RANKL biology: bone metabolism, the immune system, and beyond

Effect of microgravity on bone Tissue: Mechanisms of osteodegeneration and advanced treatment modalities

Preeminent human existence in space raises concerns about bone health due to the effect of microgravity on bone tissue degeneration. Space experiments pose logistical challenges, but ground-based research using microgravity simulation provides information about bone loss mechanisms. This review compiles and evaluates data from astronaut, animal, and cellular experiments, emphasizing microgravity-induced skeletal deconditioning. These findings contribute to creating treatment approaches for preventing bone loss risks in space and potentially on Earth. Astronauts experience notable bone loss, up to 1 %-2 % per month in a gravity-less environment, predominantly influencing weight-bearing bones. These necessitate finding efficient treatment approaches for preventing bone loss risks in space and potentially on Earth. There is a significant need to investigate microgravity's impact on various bone compartments and skeletal recovery processes. The current review explores the stages of bone remodeling and the fundamental causes of bone loss in microgravity, including effects on osteoblasts, osteocytes, osteoclasts, hematopoietic stem cells, and bone marrow stromal cells, as well as the impact on calcium levels. The article also explores various treatment options, including general management, recent therapies, supportive therapies, and emerging therapies such as BP-NELL-PEG, melatonin, calcitonin, and molecular therapies, highlighting their therapeutic potential against microgravity-induced bone loss.

Pamidronate regulates the osteogenic differentiation of periosteal-derived mesenchymal stem cells in congenital tibial pseudarthrosis via OPG/RANKL

BACKGROUND

Congenital pseudarthrosis of the tibia (CPT) is one of the most challenging conditions in orthopedics. Previous research indicates a strong association between CPT and neurofibromatosis type 1 (NF1). The clinical application of pamidronate has demonstrated efficacy in enhancing bone healing and alleviating NF1-associated bone pathology in specific CPT cases. Nevertheless, the precise mechanistic basis for these therapeutic effects remains poorly characterized, warranting further investigation.

METHODS

In this study, mesenchymal stem cells (MSCs) were isolated from patients with congenital pseudarthrosis of the tibia (CPT MSCs) and from patients undergoing corrective osteotomy (control group). We examined cell conditions post-treatment with pamidronate disodium at concentrations of 0 nM, 10 nM, 100 nM, and 1 μM, evaluating proliferation, toxicity, and differentiation potential, while investigating its effects on the OPG/RANKL pathway. Additionally, we analyzed the alterations in mitogen-activated protein kinase signaling and its correlation with the regulatory expression of OPG/RANKL genes.

RESULTS

This study demonstrated that the proliferation and osteogenic differentiation of CPT MSCs were significantly lower than those of the control group. Treatment with pamidronate disodium enhanced both proliferation and osteogenic differentiation in CPT MSCs. Furthermore, pamidronate disodium treatment decreased RANKL expression and increased OPG protein levels in CPT MSCs, activating p38 and ERK1/2 signaling pathways. Notably, the co-administration of p38 or ERK1/2 inhibitors significantly diminished the proliferation and osteogenic differentiation of CPT MSCs treated with pamidronate disodium.

CONCLUSION

Pamiphosphonate disodium can promote the proliferation and osteogenic differentiation of CPT MSCs by activating p38 and ERK1/2 signaling.

Advancements in bone organoids: perspectives on construction methodologies and application strategies

BACKGROUND

In clinical practice and research, bone defects due to tumor growth, trauma, and different pathological conditions are significant challenges. Although bone possesses an intrinsic capacity for regeneration, extensive bone abnormalities necessitate applying advanced methods for regenerating bone. Bone organoids have made methodological breakthroughs in this field, and the use of bone organoids to repair bone defects has gained wide acceptance in the scientific community, supported by a large body of experimental evidence.

AIM OF REVIEW

This review synthesizes existing literature and ground-breaking studies to provide an in-depth examination of the bone organoid model, exploring the fundamental architecture and development of bone and emphasizing recent advancements in bone organoid fabrication, such as the application of 3D bioprinting technology in bone organoid fabrication. Furthermore, the study suggests potential directions for future research, highlighting the critical role of interdisciplinary collaboration in fully harnessing the potential of this rapidly evolving field. Key scientific concepts of review Bone organoids involve the 3D self-organization of in vitro-cultured bone-associated stem cells, optionally including extracellular matrix components. This process generates tissue closely resembling the original bone tissue's functional, genetic, and structural features. Bone organoids are more promising than traditional methods of bone defect repair. In addition, tissue engineering technologies such as 3D bioprinting have opened up new opportunities for constructing bone organoids. Future research should prioritize the development of composite bone organoids, enhancement of bone organoid stiffness, and improvement of bioactive materials, as well as the exploration and development of novel bioinks to facilitate the application of bone organoids in bone repair and regeneration.

Cytokines and oral cancer risk: Genetic evidence from a bidirectional Mendelian randomization study

This study aimed to elucidate the causal relationship between cytokines and oral cancer using Mendelian randomization (MR) analysis. Utilizing genetic data from genome-wide association studies (GWAS) and publicly available datasets, we conducted a bidirectional 2-sample MR analysis. The study design employed single nucleotide polymorphisms as genetic instruments to investigate the link between cytokines and oral cancer. The analysis was based on data from 2 cohorts with total 132 cytokines: 41 cytokines from comprehensive GWAS meta-analysis data, 91 cytokines from GWAS summary statistics for circulating inflammatory cytokines. Oral cancer genetic association data was sourced from the FinGen R10 datasets. To discern the causal relationship between cytokines and oral cancer, 5 MR methodologies, including inverse variance weighted and MR-Egger regression, weighted median, weighted mode, and simple mode were applied. The MR analysis revealed nominal associations between certain cytokines and the risk of oral cancer. Specifically, increased levels of C-X-C motif chemokine ligand 9 (odd ratios [OR] = 0.760, 0.600-0.962, 95% confidence interval [CI] 0.600-0.962, P = .023), monocyte chemoattractant protein 1 (OR = 0.78, 95% CI 0.32-0.99, P = .046), and TNF related activation induced cytokine (OR = 0.792, 95% CI 0.630-0.994, P = .044) were associated with a reduced risk of oral cancer, while higher levels of monocyte chemoattractant protein 2 (OR = 1.164, 95% CI 1.001-1.353, P = .048) and CC motif chemokine 25 (OR = 1.434, 95% CI 1.106-1.858, P = .006) were linked to an increased risk. The reverse analysis suggested a possible effect of oral cancer on the level of circulating cytokines, particularly Fractalkine (OR = 0.942, 95% CI 0.897-0.990, P = .019). No evidence of heterogeneity or significant pleiotropy was detected, validating the instrumental variables used. The findings support a causal relationship between specific cytokines and the risk of oral cancer, highlighting the complex interplay between inflammatory mediators and cancer development. These results underscore the importance of individualized immune profiling in treating oral cancer patients and pave the way for future research into targeted therapies based on cytokine profiles.

A six-month weight loss intervention is associated with significant changes in serum biomarkers related to inflammation, bone and cartilage metabolism in obese patients with psoriatic arthritis and matched controls

BACKGROUND

Obesity is highly overrepresented in patients with psoriatic arthritis (PsA) and associated with increased disease activity and inferior treatment outcome. We have previously reported in 41 patients with PsA and body mass index (BMI) ≥ 33 kg/m2 that weight loss treatment with Very Low Energy Diet (VLED) resulted in a median weight loss of 18,6% and concomitantly a significant improvement in C-reactive protein (CRP) and disease activity at six months (M6). This sub-study analyzes the effects on serum biomarkers associated with inflammation, bone and cartilage metabolism in the same PsA patients and matched controls.

METHODS

Patients and controls received VLED treatment (640 kcal/day) during 12-16 weeks depending on baseline (BL) BMI < 40 or ≥ 40 kg/m2, followed by an energy restricted diet. Serum was collected at BL and M6, and biomarkers were measured with Magnetic Luminex® Assays and enzyme-linked immunosorbent assay (ELISA). Nonparametric statistics and paired comparison tests were used.

RESULTS

In the PsA patients, the following proteins were significantly reduced at M6 as compared to BL: hepatocyte growth factor (HGF) (median (first-third quartile) 327.9 (250.3-413.6) pg/mL vs. 271.3 (206.9-331.0) pg/mL, p < 0.01), vascular endothelial growth factor (VEGF) (79.6 (55.9-113.5) pg/mL vs. 69.6 (53.1-105.3) pg/mL, p = 0.01), B-cell activating factor (BAFF) (794.4 (716.4-868.3) pg/mL vs. 674.6 (613.2-790.5) pg/mL, p = 0.01) and cartilage oligomeric matrix protein (COMP) (266.1 (209.9-366.0) ng/mL vs. 217.0 (156.0-272.0) ng/mL, p < 0.01), whereas carboxyterminal telopeptide of type-1 collagen (CTX-1) was significantly increased (268.0 (196.0-378.5) pg/mL vs. 508.0 (350.0-640.0) pg/mL, p < 0.01). Similar results were found in the control group.

CONCLUSIONS

Weight loss was associated with reduced levels of serum biomarkers related to inflammation and cartilage degradation, and increased biomarkers for bone resorption. The study supports the strong relationship between obesity, inflammation, bone and cartilage metabolism, identifying BMI as a possible confounder for biomarker levels.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02917434, registered on September 21, 2016, retrospectively registered.

Activating Transcription Factor 3 (ATF3) Regulates Cellular Senescence and Osteoclastogenesis via STAT3/ERK and p65/AP-1 Pathways in Human Periodontal Ligament Cells

Oral cellular aging plays a critical role in the pathogenesis of chronic periodontitis and alveolar bone resorption. Although activating transcription factor 3 (ATF3) has been implicated as a senescence-associated factor, its specific role in periodontal ligament cell (PDLC) senescence remains unclear. Human PDLCs were exposed to lipopolysaccharide (LPS, 1 μg/mL) and nicotine (5 mM) for 3 days to induce senescence. ATF3 expression was silenced using siRNA. The expression of senescence-associated secretory phenotype (SASP) factors (IFNγ, IL6, IL8, TNFα, and IL1β) and the secretion of nitric oxide (NO) and prostaglandin E2 (PGE2) were assessed by RT-PCR and immunoassay. Conditioned media (CM) from these cells were applied to mouse bone marrow macrophages (BMMs) to evaluate osteoclast differentiation and bone resorption. In addition, key signaling pathways, including STAT3, ERK, NF-κB (p65), and AP-1, were investigated by Western blotting and immunofluorescence. ATF3 knockdown markedly reduced the LPS/nicotine-induced expression of SASP factors and decreased NO and PGE2 levels. CM from ATF3-silenced PDLCs markedly inhibited osteoclast differentiation, as evidenced by reduced tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells and diminished bone resorption. Moreover, ATF3 inhibition led to a decreased RANKL/OPG ratio and attenuated the phosphorylation of STAT3 and ERK, along with the reduced nuclear translocation of p65 and AP-1 components. These findings suggest that ATF3 plays a critical role in mediating cellular senescence and osteoclastogenesis in PDLCs. Targeting ATF3 may represent a novel therapeutic strategy for managing age-related oral diseases, such as chronic periodontitis.

Therapeutic Advantages of Isoflavone Glycoside and Aglycone Forms of Sophoricoside in the Amelioration of Postmenopausal Symptoms: Bone Health, Metabolic Regulation, and Systemic Inflammation

This study investigates the therapeutic potential of sophoricoside and its aglycone metabolite, genistein, derived from Styphnolobium japonicum L. fruit, as natural alternatives to hormone replacement therapy for postmenopausal symptom management. Using Lactobacillus plantarum to model intestinal biotransformation, we compared glycoside-rich (Rex) and aglycone-rich (Rex-AG) extracts in ovariectomized rats. Both treatments significantly reduced weight gain and alleviated vaginal dryness, with Rex demonstrating superior thermoregulatory stabilization. Histological and molecular analyses revealed preserved trabecular bone integrity through the downregulation of RANKL and upregulation of TGF-β. Both extracts exhibited potent anti-inflammatory effects in adipose tissue, suppressing IL-6 and TNF-α, while regulating adipogenesis markers (FABP4, KLF, leptin, PPARγ) more effectively than 17β-estradiol. Serum genistein concentrations confirmed its efficient biotransformation and systemic bioavailability. Importantly, the treatments showed favorable safety profiles with no adverse effects on organ weight. These findings establish S. japonicum L. fruit-derived phytoestrogens as promising candidates for the comprehensive management of postmenopausal symptoms, offering an efficacious and safer alternative to conventional hormone therapy.

New Perspectives on Postmenopausal Osteoporosis: Mechanisms and Potential Therapeutic Strategies of Sirtuins and Oxidative Stress

Estrogen levels are the core factor influencing postmenopausal osteoporosis (PMOP). Estrogen can affect the progression of PMOP by regulating bone metabolism, influencing major signaling pathways related to bone metabolism, and modulating immune responses. When estrogen levels decline, the activity of Sirtuins (SIRTs) is reduced. SIRTs are enzymes that function as NAD+-dependent deacetylases. SIRTs can modulate osteocyte function, sustain mitochondrial homeostasis, and modulate relevant signaling pathways, thereby improving bone metabolic imbalances, reducing bone resorption, and promoting bone formation. In PMOP, SIRT1, SIRT3, and SIRT6 are primarily affected. Oxidative stress (OS) is a crucial factor in PMOP, as it generates excessive reactive oxygen species (ROS) that exacerbate PMOP. There is a certain interplay between SIRTs and OS. The reduced activity of SIRTs leads to intensified OS and the excessive accumulation of ROS. In return, ROS suppresses the AMPK signaling pathway and the synthesis of NAD+, which consequently diminishes the function of SIRTs. Natural SIRT activators and natural antioxidants, which are characterized by high safety, convenience, and minimal side effects, represent a potential therapeutic strategy for PMOP. This study aims to investigate the mechanisms of SIRTs and OS in PMOP and summarize potential therapeutic strategies to assist in the improvement of PMOP.

ILC3s promote intestinal tuft cell hyperplasia and anthelmintic immunity through RANK signaling

Helminth infections, particularly in developing countries, remain a notable health burden worldwide. Group 3 innate lymphoid cells (ILC3s) are enriched in the intestine and play a critical role in immunity against extracellular bacteria and fungi. However, whether ILC3s are involved in intestinal helminth infection is still unclear. Here, we report that helminth infection reprograms ILC3s, which, in turn, promote anthelmintic immunity. ILC3-derived RANKL [receptor activator of NF-κB (nuclear factor κB) ligand] synergizes with interleukin-13 (IL-13) to facilitate intestinal tuft cell expansion after helminth infection, which further activates the tuft cell-group 2 innate lymphoid cell (ILC2) circuit to control helminth infection. Deletion of RANKL in ILC3s or deletion of RANK or its downstream adaptor RelB in intestinal epithelial cells substantially diminishes tuft cell hyperplasia and dampens anthelmintic immunity. Thus, ILC3s play an indispensable role in protecting against helminth infection through the regulation of intestinal tuft cell hyperplasia and type 2 immunity.

Structures and biological activities of anti-osteoporotic drugs: An overview of promising small-molecule therapeutics for the treatment of osteoporosis

Osteoporosis is the most common metabolic skeletal disorder of the skeleton, stemming from a cellular imbalance between bone formation by osteoblasts and bone resorption by osteoclasts. This imbalance causes bones to become weak and brittle, thus increasing the risk of fractures. The prevalence of osteoporosis escalates with advancing age, thereby presenting a considerable public health challenge that has elicited substantial public concern. Existing anti-osteoporotic drugs typically act by inhibiting bone resorption, promoting bone formation, and exerting a dual effect. Yet, most of these pharmaceuticals have fundamental limitations, such as targeting only one specific site and a tendency to cause side effects. With advancements in anti-osteoporotic medications, numerous new small-molecule drugs have been developed and synthesized. These novel active compounds exhibit good anti-osteoporotic activity both in vitro and in vivo by enhancing osteoblast differentiation and mineralization, as well as inhibiting osteoclast resorption. The present study seeks to review the development and current status of new compounds exhibiting anti-osteoporotic activity, to establish a solid foundation for preventing and treating osteoporosis, promoting pharmacological research, and aiding in developing new medications.

The role of palmitoylation modifications in the regulation of bone cell function, bone homeostasis, and osteoporosis

Osteoporosis a is a metabolic bone disease caused by an imbalance in bone homeostasis, which is regulated by osteoblasts and osteoclasts. Protein palmitoylation modification is a post-translational modification that affects protein function, localization, and targeting by attaching palmitoyl groups to specific amino acid residues of proteins. Recent studies have shown that protein palmitoylation is involved in the regulation of osteoclast overproduction, osteoblast migration, osteogenic differentiation, dysfunctional autophagy, and endocrine hormone membrane receptors in osteoporosis. Exactly to what extent palmitoylation modifications can regulate osteoporosis, and whether palmitoylation inhibition can delay osteoporosis, is a key question that needs to be investigated urgently. In this review, we observed that palmitoylation modifications act mainly through two target cells - osteoblasts and osteoclasts - and that the targets of palmitoylation modifications are focused on plasma membrane proteins or cytosolic proteins of the target cells, which tend to assume the role of receiving extracellular signals. We also noted that different palmitoyl transferases acting on different substrate proteins exert conflicting regulation of osteoblast function. We concluded that the regulation of osteocyte function, bone homeostasis, and osteoporosis by palmitoylation modifications is multidimensional, diverse, and interconnected. Perfecting the palmitoylation modification network can enhance our ability to utilize post-translational modifications to resist osteoporosis and lay the foundation for targeting palmitoyl transferases to treat osteoporosis in the future.

Role of Masticatory Force in Modulating Jawbone Immunity and Bone Homeostasis: A Review

Mastication exerts a significant influence on both the structural and immunological environment of the jawbone. The mechanical stress generated during chewing initiates bone remodeling through the coordinated activities of osteoclasts and osteoblasts, with these processes being modulated by immune cell responses. This review summarizes the interaction between masticatory forces and jawbone immunity, focusing on key mechanisms such as mechanotransduction in osteocytes, macrophage polarization, and the activation of T cells. The review also delves into the role of the receptor activator of nuclear factor κ-B ligand (RANKL), receptor activator of nuclear factor κ-B (RANK), and osteoprotegerin (OPG) signaling pathway, highlighting its critical function in bone resorption and immune regulation. Additionally, the review summarizes how masticatory forces modulate the immune response through changes in immune cells, particularly focusing on cytokines, and the involvement of hormonal and molecular pathways. These findings provide valuable insights into the complex interplay between mechanical forces and immune cells, with implications for bone health.

Salidroside inhibits osteoclast differentiation based on osteoblast-osteoclast interaction via HIF-1a pathway

This study investigated the regulatory potential of salidroside (SAL), a primary active compound in Rhodiola rosea L., on osteoclast differentiation by modulating the hypoxia-inducible factor 1-alpha (HIF-1a) pathway in osteoblasts. Luciferase reporter assay and chromatin immunoprecipitation (ChIP) assay were employed to validate whether the receptor activator of nuclear factor-?B ligand (RANKL) is the downstream target gene of HIF-1a in osteoblasts. The study also utilized lipopolysaccharide (LPS)-induced mouse osteolysis to examine the impact of SAL on osteolysis in vivo. Furthermore, conditioned medium (CM) from SAL-pretreated osteoblasts was used to investigate the paracrine effects on osteoclastogenesis through the HIF-1a pathway. Hypoxic condition-induced overexpression of HIF-1a upregulated RANKL levels by binding to the RANKL promoter and enhancing transcription in osteoblastic cells. In vivo, SAL significantly alleviated bone tissue hypoxia and decreased the expression of HIF-1a by downregulating the expression of RANKL, vascular endothelial growth factor (VEGF), interleukin 6 (IL-6), and angiopoietin-like 4 (ANGPTL4). In the paracrine experiment, conditioned media from SAL-pretreated osteoblasts inhibited differentiation through the HIF-1a/RANKL, VEGF, IL-6, and ANGPTL4 pathways. RANKL emerges as the downstream target gene regulated by HIF-1a in osteoblasts. SAL significantly alleviates bone tissue hypoxia and bone loss in LPS-induced osteolysis through the HIF-1a/RANKL, VEGF, IL-6, and ANGPTL4 pathways. SAL inhibits osteoclast differentiation by regulating osteoblast paracrine secretion.

Osteoimmunology: Crosstalk Between T Cells and Osteoclasts in Osteoporosis

Osteoporosis, a common metabolic condition that affects the bones, increases the risk of fractures, thereby diminishing one's quality of life and, in severe cases, can even result in life-threatening conditions. Osteoporosis is becoming increasingly prevalent worldwide as the population ages. Previous research on osteoporosis has focused on skeletal cellular components such as osteoblasts and osteoclasts. The emerging field of "osteoimmunology" has recently been introduced through new research. The concept highlights the critical impact of bone-immune system interactions on osteoporosis progression. The pathogenesis of osteoporosis is significantly influenced by T cells, particularly cytotoxic and helper T cells, which modulate osteoclast differentiation and activity. A crucial aspect of understanding osteoporosis is how T lymphocytes interact with osteoclasts. However, the precise mechanisms underlying T cell-osteoclast crosstalk remain poorly understood. This review systematically examines T cell and osteoclast involvement in osteoimmunology, with a particular focus on their involvement in osteoporosis. It seeks to elucidate the immune mechanisms driving the progression of osteoporosis and identify key molecules involved in T cell-osteoclast interactions. This aims to discover novel molecular targets and intervention strategies to improve early diagnosis and management of osteoporosis. Furthermore, this article will explore the potential of intervening in T cell-osteoclast interactions using conventional therapies, traditional Chinese medicine, immunomodulatory agents, and nanomaterial-based treatments, providing new perspectives for future osteoporosis management.

Alterations of bone proteins in medication-related osteonecrosis of the jaw

Changes in the protein expression pattern of osteoblastic lineage cells from the alveolar bone (OLAB) during medication-related osteonecrosis of the jaw (MRONJ) have rarely been investigated. This lack of information is partly because of the limited availability of healthy samples and the lack of human alveolar bone cell lines for research. The aim of the present study was to investigate the bone proteins collagen 1, runt-related transcription factor 2 (RUNX2), and tumor necrosis factor ligand superfamily member 11 (RANKL). Furthermore, we established a cell lineage of OLAB suitable for the analyses of protein expression. We used immunohistochemistry to determine protein expression patterns in vivo. OLAB were treated during culture with zoledronate or denosumab and analyzed by immunocytochemistry and western blotting. Collagen 1 was decreased in vivo in patients with MRONJ and in vitro by denosumab. Zoledronate reduced the level of RUNX2 in vitro. However, RANKL was not significantly affected by zoledronate or denosumab. The results of the present study will help us elucidate the cellular mechanisms of MRONJ. Although culture of OLAB with zoledronate and denosumab significantly altered the protein expression patterns, future research is needed to examine the effects of bone scaffolds, biofilms, and additional cell types mimicking in vivo conditions.

Aging: A struggle for beneficial to overcome negative factors made by muscle and bone

Musculoskeletal health is strongly influenced by regulatory interactions of bone and muscle. Recent discoveries have identified a number of key mechanisms through which soluble factors released during exercise by bone exert positive effects on muscle and by muscle on bone. Although exercise can delay the negative effects of aging, these beneficial effects are diminished with aging. The limited response of aged muscle and bone tissue to exercise are accompanied by a failure in bone and muscle communication. Here, we propose that exercise induced beneficial factors must battle changes in circulating endocrine and inflammatory factors that occur with aging. Furthermore, sedentary behavior results in the release of negative factors impacting the ability of bone and muscle to respond to physical activity especially with aging. In this review we report on exercise responsive factors and evidence of modification occurring with aging.

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.

RANKL blockade inhibits cancer growth through reversing the tolerogenic profile of tumor-infiltrating (plasmacytoid) dendritic cells

BACKGROUND

Originally identified for its involvement in bone remodeling, accumulating data emerged in the past years indicating that receptor activator of nuclear factor κB ligand (RANKL) actually acts as a multifunctional soluble molecule that influences various physiological and pathological processes. Regarding its role in carcinogenesis, while direct effects on tumor cell behavior have been precisely characterized, the impact of the RANKL/RANK system (and its inhibition) on the intratumoral immune landscape remains unclear.

METHODS

After various in silico/in situ/in vitro analyses, the immunotherapeutic efficacy of RANKL blockade (alone and in combination with immune checkpoint inhibitors (anti-programmed cell death protein-1 (PD-1)) or doxorubicin/paclitaxel-based chemotherapy) was investigated using different syngeneic mouse models of triple-negative breast cancer (4T1, 67NR and E0771). Isolated from retrieved tumors, 14 immune cell (sub)populations, along with the activation status of antigen-presenting cells, were thoroughly analyzed in each condition. Finally, the impact of RANKL on the functionality of both dendritic cells (DC) and plasmacytoid dendritic cells (pDC) was determined.

RESULTS

A drastic tumor growth inhibition was reproductively observed following RANKL inhibition. Strikingly, this antitumor activity was not detected in immunocompromised mice, demonstrating its dependence on the adaptive immune responses and justifying the diverse enriched signatures linked to immune cell regulation/differentiation detected in RANKLhigh-expressing human neoplasms. Interestingly, neoadjuvant chemotherapy (but not PD-1 checkpoint inhibition) potentiated the anticancer effects of RANKL blockade by priming effector T cells and increasing their infiltration within the tumor microenvironment. Mechanistically, we highlighted that RANKL indirectly promotes regulatory T cell differentiation and suppressive function by inhibiting the mTOR signaling pathway on antigen-presenting cells.

CONCLUSIONS

Taken together, this study provides insight into the role of RANKL/RANK axis in immune tolerance, demonstrates the significant impact of RANKL-dependent impairment of T cell-DC/pDC crosstalk on tumor development and, ultimately, supports that this ligand could be an interesting actionable target for cancer immunotherapy.

LGR4 (GPR48): The Emerging Inter-Bridge in Osteoimmunology

Leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4), a member of the G-protein-coupled receptor (GPCR) family, has been implicated in various regulatory functions across multiple differentiation stages and numerous target sites in bone diseases. Therefore, LGR4 is a potential regulator of nuclear factor-κB ligand (RANKL) during osteoclast differentiation. However, a comprehensive investigation of its functions and applications in bone immunology is lacking. This review discusses the molecular characteristics, signaling pathways, and role of LGR4 in osteoimmunology, with a particular focus on its interactions with RANKL during osteoclast differentiation, while identifying gaps that warrant further research.

Rejuvenating the immune system

Rejuvenation of elementary immune system components has emerged as a promising strategy to deal with increased susceptibility to infections, cancers, autoimmune disorders, and low efficacy to vaccines, frequently accompanying aging. In this context, the thymus has gained significant attention. A recent study by Santamaria et al. reveals that the receptor activator of nuclear factor-κB (RANK)-RANK ligand (RANKL) axis is altered during age related thymic involution, compromising immune responses. Based on their findings, authors propose exogenous RANKL administration as a therapeutic strategy to reinvigorate thymic function and improve T-cell immunity during aging.

Cardio-metabolic-related plasma proteins reveal biological links between cardiovascular diseases and fragility fractures: a cohort and Mendelian randomisation investigation

BACKGROUND

How cardiovascular diseases (CVD) predispose to a higher risk of fragility fractures is not well understood. Both contribute to significant components of disease burden and health expenditure. Poor bone quality, central obesity, sarcopenia, falls, and low grip strength are independent risk factors for hip and other fragility fractures and also for CVD and early death.

METHODS

We used proteomics and a cohort design combined with Mendelian randomisation analysis to understand shared mechanisms for developing CVD and fragility fractures, two significant sources of disease burden and health expenditure. We primarily aimed to discover and replicate the association of 274 cardio-metabolic-related proteins with future rates of hip and any fracture in two separate population-based cohorts, with a total of 12,314 women and men.

FINDINGS

The average age at baseline was 68 years in the discovery cohort of women and 74 years in the mixed-sex replication cohort. During 100,619 person-years of follow-up, 2168 had any fracture, and 538 had a hip fracture. Our analysis resulted in 24 cardiometabolic proteins associated with fracture risk: 20 with hip fracture, 9 with any fracture, and 5 with both. The associations remained even if protein concentrations were measured from specimens taken during preclinical stages of cardio-metabolic diseases, and 19 associations remained after adjustment for bone mineral density. Twenty-two of the proteins were associated with total body fat mass or lean body mass. Mendelian randomisation (MR) analysis supported causality since genetically predicted levels of SOST (Sclerostin), CCDC80 (Coiled-coil domain-containing protein 80), NT-proBNP (N-terminal prohormone brain natriuretic peptide), and BNP (Brain natriuretic peptide) were associated with risk of hip fracture. MR analysis also revealed a possible negative impact on bone mineral density (BMD) by genetically predicted higher levels of SOST, CCDC80, and TIMP4 (Metalloproteinase inhibitor 4). The MR association with BMD was positive for PTX3 (Pentraxin-related protein) and SPP1 (Osteopontin). Genetically predicted higher concentrations of SOST and lower concentrations of SPP1 also conferred a higher risk of falls and lowered grip strength. The genetically determined concentration of nine proteins influenced fat mass, and one influenced lean body mass.

INTERPRETATION

These data reveal biological links between cardiovascular diseases and fragility fractures. The proteins should be further evaluated as shared targets for developing pharmacological interventions to prevent fractures and cardiovascular disease.

FUNDING

The study was supported by funding from the Swedish Research Council (https://www.vr.se; grants No. 2015-03257, 2017-00644, 2017-06100, and 2019-01291 to Karl Michaëlsson) and funding from Olle Engkvist Byggmästares stiftelse (SOEB).

DEC1 deficiency promotes osteoclastic activity by augmenting NFATc1 signaling via transactivation and the Ca2+/calcineurin pathway

We have previously demonstrated that DEC1 promotes osteoblast differentiation. This study aims to evaluate the impact of DEC1 knockout on osteopenic activities, such as osteoclast differentiation and the expression of bone-degrading genes. To gain mechanistic insights, we employed both in vivo and in vitro experiments, utilizing cellular and molecular approaches, including osteoclast differentiation assays and RNA-seq in combination with ChIP-seq. Our results showed that NFATc1, a master regulator of osteoclast differentiation, and PPP3CB, a member of the calcineurin family, were significantly upregulated in DEC1-/- mice. In vitro experiments revealed that osteoclast differentiation significantly increased both the number and size of osteoclasts in DEC1-/- bone marrow macrophages (BMMs) compared to DEC1+/+ BMMs. Additionally, NFATc1 expression was notably higher in DEC1-/- BMMs than in DEC1+/+ BMMs. Overexpression of DEC1 reduced NFATc1 promoter activity, while knockout increased it. Furthermore, intracellular free Ca2+ levels and calcineurin activity were elevated (∼150 %) in DEC1-/- BMMs compared to DEC1+/+ BMMs. Importantly, the use of calcineurin inhibitors and calcium channel blockers effectively abolished the increased osteoclast differentiation observed in DEC1-/- BMMs. In summary, DEC1 deficiency promotes osteoclast differentiation by enhancing NFATc1 signaling through transcriptional regulation and the Ca2+/calcineurin pathway. Clinically, the mRNA levels of DEC1 were reduced by up to 75 % in patients with osteoporosis. The findings of this study establish that inducing DEC1 expression, alongside attenuators of the Ca2+/calcineurin pathway, offers a molecular basis for preventing and treating osteoporosis associated with DEC1 deficiency.

Computed tomography provides a "one-stop-shop" targeted analysis for coronary artery calcification and osteoporosis: a review

The global trend towards longer lifespans has led to an aging population and a rise in the prevalence of diseases that predominantly affect elderly people. Coronary artery calcification (CAC) and osteoporosis (OP) are common in elderly populations. CT scans provide a reliable method to assess and monitor the progression of these diseases. In this review, the relationship between OP and CAC in terms of pathophysiological mechanism, comorbidity risk factors and clinical manifestations is reviewed, with a focus on the advancements in CT imaging, clinical applications and the possibility for "one-stop-shop" for examination.

MTHFD2 promotes osteoclastogenesis and bone loss in rheumatoid arthritis by enhancing CKMT1-mediated oxidative phosphorylation

BACKGROUND

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by disrupted bone homeostasis. This study investigated the effect and underlying mechanisms of one-carbon metabolism enzyme methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) on osteoclast differentiation and bone loss in RA.

METHODS

The expression of MTHFD2 was examined in CD14 + monocytes and murine bone marrow-derived macrophages (BMMs). RNA-sequencing was performed to evaluate the regulatory mechanisms of MTHFD2 on osteoclastogenesis. Extracellular flux assay, JC-1 staining, and transmission electron microscopy were used to detect mitochondrial function and energy metabolism changes during osteoclast formation. Collagen-induced arthritis (CIA) mice were used to evaluate the therapeutic effect of MTHFD2 knockdown on bone loss. Bone volume and osteoclast counts were quantified by μCT and histomorphometry.

RESULTS

Elevated MTHFD2 was observed in RA patients and CIA mice with a positive correlation to bone resorption parameters. During osteoclast formation, MTHFD2 was significantly upregulated in both human CD14 + monocytes and murine BMMs. The application of MTHFD2 inhibitor and MTHFD2 knockdown suppressed osteoclastogenesis, while MTHFD2 overexpression promoted osteoclast differentiation in vitro. RNA-sequencing revealed that MTHFD2 inhibition blocked oxidative phosphorylation (OXPHOS) in osteoclasts, leading to decreased adenosine triphosphate (ATP) production and mitochondrial membrane potential without affecting mitochondrial biogenesis. Mechanistically, inhibition of MTHFD2 downregulated the expression of mitochondrial creatine kinase 1 (CKMT1), which in turn affected phosphocreatine energy shuttle and OXPHOS during osteoclastogenesis. Further, a therapeutic strategy to knock down MTHFD2 in knee joint in vivo ameliorated bone loss in CIA mice.

CONCLUSIONS

Our findings demonstrate that MTHFD2 is upregulated in RA with relation to joint destruction. MTHFD2 promotes osteoclast differentiation and arthritic bone erosion by enhancing mitochondrial energy metabolism through CKMT1. Thus, targeting MTHFD2 may provide a potential new therapeutic strategy for tackling osteoclastogenesis and bone loss in RA.

Polymethoxyflavones and Bone Metabolism

Phytochemicals, such as flavonoids, are bioactive compounds produced by plants, including citrus fruits, that exhibit antioxidant effects on mammalian cells and tissues. Polymethoxyflavones (PMFs) are a family of flavonoids found in the pulp and peel of citrus fruits, and have been reported to have potent antioxidant activity implicated in the prevention of human diseases. Several studies have shown that PMFs have a protective effect on bone resorption in mouse models of diseases, including osteoporosis, rheumatoid arthritis, and periodontal disease. PMFs significantly suppressed the differentiation of osteoclasts (bone resorptive cells) through indirect and direct mechanisms. The indirect effect of PMFs is the suppression of inflammatory mediator production, such as prostaglandin E2 (PGE2), and the reduction of osteoclastic inducers, such as the receptor activator of NF-κB ligand (RANKL), in osteoblasts (bone-forming cells). The direct effect of PMF suppresses osteoclast differentiation and function by inhibiting the NF-κB signaling pathway. In silico molecular docking studies indicated that PMFs target the ATP-binding pocket of IKKβ and inhibit the NF-κB signaling pathway. These findings suggest that PMFs protect against bone destruction by interfering with the NF-κB pathway in osteoblasts and osteoclasts. In this review, we summarize the latest findings regarding the effects of PMFs on various bone resorption-related diseases in mouse models.

Immunohistochemical Evaluation of Bone Remodeling Following Compressive Force on Mandibular Condyle

Excessive mandibular growth is largely affected by genetic factors and its orthodontic management is challenging. The present study utilized histophotometry and aimed to investigate immunohistochemical alterations in rat condyles following posterior mandibular displacement using a fixed intraoral functional appliance. Seventy-two male Wistar rats were divided into two equal groups, experimental and control, each consisting of three equal subgroups. The animals were sacrificed after 30, 60, and 90 days, and their condyles were isolated and examined microscopically for potential immunohistochemical changes. Statistically significant differences in RANKL appeared at days 30 and 60, while noteworthy changes regarding TRAP were evidenced at days 30 and 90. In the experimental group, RANKL decreased statistically significantly between days 60 and 90, while in the control group, the RANKL measured significantly increased at day 90 compared to days 30 and 60 alike. In the experimental group, TRAP appeared significantly decreased at day 60 vs. 30, while at day 90 vs. 60, it was found to be significantly increased. In the control group, there were no significant changes in TRAP. Posterior mandibular displacement may cause immunohistochemical changes in the rat condylar bone, and such outcomes should be considered when planning similar procedures in humans.

Single-cell transcriptomic atlas of the chicken cecum reveals cellular responses and state shifts during Eimeria tenella infection

Eimeria tenella (E. tenella) infection is a major cause of coccidiosis in chickens, leading to significant economic losses in the poultry industry due to its impact on the cecum. This study presents a comprehensive single-cell atlas of the chicken cecal epithelium by generating 7,394 cells using 10X Genomics single-cell RNA sequencing (scRNA-seq). We identified 13 distinct cell types, including key immune and epithelial populations, and characterized their gene expression profiles and cell-cell communication networks. Integration of this single-cell data with bulk RNA-seq data from E. tenella-infected chickens revealed significant alterations in cell type composition and state, particularly a marked decrease in APOB+ enterocytes and an increase in cycling T cells during infection. Trajectory analysis of APOB+ enterocytes uncovered shifts toward cellular states associated with cell death and a reduction in those linked to mitochondrial and cytoplasmic protection when infected with E. tenella. These findings highlight the substantial impact of E. tenella on epithelial integrity and immune responses, emphasizing the parasite's role in disrupting nutrient absorption and energy metabolism. Our single-cell atlas serves as a critical resource for understanding the cellular architecture of the chicken cecum and provides a valuable framework for future investigations into cecal diseases and metabolic functions, with potential applications in enhancing poultry health and productivity.

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.

LGR4 is essential for maintaining β-cell homeostasis through suppression of RANK

OBJECTIVE

Loss of functional β-cell mass is a major cause of diabetes. Thus, identifying regulators of β-cell health is crucial for treating this disease. The Leucine-rich repeat-containing G-protein-coupled receptor (GPCR) 4 (LGR4) is expressed in β-cells and is the fourth most abundant GPCR in human islets. Although LGR4 has regenerative, anti-inflammatory, and anti-apoptotic effects in other tissues, its functional significance in β-cells remains unknown. We have previously identified Receptor Activator of Nuclear Factor Kappa B (NFκB) (RANK) as a negative regulator of β-cell health. In this study, we assessed the regulation of Lgr4 in islets, and the role of LGR4 and LGR4/RANK stoichiometry in β-cell health under basal and stress-induced conditions, in vitro and in vivo.

METHODS

We evaluated Lgr4 expression in mouse and human islets in response to acute (proinflammatory cytokines), or chronic (high fat fed mice, db/db mice, and aging) stress. To determine the role of LGR4 we employed in vitro Lgr4 loss and gain of function in primary rodent and human β-cells and examined its mechanism of action in the rodent INS1 cell line. Using Lgr4fl/fl and Lgr4fl/fl/Rankfl/fl × Ins1-Cre mice we generated β-cell-specific conditional knockout (cko) mice to test the role of LGR4 and its interaction with RANK in vivo under basal and stress-induced conditions.

RESULTS

Lgr4 expression in rodent and human islets was reduced by multiple stressors. In vitro, Lgr4 knockdown decreased proliferation and survival in rodent β-cells, while overexpression protected against cytokine-induced cell death in rodent and human β-cells. Mechanistically, LGR4 protects β-cells by suppressing RANK- Tumor necrosis factor receptor associated factor 6 (TRAF6) interaction and subsequent activation of NFκB. Lgr4cko mice exhibit normal glucose homeostasis but increased β-cell death in both sexes and decreased β-cell proliferation and maturation only in females. Male Lgr4cko mice under stress displayed reduced β-cell proliferation and a further increase in β-cell death. The impaired β-cell phenotype in Lgr4cko mice was rescued in Lgr4/Rank double ko (dko) mice. Upon aging, both male and female Lgr4cko mice displayed impaired β-cell homeostasis, however, only female mice became glucose intolerant with decreased plasma insulin.

CONCLUSIONS

These data demonstrate a novel role for LGR4 as a positive regulator of β-cell health under basal and stress-induced conditions, through suppressing the negative effects of RANK.

OPG and BAFF as predictive biomarkers of the severity of SARS-CoV-2 infection

Molecules of the tumour necrosis factor superfamily (TNFSF) are key players in immune regulation; an increase in some TNFSF molecules has been reported during severe COVID-19. In this study, we profiled and evaluated TNFSF members in the serum of COVID-19 vaccine-naïve patients to identify potential biomarkers associated with disease severity. Our data show that TRAIL serum levels are lower in severely affected patients than those mildly affected by COVID-19 (AUC 0.8, p = 0.0003). On the contrary, OPG and BAFF serum levels are higher in severe COVID-19 compared to mild COVID-19 cases (AUC 0.8, p = 0.0001; AUC 0.7, p = 0.0012; respectively) and moderate COVID-19 cases (OPG p < 0.01), BAFF (p < 0.05). At the transcriptional level, TRAIL, OPG and BAFF are elevated in severe compared to mild COVID-19 cases, with OPG and BAFF also higher in moderate compared to mild COVID-19 patients. Additionally, we found that APRIL, LIGHT, CD30L and CD40L protein-levels are higher in COVID-19 patients compared to healthy donors but not significantly different between various COVID-19 clinical statuses. Finally, we found that TNF-α, TNF-β, RANKL and TWEAK protein levels were not affected during COVID-19. Our work identifies OPG and BAFF as potential biomarkers and therapeutic targets for preventing severe COVID-19. Due to the opposite contradictory levels of TRAIL (protein/transcriptional level), its role during COVID-19 should be elucidated and clarified with more in-depth studies.

Glucocorticoids on bone remodeling in systemic lupus erythematosus mice

BACKGROUND

Systemic lupus erythematosus requires glucocorticoids for management. This study investigates how glucocorticoids influence bone in a SLE mouse model, focusing on bone mineral density (BMD), microstructure, and remodeling markers.

METHODS

MRL/lpr and C57BL/6 mice were administered dexamethasone or saline as a control for 4-weeks. Bone assessments included analyses of BMD, bone structure, and serum levels of RANKL and OPG.

RESULTS

Dexamethasone decreased BMD and altered cortical and trabecular bone thickness in both MRL/lpr and C57BL/6 mice. In C57BL/6 mice, cortical bone exhibited increased catabolism while trabecular bone showed signs of increased anabolism, whereas MRL/lpr mice did not show significant changes in bone turnover. Both strains experienced weight loss, with a significant decrease in femur length observed only in C57BL/6 mice. Dexamethasone exacerbated BMD reduction in MRL/lpr mice and halted its increase in C57BL/6 mice. C57BL/6 mice exhibited notable changes in cortical and trabecular bone structure, while MRL/lpr mice didn't. After receiving dexamethasone, both strains showed higher serum RANKL levels, especially in C57BL/6 mice. OPG decreased in both strains.

CONCLUSION

Both glucocorticoids and SLE contribute to abnormal bone remodeling through RANKL/OPG pathway.

IMPACT

Glucocorticoid (GC) treatment in a mouse model of systemic lupus erythematosus (SLE) leads to significant changes in bone parameters, including decreased bone mineral density (BMD) and alterations in bone structure. Those change are associated with the modulation of RANKL and OPG expression. Both GC and inflammation in SLE contribute to BMD reduction, and GC may have a certain protective effect on bone in the early stage of chronic inflammation. GC can upregulate RANKL expression and downregulate OPG expression in vivo. During a state of chronic inflammation, RANKL expression increases. However, OPG may not exert a significant influence on inflammatory stimulation.

The Role of Osteoprotegerin in Breast Cancer: Genetic Variations, Tumorigenic Pathways, and Therapeutic Potential

INTRODUCTION

Osteoprotegerin (OPG), encoded by the TNFRSF11B gene, is linked to the development of breast cancer via several pathways, including interactions with the receptor activator of nuclear factor-κB (RANK) ligands, apoptosis-inducing proteins like TRAIL, and genetic variations such as single nucleotide polymorphisms (SNPs), directly altering gene expression. This review aims to investigate the role of OPG expression in breast cancer.

METHODS

A comprehensive literature search was conducted using PubMed Medline, Google Scholar, and ScienceDirect. Only full-text English publications from inception to September 2024 were included.

RESULTS

Studies have demonstrated that certain SNPs in the OPG gene, specifically rs3102735 and rs2073618, are linked to a higher risk of breast cancer development. Additionally, OPG's function as a TRAIL decoy receptor may inhibit the death of cancer cells. Furthermore, OPG in the serum and its interactions with BRCA mutations are being investigated for their potential influence on breast cancer progression. Studies have found that OPG promotes tumorigenesis by enhancing cell proliferation, angiogenesis, and aneuploidy in normal mammary epithelial cells. Moreover, OPG mediates the tumor-promoting effects of interleukin-1 beta and may serve as a biomarker for breast cancer risk, particularly in BRCA1 mutation carriers, through its role in dysregulated RANK signaling. Lastly, the use of recombinant OPG in mouse models has been found to exert anti-tumor effects.

CONCLUSIONS

In this review, the role of OPG in breast cancer is examined. OPG has a multifaceted role in breast cancer tumorigenesis and exerts its effects through genetic variations (SNPs), interactions with TNF-related apoptosis-inducing ligand (TRAIL), and the modulation of the pro-tumorigenic microenvironment effects of angiogenesis, cell survival, and metastasis. Additionally, OPG's dual role as a tumor suppressor and promoter serves as a possible therapeutic target to enhance apoptosis, limit bone metastasis, and modulate the tumor microenvironment. Whilst much is now known, further studies are necessary to fully delineate the role of OPG.

The SIRT5-JIP4 interaction promotes osteoclastogenesis by modulating RANKL-induced signaling transduction

Receptor activator of nuclear factor kappa-B ligand (RANKL) initiates a complex signaling cascade that is crucial for inducing osteoclast differentiation and activation. RANKL-induced signaling has been analyzed in detail, and the involvement of TNF receptor-associated factor 6 (TRAF6), calmodulin-dependent protein kinase (CaMK), NF-κB, mitogen-activated protein kinase (MAPK), activator protein-1 (AP-1), and molecules that contain an immunoreceptor tyrosine-based activation motif (ITAM) has been reported. However, the precise molecular steps that regulate RANKL signaling remain largely unknown. Here, we revealed the indispensable role of a class III histone deacetylase (SIRT5) in the processes of RANKL-induced osteoclast differentiation and activation. SIRT5 expression in osteoclasts was increased during osteoclastogenesis upon stimulation with RANKL. The RANKL-induced signaling activation was suppressed in SIRT5-deficient osteoclasts but enhanced by SIRT5 overexpression. Mice with global or conditional monocytic lineage knockout of SIRT5 had increased bone mass and reduced osteoclast numbers. In the cytoplasm, SIRT5 interacted with the scaffold protein JNK-interacting protein 4 (JIP4) to finely regulate MAPK signaling, which was critical for osteoclast differentiation and activation. Pharmacological inhibition of the catalytic activity of SIRT5 effectively reversed bone loss in ovariectomized mice. Taken together, the results of this study reveal that the SIRT5-JIP4 axis is a novel positive regulator that finely regulates RANKL-induced osteoclast differentiation and suggest that targeting this axis is a therapeutic strategy for preventing osteoporotic bone loss.

Deep learning and genome-wide association meta-analyses of bone marrow adiposity in the UK Biobank

Bone marrow adipose tissue is a distinct adipose subtype comprising more than 10% of fat mass in healthy humans. However, the functions and pathophysiological correlates of this tissue are unclear, and its genetic determinants remain unknown. Here, we use deep learning to measure bone marrow adiposity in the femoral head, total hip, femoral diaphysis, and spine from MRI scans of approximately 47,000 UK Biobank participants, including over 41,000 white and over 6300 non-white participants. We then establish the heritability and genome-wide significant associations for bone marrow adiposity at each site. Our meta-GWAS in the white population finds 67, 147, 134, and 174 independent significant single nucleotide polymorphisms, which map to 54, 90, 43, and 100 genes for the femoral head, total hip, femoral diaphysis, and spine, respectively. Transcriptome-wide association studies, colocalization analyses, and sex-stratified meta-GWASes in the white participants further resolve functional and sex-specific genes associated with bone marrow adiposity at each site. Finally, we perform a multi-ancestry meta-GWAS to identify genes associated with bone marrow adiposity across the different bone regions and across ancestry groups. Our findings provide insights into BMAT formation and function and provide a basis to study the impact of BMAT on human health and disease.

Prenatal toxicity of L-mimosine in Wistar rats

L-Mimosine is the main active component of the plant Leucaena leucocephala. Due to its metal-chelating mechanism, it interacts with various metabolic pathways in living organisms, making it a potential pharmacological target, although it also leads to toxicity. The present study aimed to investigate the transplacental passage of L-mimosine and its effects on embryofetal development. Pregnant Wistar rats were divided into control groups (CO2; n = 8 or CO3; n = 6, according to experimental design 2 or 3) that received only the vehicle, and groups that received doses of 60 (n = 9), 100 (n = 8), 140 (n = 9), and 240 (n = 7) mg/kg of L-mimosine from gestational day (GD) 6-19. For the transplacental analysis, five rats were used: two as controls and three treated with a dose of 140 mg/kg L-mimosine from GD12 to 14. All the animals received food and water ad libitum. The parameters analyzed were body weight gain; water and food consumption; serum biochemistry; blood cell counts; reproductive indices; and histopathological, visceral and skeletal analyses of the fetuses. In the groups that received doses of 60, 100, and 140 mg/kg, alterations (P < 0.05) in the skeletal development of the fetuses were observed. In the 240 mg/kg group, a decrease (P < 0.05) in total food consumption; a decrease (P < 0.05) in absolute leukocyte and neutrophil counts; alterations (P < 0.05) in the levels of ALT, GGT, and creatinine enzymes; a decrease (P < 0.05) in the relative weight of the thymus along with a loss of the corticomedullary distinction; coalescence of lymphoid follicles in the spleen; and skeletal and visceral alterations and alopecia were observed. L-Mimosine was detected in the amniotic fluid of the rats. These results demonstrate the complex action of L-mimosine, leading to toxic effects on both dams and fetuses, highlighting the risk of exposure to this substance during the perinatal period, which negatively impacts embryo/fetal and neonatal growth and development.

Combination of Cannabidiol with Taurine Synergistically Treated Periodontitis in Rats

The active component in cannabis, cannabidiol (CBD), was first isolated from the hemp plant in 1940. Chronic pain, inflammation, migraines, depression, and anxiety have long been treated with CBD. The fundamental mechanisms of CBD's effects on periodontal inflammation have yet to be fully understood. The amino sulfonic acid taurine is a substance that naturally exists in the body and is an inhibitory modulator of inflammation. This study examined the effects of CBD, taurine, and their combination on inflammatory cytokines and periodontitis in vivo. To assess the expression of inflammatory markers of iNOS, COX-2, TNF-α, and IL-1β, as well as TRAP count and resorbed pit areas, CBD and taurine were applied to RAW264.7 cells. The following groups of 45 Sprague-Dawley rats each were created: control (healthy), vehicle (induced periodontitis), low- and high-dose-CBD with taurine which were each treated for an additional 21 days. Rat teeth were obtained and subjected to histomorphometric studies. The combination of the two significantly decreased the expression of inflammatory markers TNF-α and IL-1β and the amount of TRAP+ cells and resorbed pit areas. Among rats with P. gingivalis-induced periodontitis, the alveolar bone resorption levels, periodontal pocket depth, and distance between cementoenamel junction (CEJ) and alveolar bone crest (ABC) were significantly reduced after treatment with CBD and taurine, suggesting that combining CBD with taurine could be a novel therapeutic agent against periodontal disease.

Pediatric Fracture Remodeling: From Wolff to Wnt

Pediatric fracture remodeling is a complex mechanobiological process in which a team of cells, including osteoclasts, osteoblasts, and osteocytes, responds to cytokine and mechanical signals to synthesize new bone in areas of high stress (concavity of a fracture) and remove older redundant bone in areas of low stress (convexity and medullary canal). Piezo1 mechanoreceptors and other pressure-sensitive membrane proteins perceive and convert mechanical strains into intracellular chemical signals. Cytokines are peptides that bind to cell membrane receptors and influence cell functions. Bone morphogenetic proteins and Wnt are the major osteogenic cytokines. Macrophage colony-stimulating factor and receptor activator of nuclear factor κB ligand (RANKL) are the major osteoclastic cytokines. The combination of mechanical stresses and cytokine concentrations stimulates osteoclasts to resorb bone and osteoblasts to make new bone, resulting in remodeling that restores bone strength and structure.

Unraveling the Mechanism of Impaired Osteogenic Differentiation in Osteoporosis: Insights from ADRB2 Gene Polymorphism

Osteoporosis is characterized by increased resorption and decreased bone formation; it is predominantly influenced by genetic factors. G-protein coupled receptors (GPCRs) play a vital role in bone homeostasis, and mutations in these genes are associated with osteoporosis. This study aimed to investigate the impact of single nucleotide polymorphism (SNP) rs1042713 in the ADRB2 gene, encoding the beta-2-adrenergic receptor, on osteoblastogenesis. Herein, using quantitative polymerase chain reaction, western immunoblotting, immunofluorescence assays, and flow cytometry, we examined the expression of ADRB2 and markers of bone matrix synthesis in mesenchymal stem cells (MSCs) derived from osteoporosis patient (OP-MSCs) carrying ADRB2 SNP in comparison with MSCs from healthy donor (HD-MSCs). The results showed significantly reduced ADRB2 expression in OP-MSCs at both the mRNA and protein levels, alongside decreased type 1 collagen expression, a key bone matrix component. Notably, OP-MSCs exhibited increased ERK kinase expression during differentiation, indicating sustained cell cycle progression, unlike that going to HD-MSC. These results provide novel insights into the association of ADRB2 gene polymorphisms with osteogenic differentiation. The preserved proliferative activity of OP-MSCs with rs1042713 in ADRB2 contributes to their inability to undergo effective osteogenic differentiation. This research suggests that targeting genetic factors may offer new therapeutic strategies to mitigate osteoporosis progression.

Immunotherapy in the management of inflammatory bone loss in osteoporosis

Osteoporosis, a progressive skeletal disorder characterized by decreased bone mass and increased fracture risk, has traditionally been treated with pharmacological agents targeting bone remodeling. However, emerging research highlights the critical role of immune system in regulating bone metabolism, introducing the concept of Osteoimmunology. Chronic low-grade inflammation is now recognized as a significant contributor to osteoporosis, particularly in postmenopausal women and the elderly. Immune cells, such as T cells and B cells, and their secreted cytokines directly influence bone resorption and formation, tipping the balance toward net bone loss in inflammatory environments. Immunotherapy, a treatment modality traditionally associated with cancer and autoimmune diseases, is now gaining attention in the management of osteoporosis. By targeting immune dysregulation and reducing inflammatory bone loss, immunotherapies offer a novel approach to treating osteoporosis that goes beyond merely inhibiting bone resorption or promoting bone formation. This therapeutic strategy includes monoclonal antibodies targeting inflammatory cytokines, cell-based therapies to enhance the function of regulatory T and B cells, and interventions aimed at modulating immune pathways linked to bone health. This chapter reviews the emerging role of immunotherapy in addressing inflammatory bone loss in osteoporosis. Present chapter also explores the underlying immune mechanisms contributing to bone degradation, current immunotherapeutic strategies under investigation, and the potential of these approaches to revolutionize the management of osteoporosis.

Exploring the Osteoinductive Potential of Bacterial Pyomelanin Derived from Pseudomonas aeruginosa in a Human Osteoblast Model

Alkaptonuria (AKU) is a genetically determined disease associated with disorders of tyrosine metabolism. In AKU, the deposition of homogentisic acid polymers contributes to the pathological ossification of cartilage tissue. The controlled use of biomimetics similar to deposits observed in cartilage during AKU potentially may serve the development of new bone regeneration therapy based on the activation of osteoblasts. The proposed biomimetic is pyomelanin (PyoM), a polymeric biomacromolecule synthesized by Pseudomonas aeruginosa. This work presents comprehensive data on the osteoinductive, pro-regenerative, and antibacterial properties, as well as the cytocompatibility, of water-soluble (PyoMsol) or water-insoluble (PyoMinsol) PyoM. Both variants of PyoM support osteoinductive processes as well as the maturation of osteoblasts in cell cultures in vitro due to the upregulation of bone-formation markers, osteocalcin (OC), and alkaline phosphatase (ALP). Furthermore, the cytokines involved in these processes were elevated in cell cultures of osteoblasts exposed to PyoM: tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-10. The PyoM variants are cytocompatible in a wide concentration range and limit the doxorubicin-induced apoptosis of osteoblasts. This cytoprotective PyoM activity is correlated with an increased migration of osteoblasts. Moreover, PyoMsol and PyoMinsol exhibit antibacterial activity against staphylococci isolated from infected bones. The osteoinductive, pro-regenerative, and antiapoptotic effects achieved through PyoM stimulation prompt the development of new biocomposites modified with this bacterial biopolymer for medical use.

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.

Chronic toxic effects of chloroxylenol exposure on Rana chensinensis: Insights from endochondral ossfication

Chloroxylenol (para‑chloro-meta-xylenol, PCMX), is a widely used antimicrobial agent and can remain in the aquatic environment. Although toxicity studies related to PCMX on the aquatic animals like zebrafish and Brachionus koreanus have been reported, there are few reports in the ecological risk of amphibians. In this study, the toxicity of different concentration (143, 14.3, 1.43 μg/L) of PCMX treatments on the endochondral ossification and body condition of Rana chensiensis tadpoles was investigated at environmentally relevant concentrations during metamorphosis. The chronic exposure of PCMX decreased bone length and ossification of limbs, caused changes of thyroid gland structure and ossification related gene expression levels. Besides, we found that R. chensiensis developed rheumatoid arthritis. Therefore, these results provided valuable evidence that the ecological risk of PCMX that will negatively affect the body condition, thyroid hormones homeostasis and skeletal development of R. chensiensis tadpoles.

Contribution of macrophage polarization in bone metabolism: A literature review

Macrophage polarization divides macrophages into two main cell subpopulations, classically and alternatively activated macrophages (M1 and M2, respectively). M1 polarization promotes osteoclastogenesis, while M2 polarization promotes osteogenesis. The physiological homeostasis of bone metabolism involves a high dynamic balance between osteoclastic-mediated bone resorption and formation. Reportedly, M1/M2 imbalance causes the onset and persistence of inflammation-related bone diseases. Therefore, understanding the research advances in functions and roles of macrophages in such diseases will provide substantial guidance for improved treatment of bone diseases. In this review, we underscore and summarize the research advances in macrophage polarization, and bone-related diseases, such as rheumatoid arthritis, osteoarthritis, and osteoporosis, over the last 5 years. Our findings showed that targeting macrophages and balancing macrophage polarization can effectively reduce inflammation and decrease bone destruction while promoting bone formation and vascular repair. These results indicate that regulating macrophage and macrophage polarization to restore homeostasis is a prospective approach for curing bone-related diseases.

Extra-osseous Roles of the RANK-RANKL-OPG Axis with a Focus on Skeletal Muscle

PURPOSE OF REVIEW

This review aims to consolidate recent observations regarding extra-osseous roles of the RANK-RANKL-OPG axis, primarily within skeletal muscle.

RECENT FINDINGS

Preclinical efforts to decipher a common signalling pathway that links the synchronous decline in bone and muscle health in ageing and disease disclosed a potential role of the RANK-RANKL-OPG axis in skeletal muscle. Evidence suggests RANKL inhibition benefits skeletal muscle function, mass, fibre-type switching, calcium homeostasis and reduces fall incidence. However, there still exists ambiguity regarding the exact mechanistic actions and subsequent functional improvements. Other potential RANK-RANKL-OPG extra-osseous roles include regulation of neural-inflammation and glucose metabolism. Growing evidence suggests the RANK-RANKL-OPG axis may play a regulatory role in extra-osseous tissues, especially in skeletal muscle. Targeting RANKL may be a novel therapy in ameliorating loss of muscle mass and function. More research is warranted to determine the causality of the RANK-RANKL-OPG axis in extra-osseous tissues, especially those affected by aging.

Generation of BT-Amide, a Bone-Targeted Pyk2 Inhibitor, Effective via Oral Administration, for the Prevention of Glucocorticoid-Induced Bone Loss

Glucocorticoid-induced osteoporosis (GIOP) is the leading cause of iatrogenic osteoporosis due to the widespread clinical use of glucocorticoids (GC) as immunosuppressants. Previous research identified the proline-rich tyrosine kinase 2, Pyk2, as a critical mediator of GC-induced bone loss, and that blocking Pyk2 could protect the skeleton from adverse GC actions. However, systemic administration of current Pyk2 inhibitors causes harmful side effects, such as skin lesions. To address this, we developed bone-targeted (BT) Pyk2 inhibitors by conjugating them with bisphosphonates (BP), ensuring adherence to the bone matrix and reducing impact on noncalcified tissues. We synthesized BT-Amide by linking a derivative of TAE-226, a Pyk2 inhibitor, with alendronic acid. Oral administration (gavage) of BT-Amide prevented GC-induced bone loss in mice without causing skin lesions, or elevation of any organ toxicity markers. These findings introduce BT-Amide as the first orally effective bone-targeted Pyk2 inhibitor for preventing GC-induced bone loss while minimizing off-target effects.

Xanthohumol: Anti-Inflammatory Effects in Mechanically Stimulated Periodontal Ligament Stem Cells

BACKGROUND/OBJECTIVES

Initial sterile inflammation is an essential molecular process in the periodontium during orthodontic tooth movement. A better understanding and possible modulations of these processes are of great interest to develop individual therapies for special patient groups. The prenylated plant polyphenol xanthohumol (XN) could have modulating effects as it has shown anti-inflammatory and angiogenesis-inhibiting effects in various cell lines. This study investigated the anti-inflammatory properties of XN in an in vitro model of compressively stimulated human periodontal ligament stem cells (hPDLSCs), which have a different function in the periodontium than the previously used cementoblasts.

METHODS

The expression of inflammatory markers at the mRNA and protein levels and the regulation of central kinases were investigated.

RESULTS

XN showed a dose-dependent influence on cell viability. Low concentrations between 0.2 and 4 µM showed positive effects, while 8 µM caused a significant decrease in viability after 24 h. Mechanical stimulation induced an upregulation of pro-inflammatory gene (IL-6, COX2) and protein (IL-6) expression. Here, XN significantly reduced stimulation-related IL-6 mRNA and gene expression. Furthermore, the phosphorylation of AKT and ERK was upregulated by mechanical stimulation, and XN re-established phosphorylation at a level similar to the control.

CONCLUSIONS

We demonstrated a selective anti-inflammatory effect of XN in hPDLSCs. These findings provide the basis for further investigation of XN in the modulation of inflammatory responses in orthodontic therapy and the treatment of periodontal inflammation.

Associations Among Estrogens, the Gut Microbiome and Osteoporosis

PURPOSE OF THE REVIEW

The purpose of this Review was to summarize the evidence on the associations among estrogen status, cellular senescence, the gut microbiome and osteoporosis.

RECENT FINDINGS

Indicate that osteoporosis is a global public health problem that impacts individuals and society. In postmenopausal women, a decrease in estrogen levels is associated with a decrease in gut microbial diversity and richness, as well as increased permeability of the gut barrier, which allows for low-grade inflammation. The direct effects of estrogen status on the association between bone and the gut microbiome were observed in untreated and treated ovariectomized women. In addition to the direct effects of estrogens on bone remodeling, estrogen therapy could reduce the risk of postmenopausal osteoporosis by preventing increased gut epithelial permeability, bacterial translocation and inflammaging. However, in studies comparing the gut microbiota of older women, there were no changes at the phylum level, suggesting that age-related comorbidities may have a greater impact on changes in the gut microbiota than menopausal status does. Estrogens modify bone health not only by directly influencing bone remodeling, but also indirectly by influencing the gut microbiota, gut barrier function and the resulting changes in immune system reactivity.

Chamomile Tincture and Lidocaine Hydrochloride Gel Ameliorates Periodontitis: A Preclinical Study

Background/Objectives: Periodontitis is a common oral disease marked by gingival inflammation and alveolar bone loss. This study evaluated the efficacy of chamomile tincture and lidocaine hydrochloride (CLH) gel in mitigating periodontal inflammation and bone loss and uncovered the molecular mechanisms involved, both in vitro and in vivo. Methods: A periodontitis model was induced in Sprague Dawley rats by ligating the mandibular first molars. Sixty rats were divided into four groups: control (C), periodontitis (PD), periodontitis + CLH gel once daily (G1), and periodontitis + CLH gel thrice daily (G3). Clinical, micro-computed tomography (micro-CT), biological, and histological evaluations were performed, focusing on osteoclastogenesis, osteogenesis, and inflammatory cytokine production. The effect of CLH gel on inflammatory responses in RAW264.7 cells was also assessed through co-culture assays under Porphyromonas gingivalis (P. gingivalis) infection, with RNA-sequencing, qPCR, and Western blot analyses to explore underlying mechanisms. Results: CLH gel significantly reduced gingival and systemic inflammation and mitigated bone loss by enhancing the bone volume to tissue volume ratio and trabecular thickness via the RANKL/OPG axis in rats. The G3 group showed marked reductions in osteoclasts and increases in osterix-positive cells compared to other groups. In vitro, CLH gel reduced the inflammatory phenotype of macrophages in the periodontitis microenvironment by modulating Type II interferon (IFN-γ) networks. Conclusions: CLH gel reduced inflammation and bone loss in rat periodontitis, promoting osteogenesis and inhibiting osteoclastogenesis. It also suppressed macrophage inflammation via Type II interferon networks under P. gingivalis stimulation. These findings suggest that CLH gel has potential as an adjunctive therapy for periodontitis.

Exploring cytokines dynamics: Uncovering therapeutic concepts for metabolic disorders in postmenopausal women- diabetes, metabolic bone diseases, and non-alcohol fatty liver disease

Menopause is an age-related change that persists for around one-third of a woman's life. Menopause increases the risk of metabolic illnesses such as diabetes, osteoporosis (OP), and nonalcoholic fatty liver disease (NAFLD). Immune mediators (pro-inflammatory cytokines), such as interleukin-1 (IL-1), IL-6, IL-17, transforming growth factor (TGF), and tumor necrosis factor (TNF), exacerbate the challenges of a woman undergoing menopause by causing inflammation and contributing to the development of these metabolic diseases in postmenopausal women. Furthermore, studies have shown that anti-inflammatory cytokines such as interleukin-1 receptor antagonists (IL-1Ra), IL-2, and IL-10 have a double-edged effect on diabetes and OP. Likewise, several interferon (IFN) members are double-edged swords in the OP. Therefore, addressing these immune mediators precisely may be an approach to improving the health of postmenopausal women. Hence, considering the significant changes in these cytokines, the present review focuses on the latest findings concerning the molecular mechanisms by which pro- and anti-inflammatory cytokines (interleukins) impact postmenopausal women with diabetes, OP, and NAFLD. Furthermore, we comprehensively discuss the therapeutic approaches that identify cytokines as therapeutic targets, such as hormonal therapy, physical activities, natural inhibitors (drugs), and others. Finally, this review aims to provide valuable insights into the role of cytokines in postmenopausal women's diabetes, OP, and NAFLD. Deeply investigating the mechanisms and therapeutic interventions involved will address the characteristics of immune mediators (cytokines) and improve the management of these illnesses, thereby enhancing the general quality of life and health of the corresponding populations of women.

Vasoactive intestinal peptide exerts an osteoinductive effect in human mesenchymal stem cells

Several neuropeptides present in bone tissues, produced by nerve fibers and bone cells, have been reported to play a role in regulating the fine-tuning of osteoblast and osteoclast functions to maintain bone homeostasis. This study aims to characterize the influence of the neuropeptide vasoactive intestinal peptide (VIP) on the differentiation process of human mesenchymal stem cells (MSCs) into osteoblasts and on their anabolic function. We describe the mRNA and protein expression profile of VIP and its receptors in MSCs as they differentiate into osteoblasts, suggesting the presence of an autocrine signaling pathway in these cells. Our findings reveal that VIP enhances the expression of early osteoblast markers in MSCs under osteogenic differentiation and favors both bone matrix formation and proper cytoskeletal reorganization. Finally, our data suggest that VIP could be exerting a direct modulatory role on the osteoblast to osteoclast signaling by downregulating the receptor activator of nuclear factor-κB ligand/osteoprotegerin ratio. These results highlight the potential of VIP as an osteoinductive differentiation factor, emerging as a key molecule in the maintenance of human bone homeostasis.