage of the osteogenic benefits of RE NMs and will suggest a potential approach for further osteogenesis research. [ABSTRACT FROM AUTHOR]

Biological aging profoundly impairs the homeostasis of the skeletal system. Cellular senescence, a hallmark of biological aging, plays an instrumental role in bone disease. The underlying mechanisms of cellular senescence, triggered by both intracellular and extracellular stimuli, are multifaceted and yet to be uncovered. Recent research indicates that acute cellular senescence often serves beneficial roles, such as contributing to growth, development, and tissue regeneration. By contrast, chronic cellular senescence, primarily driven by the accumulation of senescent cells (SnCs) and the release of senescence-associated secretory phenotypes (SASP), has detrimental effects on the skeletal system by irreversibly disrupting bone homeostasis and promoting age-related disorders. Furthermore, the bone marrow is rich in immune cells and their exposure to SASP often leads to immune dysfunction, resulting in unresolved chronic inflammation and compromised adaptive immunity. Until now, the impact of SnCs and SASP on the skeleton has remained elusive. Meanwhile, extensive efforts are being made to combat age-related diseases through various strategies. Among them, SnCs and SASP are the primary targets for antiaging therapeutic clearance, resulting in the development of "senolytics" and "senomorphics," respectively. In this review, we summarize and highlight the role of SnCs and SASP in skeletal pathophysiology, the mechanism of cellular senescence in affecting bone metabolism, and potential therapeutic approaches, particularly senolytics and senomorphics, in treating cellular senescence-related bone diseases. [ABSTRACT FROM AUTHOR]

Bone fracture repair is a complex, multi-step process that involves communication between immune and stromal cells to coordinate the repair and regeneration of damaged tissue. In the US, 10% of all bone fractures do not heal properly without intervention, resulting in non-union. Complications from non-union fractures are physically and financially debilitating. We now appreciate the important role that immune cells play in tissue repair, and the necessity of the inflammatory response in initiating healing after skeletal trauma. The temporal dynamics of immune and stromal cell populations have been well characterized across the stages of fracture healing. Recent studies have begun to untangle the intricate mechanisms driving the immune response during normal or atypical, delayed healing. Various in vivo models of fracture healing, including genetic knockouts, as well as in vitro models of the fracture callus, have been implemented to enable experimental manipulation of the heterogeneous cellular environment. The goals of this review are to (1): summarize our current understanding of immune cell involvement in fracture healing (2); describe state- of-the art approaches to study inflammatory cells in fracture healing, including computational and in vitro models; and (3) identify gaps in our knowledge concerning immune-stromal crosstalk during bone healing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Innate lymphoid cells (ILCs) are the most recently identified immune cell types existing in lymphoid and nonlymphoid organs. Albeit they lack the expression of antigen receptors, ILCs play vital roles in innate immune responses by producing multiple effector cytokines. The ILC family includes conventional natural killer cells and cytokine‐producing ILCs, which are divided into group 1, group 2, and group 3 ILCs based on their effector cytokines and developmental requirements. Emerging evidence has indicated that ILCs are essential immune regulators of bone homeostasis, playing a critical role in osteoimmunology. In this mini‐review, we discuss recent advances in the understanding of ILC functions in bone homeostasis under physiological and pathological conditions, with an emphasis on the communication between ILCs and bone cells including osteoclasts and osteoblasts, as well as the underlying immunoregulatory networks involving ILC‐derived cytokines and growth factors. This review also discusses future research directions and the potential of targeting ILCs for the treatment of inflammation‐associated bone disorders. [ABSTRACT FROM AUTHOR]

The contributions of skeletal cells to the processes of B cell development in the bone marrow (BM) have not been completely described. The von-Hippel Lindau protein (VHL) plays a key role in cellular responses to hypoxia. Previous work showed that Dmp1-Cre;Vhl conditional knockout mice (VhlcKO), which deletes Vhl in subsets of mesenchymal stem cells, late osteoblasts and osteocytes, display dysregulated bone growth and reduction in B cells. Here, we investigated the mechanisms underlying the B cell defects using flow cytometry and high-resolution imaging. In the VhlcKO BM, B cell progenitors were increased in frequency and number, whereas Hardy Fractions B-F were decreased. VhlcKO Fractions B-C cells showed increased apoptosis and quiescence. Reciprocal BM chimeras confirmed a B cell-extrinsic source of the VhlcKO B cell defects. In support of this, VhlcKO BM supernatant contained reduced CXCL12 and elevated EPO levels. Intravital and ex vivo imaging revealed VhlcKO BM blood vessels with increased diameter, volume, and a diminished blood-BM barrier. Staining of VhlcKO B cells with an intracellular hypoxic marker indicated the natural existence of distinct B cell microenvironments that differ in local oxygen tensions and that the B cell developmental defects in VhlcKO BM are not initiated by hypoxia. Our studies identify novel mechanisms linking altered bone homeostasis with drastic BM microenvironmental changes that dysregulate B cell development.

Yi-Ming Gao,1 Yan Pei,1 Fei-Fei Zhao,2 Ling Wang1 1Department of Orthopedic Oncology, The Third Hospital of Hebei Medical University, Shijiazhuang, Hebei, People’s Republic of China; 2Department of Orthopedics, The Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei, People’s Republic of ChinaCorrespondence: Ling Wang, Tel +86031188603682, Email wangling2016uw@126.comAbstract: Osteosarcoma is an extremely malignant tumor, and its pathogenesis is complex and remains incompletely understood. Most cases of osteosarcoma are accompanied by symptoms of bone loss or result in pathological fractures due to weakened bones. Enhancing the survival rate of osteosarcoma patients has proven to be a long-standing challenge. Numerous studies mentioned in this paper, including in-vitro, in-vivo, and in-situ studies have consistently indicated a close association between the symptoms of bone loss associated with osteosarcoma and the presence of osteoclasts. As the sole cells capable of bone resorption, osteoclasts participate in a malignant cycle within the osteosarcoma microenvironment. These cells interact with osteoblasts and osteosarcoma cells, secreting various factors that further influence these cells, disrupting bone homeostasis, and shifting the balance toward bone resorption, thereby promoting the onset and progression of osteosarcoma. Moreover, the interaction between osteoclasts and various other cells types, such as tumor-associated macrophages, myeloid-derived suppressor cells, DCs cells, T cells, and tumor-associated fibroblasts in the osteosarcoma microenvironment plays a crucial role in disease progression. Consequently, understanding the role of osteoclasts in osteosarcoma has sparked significant interest. This review primarily examines the physiological characteristics and functional mechanisms of osteoclasts in osteosarcoma, and briefly discusses potential therapies targeting osteoclasts for osteosarcoma treatment. These studies provide fresh ideas and directions for future research on the treatment of osteosarcoma.Keywords: osteosarcoma, osteoclasts, bone remodeling, osteoimmunology, bone microenvironment

The recognition and importance of immune cells during bone regeneration, including around bone biomaterials, has led to the development of an entire field termed "osteoimmunology," which focuses on the connection and interplay between the skeletal system and immune cells. Most studies have focused on the "osteogenic" capacity of various types of bone biomaterials, and much less focus has been placed on immune cells despite being the first cell type in contact with implantable devices. Thus, the amount of literature generated to date on this topic makes it challenging to extract needed information. This review article serves as a guide highlighting advancements made in the field of osteoimmunology emphasizing the role of the osteoimmunomodulatory properties of biomaterials and their impact on osteoinduction. First, the various immune cell types involved in bone biomaterial integration are discussed, including the prominent role of osteal macrophages (OsteoMacs) during bone regeneration. Thereafter, key biomaterial properties, including topography, wettability, surface charge, and adsorption of cytokines, growth factors, ions, and other bioactive molecules, are discussed in terms of their impact on immune responses. These findings highlight and recognize the importance of the immune system and osteoimmunology, leading to a shift in the traditional models used to understand and evaluate biomaterials for bone regeneration. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Tristetraprolin (TTP; also known as NUP475, GOS24, or TIS11), encoded by Zfp36, is an RNA‐binding protein that regulates target gene expression by promoting mRNA decay and preventing translation. Although previous studies have indicated that TTP deficiency is associated with systemic inflammation and a catabolic‐like skeletal phenotype, the mechanistic underpinnings remain unclear. Here, using both TTP‐deficient (TTPKO) and myeloid‐specific TTPKO (cTTPKO) mice, we reveal that global absence or loss of TTP in the myeloid compartment results in a reduced bone microarchitecture, whereas gain‐of‐function TTP knock‐in (TTPKI) mice exhibit no significant loss of bone microarchitecture. Flow cytometry analysis revealed a significant immunosuppressive immune cell phenotype with increased monocytic myeloid‐derived suppressor cells (M‐MDSCs) in TTPKO and cTTPKO mice, whereas no significant changes were observed in TTPKI mice. Single‐cell transcriptomic analyses of bone marrow myeloid progenitor cell populations indicated a dramatic increase in early MDSC marker genes for both cTTPKO and TTPKO bone marrow populations. Consistent with these phenotypic and transcriptomic data, in vitro osteoclastogenesis analysis of bone marrow M‐MDSCs from cTTPKO and TTPKO displayed enhanced osteoclast differentiation and functional capacity. Focused transcriptomic analyses of differentiated M‐MDSCs showed increased osteoclast‐specific transcription factors and cell fusion gene expression. Finally, functional data showed that M‐MDSCs from TTP loss‐of‐function mice were capable of osteoclastogenesis and bone resorption in a context‐dependent manner. Collectively, these findings indicate that TTP plays a central role in regulating osteoclastogenesis through multiple mechanisms, including induction of M‐MDSCs that appear to regulate skeletal phenotype. [ABSTRACT FROM AUTHOR]