Receptor activator of NF-kappa B and osteoprotegerin expression by human microvascular endothelial cells, regulation by inflammatory cytokines, and role in human osteoclastogenesis

The Role of the Receptor Activator of Nuclear Factor Kappa-B Ligand/Osteoprotegerin Ratio in Vascular Diseases: A Therapeutic Approach

Cardiovascular and bone diseases contribute independently to mortality and global health. The exact mechanisms involved in the pathophysiology shared between bone and vascular diseases are not well defined. Endothelial cells and osteoblasts communicate during osteogenesis, thus establishing a connection between angiogenesis and osteogenesis. One shared mechanism may involve osteoprotegerin (OPG) and its ligand Receptor Activator of NF-κB Ligand (RANKL). The RANKL/OPG ratio is an important modulator for the skeletal, immunological, and vascular systems. OPG levels are elevated due to either osteogenic causes or inflammatory responses in the vasculature. The data obtained from clinical and in vitro studies support the role of the RANKL/OPG ratio as a potential marker for the progression of endothelial damage. Therefore, determining the therapeutic approaches for the targeting RANKL/OPG ratio and evaluating its usage as a biomarker in cardiovascular and bone pathophysiology are needed. By integrating the protective and disease-causing role of OPG with its ligand, this review outlines the role of the RANKL/OPG ratio at the molecular level. We also consider targeted therapeutic approaches.

Global knowledge mapping of receptor activator of nuclear factor kappa-B ligand in osteoporotic fractures: a bibliometric analysis (2001-2024)

Background

Receptor activator of nuclear factor kappa-B ligand (RANKL) plays a critical role in bone metabolism and the pathogenesis of osteoporotic fractures. This study aims to conduct a bibliometric analysis of global research pertaining to RANKL and osteoporotic fractures to identify key trends, influential studies, and collaborative networks.

Methods

A literature search was conducted to identify articles found in the Web of Science Core Collection database regarding RANKL and osteoporotic fractures from 2001 to 2024. A bibliometric analysis was performed using VOSviewer, CiteSpace, and R 4.3.3 for the publication volume, country and institution contributions, journal impact, author influence, and research hotspots.

Results

A total of 214 articles were analyzed. Publication rates have steadily increased, with a peak of 21 papers in 2020. The U.S., China, and South Korea were the top contributing countries, and leading institutions included Harvard University and Dankook University. The Journal of Bone and Mineral Research, Osteoporosis International, and Bone were the journals of highest impact. At the level of authors, Heiss-Christian published the highest number and Christiansen-Claus had the strongest citation impact (1,368 citations). Research evolved from basic biological mechanisms (2001-2010) through clinical applications (2011-2017) to recent renewed interest in fundamental RANKL biology (2018-2024). Key research hotspots included postmenopausal osteoporosis, bone mineral density, and osteoclast differentiation, with emerging focus on RANKL's role beyond skeletal metabolism.

Conclusion

This bibliometric analysis provides a comprehensive overview of RANKL research in osteoporotic fractures, highlighting key priorities for future investigation. Future studies should prioritize understanding RANKL's broader physiological roles, developing better predictive markers, and optimizing personalized treatment strategies.

Modulation of the hepatic RANK-RANKL-OPG axis by combined C5 and CD14 inhibition in a long-term polytrauma model

Background

Polytrauma and hemorrhagic shock can lead to direct and indirect liver damage involving intricate pathophysiologic mechanisms. While hepatic function has been frequently highlighted, there is minimal research on how the receptor activator of the NF-κB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) system is regulated in the liver following trauma. Furthermore, cross-talking complement and toll-like-receptor (TLR) systems can contribute to the posttraumatic response. Therefore, we investigated the hepatic consequences of polytrauma focusing on the RANK-RANKL-OPG axis, and evaluated the effects of a dual blockade of complement factor C5 and TLR-cofactor CD14 on hepatic features.

Methods

The established pig model of polytrauma (PT) and hemorrhagic shock included pulmonary contusion, hepatic dissection, and bilateral femur fractures, surgically addressed either by external fixation (Fix ex) or intramedullary nailing (Nail). Four groups were investigated: 1) sham animals; 2) PT treated by Fix ex (Fix ex); 3) PT by Nail (Nail); or 4) PT by Nail plus combined C5/CD14 inhibition (Nail+Therapy). Serum samples were obtained between 0 - 72 h, and liver samples at 72 h after PT. Liver tissues were histologically scored and subjected to RT-qPCR-analyses, immunohistochemistry and ELISAs to evaluate the posttraumatic hepatic response with a focus on the RANK-RANKL-OPG system.

Results

Following PT, the liver injury score of the Nail+Therapy group was significantly lower than in the Fix ex or Nail group without immunomodulation (p<0.05). Similarly, the degree of necrosis, lobular stasis, and inflammation were significantly reduced when treated with C5/CD14-inhibitors. Compared to the Nail group, AST serum concentrations were significantly decreased in the Nail+Therapy group after 72 h (p<0.05). PCR analyses indicated that RANK, RANKL, and OPG levels in the liver were increased after PT in the Nail group compared to lower levels in the Nail+Therapy group. Furthermore, liver tissue analyses revealed increased RANK protein levels and cellular immunostaining for RANK in the Nail group, both of which were significantly reduced in the case of C5/CD14-inhibition (p<0.05).

Conclusion

Following experimental PT, dual inhibition of C5/CD14 resulted in altered, mainly reduced hepatic synthesis of proteins relevant to bone repair. However, a comprehensive investigation of the subsequent effects on the liver-bone axis are needed.

Osteoprotegerin (OPG) and its ligands RANKL and TRAIL in falciparum, vivax and knowlesi malaria: correlations with disease severity, and B cell production of OPG

Osteoprotegerin (OPG) is a soluble decoy receptor for receptor activator of NF-ƙB ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL), and is increasingly recognised as a marker of poor prognosis in a number of diseases. Here we demonstrate that in Malaysian adults with falciparum and vivax malaria, OPG is increased, and its ligands TRAIL and RANKL decreased, in proportion to disease severity. In volunteers experimentally infected with P. falciparum and P. vivax, RANKL was suppressed, while TRAIL was unexpectedly increased, suggesting binding of OPG to RANKL prior to TRAIL. We also demonstrate that P. falciparum stimulates B cells to produce OPG in vitro, and that B cell OPG production is increased ex vivo in patients with falciparum, vivax and knowlesi malaria. Our findings provide further evidence of the importance of the OPG/RANKL/TRAIL pathway in pathogenesis of diseases involving systemic inflammation, and may have implications for adjunctive therapies. Further evaluation of the role of B cell production of OPG in host responses to malaria and other inflammatory diseases is warranted.

A Mathematical Model for Fibrous Dysplasia: The Role of the Flow of Mutant Cells

Fibrous dysplasia (FD) is a mosaic non-inheritable genetic disorder of the skeleton in which normal bone is replaced by structurally unsound fibro-osseous tissue. There is no curative treatment for FD, partly because its pathophysiology is not yet fully known. We present a simple mathematical model of the disease incorporating its basic known biology, to gain insight on the dynamics of the involved bone-cell populations, and shed light on its pathophysiology. We develop an analytical study of the model and study its basic properties. The existence and stability of steady states are studied, an analysis of sensitivity on the model parameters is done, and different numerical simulations provide findings in agreement with the analytical results. We discuss the model dynamics match with known facts on the disease, and how some open questions could be addressed using the model.

Osteoprotegerin Is Essential for the Development of Endothelial Dysfunction Induced by Angiotensin II in Mice

Opinions on the effects of osteoprotegerin (OPG) have evolved over the years from a protein protecting the vasculature from calcification to a cardiovascular risk factor contributing to inflammation within the vascular wall. Nowadays, the link between OPG and angiotensin II (Ang II) appears to be particularly important. In this study, the endothelial function was investigated in OPG-knockout mice (B6.129.S4-OPG, OPG-) and wild-type (C57BL/6J, OPG+) mice under basic conditions and after Ang II exposure by assessing the endothelium-dependent diastolic response of aortic rings to acetylcholine in vitro. A further aim of the study was to compare the effect of Ang II on the expression of cytokines in the aortic wall of both groups of mice. Our study shows that rings from OPG- mice had their normal endothelial function preserved after incubation with Ang II, whereas those from OPG+ mice showed significant endothelial dysfunction. We conclude that the absence of OPG, although associated with a pro-inflammatory cytokine profile in the vascular wall, simultaneously protects against Ang II-induced increases in pro-inflammatory cytokines in the murine vascular wall. Our study also demonstrates that the absence of OPG can result in a decrease in the concentration of pro-inflammatory cytokines in the vascular wall after Ang II exposure. The presence of OPG is therefore crucial for the development of Ang II-induced inflammation in the vascular wall and for the development of Ang II-induced endothelial dysfunction.

Osteoclasts at Bone Remodeling: Order from Order

Osteoclasts are multinucleated bone-resorbing cells derived from the monocyte/macrophage lineage. The macrophage colony-stimulating factor/receptor activator of nuclear factor κB ligand (M-CSF/RANKL) signaling network governs the differentiation of precursor cells into fusion-competent mononucleated cells. Repetitive fusion of fusion-competent cells produces multinucleated osteoclasts. Osteoclasts are believed to die via apoptosis after bone resorption. However, recent studies have found that osteoclastogenesis in vivo proceeds by replacing the old nucleus of existing osteoclasts with a single newly differentiated mononucleated cell. Thus, the formation of new osteoclasts is minimal. Furthermore, the sizes of osteoclasts can change via cell fusion and fission in response to external conditions. On the other hand, osteoclastogenesis in vitro involves various levels of heterogeneity, including osteoclast precursors, mode of fusion, and properties of the differentiated osteoclasts. To better understand the origin of these heterogeneities and the plasticity of osteoclasts, we examine several processes of osteoclastogenesis in this review. Candidate mechanisms that create heterogeneity involve asymmetric cell division, osteoclast niche, self-organization, and mode of fusion and fission. Elucidation of the plasticity or fluctuation of the M-CSF/RANKL network should be an important topic for future researches.

Histone methyltransferase SETDB1 promotes osteogenic differentiation in osteoporosis by activating OTX2-mediated BMP-Smad and Wnt/β-catenin pathways

Osteogenic differentiation plays important roles in the pathogenesis of osteoporosis. In this study, we explored the regulatory mechanism of histone methyltransferase SET domain bifurcated 1 (SETDB1) underlying the osteogenic differentiation in osteoporosis. The common osteoporosis-related genes were retrieved from the GeneCards, CTD, and Phenolyzer databases. The enrichment analysis was conducted on the candidate osteoporosis-related genes using the PANTHER software, and the binding site between transcription factors and target genes predicted by hTFtarget. The bioinformatics analyses suggested 6 osteoporosis-related chromatin/chromatin binding protein or regulatory proteins (HDAC4, SIRT1, SETDB1, MECP2, CHD7, and DKC1). Normal and osteoporosis tissues were collected from osteoporosis patients to examine the expression of SETDB1. It was found that SETDB1 was poorly expressed in osteoporotic femoral tissues, indicating that SETDB1 might be involved in the development of osteoporosis. We induced SETDB1 overexpression/knockdown, orthodenticle homeobox 2 (OTX2) overexpression, activation of Wnt/β-catenin or BMP-Smad pathways alone or in combination in osteoblasts or ovariectomized mice. The data indicated that SETDB1 methylation regulated H3K9me3 in the OTX2 promoter region and inhibited the expression of OTX2. Besides, the BMP-Smad and Wnt/β-catenin pathways were inhibited by OTX2, thereby resulting in inhibited osteogenic differentiation. Animal experiments showed that overexpressed SETDB1 could promote the increase of calcium level and differentiation of femoral tissues. In conclusion, upregulation of SETDB1 promotes osteogenic differentiation by inhibiting OTX2 and activating the BMP-Smad and Wnt/β-catenin pathways in osteoporosis.

Reactive Oxygen Species Control Osteoblast Apoptosis through SIRT1/PGC-1α/P53Lys382 Signaling, Mediating the Onset of Cd-Induced Osteoporosis

The imbalance between osteogenesis and osteoclastogenesis is a feature of bone metabolic disease. Cadmium (Cd) exposure causes human bone loss and osteoporosis (OP) through bioaccumulation of the food chain. However, the impact of Cd on bone tissues and the underlying molecular mechanisms are not well-characterized. In the current study, we found that the Cd concentration in bone tissues of OP patients was higher than normal subjects; meanwhile, the nuclear silent information regulator of transcription 1 (SIRT1) protein expression level was significantly decreased, which is a new star molecule to treat OP. It is further revealed that SIRT1 activation markedly reprograms bone metabolic and stress-response pathways that incline with osteoblast (OB) apoptosis. Suppressing reactive oxygen species (ROS) release with N-acetyl-l-cysteine (NAC) abolished Cd-induced reduction of SIRT1 protein, deacetylation of P53, OB apoptosis, and attenuated OP. Conversely, overexpression of SIRT1 suppressed Cd-induced ROS release. SIRT1 overexpression in vivo and in vitro dampened PGC-1α protein, acetylation of P53 at lysine 382, and caspase-dependent apoptosis. These results reveal that ROS/SIRT1 controls P53 acetylation and coordinates OB apoptosis involved in the onset of OP.

Inflammatory, Metabolic, and Coagulation Effects on Medial Arterial Calcification in Patients with Peripheral Arterial Disease

Calcium deposits in the vessel wall in the form of hydroxyapatite can accumulate in the intimal layer, as in atherosclerotic plaque, but also in the medial layer, as in medial arterial calcification (MAC) or medial Möenckeberg sclerosis. Once considered a passive, degenerative process, MAC has recently been shown to be an active process with a complex but tightly regulated pathophysiology. Atherosclerosis and MAC represent distinct clinical entities that correlate in different ways with conventional cardiovascular risk factors. As both entities coexist in the vast majority of patients, it is difficult to estimate the relative contribution of specific risk factors to their development. MAC is strongly associated with age, diabetes mellitus, and chronic kidney disease. Given the complexity of MAC pathophysiology, it is expected that a variety of different factors and signaling pathways may be involved in the development and progression of the disease. In this article, we focus on metabolic factors, primarily hyperphosphatemia and hyperglycemia, and a wide range of possible mechanisms by which they might contribute to the development and progression of MAC. In addition, we provide insight into possible mechanisms by which inflammatory and coagulation factors are involved in vascular calcification processes. A better understanding of the complexity of MAC and the mechanisms involved in its development is essential for the development of potential preventive and therapeutic strategies.

Associations between bone mineral density and subclinical peripheral arterial disease in elderly men with type 2 diabetes mellitus

The association between peripheral arterial disease (PAD) and osteoporosis in elderly men with type 2 diabetes mellitus (T2DM) remains unclear. We demonstrated the association between subclinical PAD and decreased total hip bone mineral density (BMD) in men aged ≥ 55 years with T2DM, providing clinical clues for the early detection of decreased bone density in total hip.

PURPOSE

To investigate the association between subclinical peripheral arterial disease (PAD) and bone mineral density (BMD) at total hip, femoral neck, and lumbar spine (L_1-4) in elderly men with type 2 diabetes mellitus (T2DM).

METHODS

We identified 2,466 patients with confirmed diabetes in this retrospective cross-sectional study. A total of 272 men aged ≥ 55 years with T2DM (50 with subclinical PAD and 222 without PAD) were analyzed. Partial correlation analysis was conducted to explore the associations between ankle-brachial index (ABI) and BMD. Multivariate logistic regression analysis was performed to analyze the contributor for low bone density (T-score <  - 1.0).

RESULTS

Patients with T2DM and subclinical PAD (ABI ≤ 0.9) had significantly lower total hip BMD and T-score (BMD, 0.87 ± 0.14 vs. 0.92 ± 0.15 g/cm², P = 0.014; T-score, -1.30 [-1.70 to -0.45] vs. -0.80 [-1.40 to 0.00], P = 0.009) than those in the control group. The partial correlation analyses indicated that ABI significantly correlated with the total hip T-score (adjusted r = 0.166, P = 0.009). The logistic regression analysis indicated that subclinical PAD was an independent risk factor for the risk of decreased bone density in total hip (adjusted odds ratio [95% CI]: 8.933 [1.075-74.222], P = 0.043).  CONCLUSION: Subclinical PAD (ABI ≤ 0.9) could be used as a risk factor for decreased total hip BMD in men aged ≥ 55 years with T2DM, which provides clinical clues for the early detection of low bone density in total hip in such populations.

Bone remodeling: an operational process ensuring survival and bone mechanical competence

Bone remodeling replaces old and damaged bone with new bone through a sequence of cellular events occurring on the same surface without any change in bone shape. It was initially thought that the basic multicellular unit (BMU) responsible for bone remodeling consists of osteoclasts and osteoblasts functioning through a hierarchical sequence of events organized into distinct stages. However, recent discoveries have indicated that all bone cells participate in BMU formation by interacting both simultaneously and at different differentiation stages with their progenitors, other cells, and bone matrix constituents. Therefore, bone remodeling is currently considered a physiological outcome of continuous cellular operational processes optimized to confer a survival advantage. Bone remodeling defines the primary activities that BMUs need to perform to renew successfully bone structural units. Hence, this review summarizes the current understanding of bone remodeling and future research directions with the aim of providing a clinically relevant biological background with which to identify targets for therapeutic strategies in osteoporosis.

The osteo-angiogenic signaling crosstalk for bone regeneration: harmony out of complexity

In recent years it has been increasingly appreciated that blood vessels are not simply suppliers of nutrients and oxygen, but actually play an exquisite regulatory role in bone development and repair. A specialized kind of endothelium, named type H because of its high expression of CD31 and Endomucin, constitutes anatomically defined vessels in proximity of the epiphyseal growth plate. Type H endothelium regulates the proliferation and differentiation of both osteoblasts and osteoclasts through the secretion of angiocrine signals and is a hub for the bidirectional molecular crosstalk between the different cell populations of the osteogenic microenvironment. Type H vessels are a key target for current translational approaches aiming at coupling angiogenesis and osteogenesis for bone repair. Open questions remain about their presence and features in notstereotyped tissues, like engineered osteogenic grafts, and the opportunities for their clinical stimulation by pharmacological treatments.

Delineating the role of osteoprotegerin as a marker of breast cancer risk among women with a BRCA1 mutation

Women with a pathogenic germline mutation in the BRCA1 gene face a very high lifetime risk of developing breast cancer, estimated at 72% by age 80. Prophylactic bilateral mastectomy is the only effective way to lower their risk; however, most women with a mutation opt for intensive screening with annual MRI and mammography. Given that the BRCA1 gene was identified over 20 years ago, there is a need to identify a novel non-surgical approach to hereditary breast cancer prevention. Here, we provide a review of the emerging preclinical and epidemiologic evidence implicating the dysregulation of progesterone-mediated receptor activator of nuclear factor κB (RANK) signaling in the pathogenesis of BRCA1-associated breast cancer. Experimental studies have demonstrated that RANK inhibition suppresses Brca1-mammary tumorigenesis, suggesting a potential target for prevention. Data from studies conducted among women with a BRCA1 mutation further support this pathway in BRCA1-associated breast cancer development. Progesterone-containing (but not estrogen-alone) hormone replacement therapy is associated with an increased risk of breast cancer in women with a BRCA1 mutation. Furthermore, BRCA1 mutation carriers have significantly lower levels of circulating osteoprotegerin (OPG), the decoy receptor for RANK-ligand (RANKL) and thus endogenous inhibitor of RANK signaling. OPG levels may be associated with the risk of disease, suggesting a role of this protein as a potential biomarker of breast cancer risk. This may improve upon current risk prediction models, stratifying women at the highest risk of developing the disease, and further identify those who may be targets for anti-RANKL chemoprevention. Collectively, the evidence supports therapeutic inhibition of the RANK pathway for the primary prevention of BRCA1-associated breast cancer, which may generate unique prevention strategies (without prophylactic surgery) and enhance quality of life.

RANKL Blockade Reduces Cachexia and Bone Loss Induced by Non-Metastatic Ovarian Cancer in Mice

Tumor- and bone-derived soluble factors have been proposed to participate in the alterations of skeletal muscle size and function in cachexia. We previously showed that mice bearing ovarian cancer (OvCa) exhibit cachexia associated with marked bone loss, whereas bone-targeting agents, such as bisphosphonates, are able to preserve muscle mass in animals exposed to anticancer drugs. De-identified CT images and plasma samples from female patients affected with OvCa were used for body composition assessment and quantification of circulating cross-linked C-telopeptide type I (CTX-I) and receptor activator of NF-kB ligand (RANKL), respectively. Female mice bearing ES-2 tumors were used to characterize cancer- and RANKL-associated effects on muscle and bone. Murine C2C12 and human HSMM myotube cultures were used to determine the OvCa- and RANKL-dependent effects on myofiber size. To the extent of isolating new regulators of bone and muscle in cachexia, here we demonstrate that subjects affected with OvCa display evidence of cachexia and increased bone turnover. Similarly, mice carrying OvCa present high RANKL levels. By using in vitro and in vivo experimental models, we found that elevated circulating RANKL is sufficient to cause skeletal muscle atrophy and bone resorption, whereas bone preservation by means of antiresorptive and anti-RANKL treatments concurrently benefit muscle mass and function in cancer cachexia. Altogether, our data contribute to identifying RANKL as a novel therapeutic target for the treatment of musculoskeletal complications associated with RANKL-expressing non-metastatic cancers. © 2021 American Society for Bone and Mineral Research (ASBMR).

Decreased level of soluble receptor activator of nuclear factor-κβ ligand (sRANKL) in overweight and obese children

INTRODUCTION

Childhood obesity contributes to the development of cardiovascular diseases. The molecular pathway - receptor activator of nuclear factor-κβ ligand (RANKL), its receptor RANK and osteoprotegerin (OPG) - takes part not only in bone metabolism but is also involved in the atherosclerosis process. RANKL stimulates osteogenic differentiation and calcification of vascular smooth cells. The associations between the OPG-sRANKL system and various cardiovascular risk factors were displayed. We aimed to evaluate the relationships between serum sRANKL (soluble RANKL) levels and the OPG/sRANKL ratio with cardiometabolic risk factors in overweight and obese children.

MATERIAL AND METHODS

The study included 70 children with overweight and obesity (mean age 13.0 ± 2.8) and 35 age-matched normal weight, healthy peers as a control group. In all patients, anthropometric measurements and laboratory tests were performed. Additionally, an oral glucose tolerance test (OGTT) was made only in overweight and obese children. Atherogenic and insulin resistance indices were calculated.

RESULTS

Overweight and obese children had lower sRANKL levels compared to the control group (median 276.95 vs 325.90, p=0.011), and consequently a higher OPG/sRANKL ratio (0.02 vs 0.01, p = 0.013). The studied children in the lowest quartile of sRANKL levels had higher body weight, Body Mass Index, waist circumference and increased glucose and insulin levels 60 minutes after OGTT and higher uric acid values compared to children in the highest quartile. In multivariable linear regression analysis sRANKL negatively correlated only with uric acid (β = - 0.508, p = 0.041). No association was found for the OPG/sRANKL ratio.

CONCLUSION

Excess fat mass seems to alter the OPG/RANKL ratio mainly by reducing serum sRANKL levels. The correlation between sRANKL and uric acid may suggest a contribution of the OPG-sRANKL system in the cardiometabolic process, but that observation should be confirmed in future studies.

New Insights to the Crosstalk between Vascular and Bone Tissue in Chronic Kidney Disease-Mineral and Bone Disorder

Vasculature plays a key role in bone development and the maintenance of bone tissue throughout life. The two organ systems are not only linked in normal physiology, but also in pathophysiological conditions. The chronic kidney disease–mineral and bone disorder (CKD-MBD) is still the most serious complication to CKD, resulting in increased morbidity and mortality. Current treatment therapies aimed at the phosphate retention and parathyroid hormone disturbances fail to reduce the high cardiovascular mortality in CKD patients, underlining the importance of other factors in the complex syndrome. This review will focus on vascular disease and its interplay with bone disorders in CKD. It will present the very late data showing a direct effect of vascular calcification on bone metabolism, indicating a vascular-bone tissue crosstalk in CKD. The calcified vasculature not only suffers from the systemic effects of CKD but seems to be an active player in the CKD-MBD syndrome impairing bone metabolism and might be a novel target for treatment and prevention.

Metabolism of Subchondral Bone Tissue in Posttraumatic Osteoarthrosis in Rats

In rats with modeled posttraumatic knee osteoarthrosis, negative changes in subchondral bone metabolism were revealed: a tendency to an increase in osteocalcin concentration, a decrease in sclerostin and osteoprotegerin levels, and a significant increase in FGF-23 concentration accompanied by a slight elevation of inorganic phosphorous and significant increase in total calcium levels in comparison with the corresponding parameters in intact controls. These findings demonstrate crucial importance of structural integrity of the subchondral bone, because its protection improves the results of reconstructive therapy for local cartilage defects.

An In Vitro and In Vivo Comparison of Osteogenic Differentiation of Human Mesenchymal Stromal/Stem Cells

The use of stem cells in regenerative medicine, including tissue engineering and transplantation, has generated a great deal of enthusiasm. Mesenchymal stromal/stem cells (MSCs) can be isolated from various tissues, most commonly, bone marrow but more recently adipose tissue, dental pulp, and Wharton's jelly, to name a few. MSCs display varying phenotypic profiles and osteogenic differentiating capacity depending and their site of origin. MSCs have been successfully differentiated into osteoblasts both in vitro an in vivo but discrepancies exist when the two are compared: what happens in vitro does not necessarily happen in vivo, and it is therefore important to understand why these differences occur. The osteogenic process is a complex network of transcription factors, stimulators, inhibitors, proteins, etc., and in vivo experiments are helpful in evaluating the various aspects of this osteogenic process without distractions and confounding variables. With that in mind, the results of in vitro experiments need to be carefully considered and interpreted with caution as they do not perfectly replicate the conditions found within living organisms. This is where in vivo experiments help us better understand interactions that might occur in the osteogenic process that cannot be replicated in vitro. Potentially, these differences could also be exploited to develop an optimal MSC cell therapeutic product that can be used for bone disorders. There are many bone disorders, most of which cause a great deal of discomfort. Clinically acceptable protocols could be developed in which MSCs are used to aid in bone regeneration providing relief for patients with chronic pain. The aim of this review is to examine the differences between studies conducted in vitro and in vivo with regard to the osteogenic process to better define the gaps in current osteogenic research. By better understanding osteogenic differentiation, we can better define treatment strategies for various bone disorders.

Osteoprotegerin and RANKL-RANK-OPG-TRAIL signalling axis in heart failure and other cardiovascular diseases

Osteoprotegerin (OPG) is a glycoprotein involved in the regulation of bone remodelling. OPG regulates osteoclast activity by blocking the interaction between the receptor activator of nuclear factor kappa B (RANK) and its ligand (RANKL). More and more studies confirm the relationship between OPG and cardiovascular diseases. Numerous studies have confirmed that a high plasma concentration of OPG and a low concentration of tumour necrosis factor–related apoptosis inducing ligand (TRAIL) together with a high OPG/TRAIL ratio are predictors of poor prognosis in patients with myocardial infarction. A high plasma OPG concentration and a high ratio of OPG/TRAIL in the acute myocardial infarction are a prognostic indicator of adverse left ventricular remodelling and of the development of heart failure. Ever more data indicates the participation of OPG in the regulation of the function of vascular endothelial cells and the initiation of the atherosclerotic process in the arteries. Additionally, it has been shown that TRAIL has a protective effect on blood vessels and exerts an anti-atherosclerotic effect. The mechanisms of action of both OPG and TRAIL within the cells of the vascular wall are complex and remain largely unclear. However, these mechanisms of action as well as their interaction in the local vascular environment are of great interest to researchers. This article presents the current state of knowledge on the mechanisms of action of OPG and TRAIL in the circulatory system and their role in cardiovascular diseases. Understanding these mechanisms may allow their use as a therapeutic target in cardiovascular diseases in the future.

Omega 3 fatty acids effect on the vascular calcification biomarkers fetuin A and osteoprotegerin in hemodialysis patients

Chronic renal failure patients on dialysis are at a high risk of death due to vascular calcification. This study aimed at investigating the effect of omega-3 fatty acids on the vascular calcification biomarkers fetuin-A and osteoprotegerin (OPG) in patients with chronic renal failure who are undergoing hemodialysis. This prospective, open-label, controlled, parallel study included 60 hemodialysis patients who were randomized to receive either omega-3 fatty acids capsule along with their standard care of treatment (omega-3 group) or their standard care of treatment only (control group). Serum levels of fetuin-A, OPG, calcium, phosphorus, hemoglobin, parathyroid hormone, blood urea nitrogen (BUN), albumin, serum creatinine (SCr), and serum triglycerides (TG) were measured at baseline and after six months of intervention and follow-up of both groups. Significantly increased levels of fetuin-A and OPG (p < 0.001) were observed in the omega-3 group six months after the intervention compared with the control group. Levels of TG, albumin, SCr, BUN, phosphorous, calcium, hemoglobin, and parathyroid hormone were not significantly different in the omega-3 group compared with the control group after six months of intervention. Our study concluded that omega-3 may have a clinically beneficial effect in decreasing cardiovascular events by increasing the levels of the protective vascular calcification inhibitors fetuin-A and osteoprotegerin in chronic renal failure patients who are undergoing hemodialysis.

RANKL immunisation inhibits prostate cancer metastasis by modulating EMT through a RANKL-dependent pathway

Prostate cancer (PCa) morbidity in the majority of patients is due to metastatic events, which are a clinical obstacle. Therefore, a better understanding of the mechanism underlying metastasis is imperative if we are to develop novel therapeutic strategies. Receptor activator of nuclear factor kappa-B (NF-κB) ligand (RANKL) regulates bone remodelling. Thus, agents that suppress RANKL signalling may be useful pharmacological treatments. Here, we used preclinical experimental models to investigate whether an inactive form of RANKL affects bone metastasis in RANKL-induced PCa. RANKL was associated with epithelial–mesenchymal transition (EMT) and expression of metastasis-related genes in PC3 cells. Therefore, we proposed a strategy to induce anti-cytokine antibodies using mutant RANKL as an immunogen. RANKL promoted migration and invasion of PC3 cells through EMT, and induced a significant increase in binding of β-catenin to TCF-4, an EMT-induced transcription factor in PCa cells, via mitogen-activated protein kinase and β-catenin/TCF-4 signalling. Thus, RANKL increased EMT and the metastatic properties of PC3 cells, suggesting a role as a therapeutic target to prevent PCa metastasis. Treatment with mutant RANKL reduced EMT and metastasis of PC3 PCa cells in an experimental metastasis model. Thus, mutant RANKL could serve as a potential vaccine to prevent and treat metastatic PCa.

Assessment of the Healing of Dental Implant Surgical Site Following Low-Level Laser Therapy Using Bioclinical Parameters: An Exploratory Study

The purpose of this study was to evaluate whether low-level laser therapy improves healing of the implant surgical site with clinical and biochemical parameters. Thirty patients with an edentulous space spanning a single tooth were selected. The patients were randomly allocated to 1 of 2 groups: control group and test group. The test group received laser energy at a power of 2 J/cm2 with a total of 4-6 J energy over each implant. Clinical parameters (implant stability quotient, probing index, modified sulcus bleeding index) and osteoprotegerin were assessed at baseline and follow-up intervals (2 weeks, 6 weeks, and 3 months). The test group showed significantly higher implant stability quotient than the control group at 2 weeks (57.93 ± 3.95 vs 35.67 ± 3.08; P < . 01) and 3 months (58.86 ± 3.75 vs 67.06 ± 3.78; P < . 01). A significant rise in osteoprotegerin levels of the test group (686.30 ± 125.36 pg/mL at baseline and 784.25 ± 108.30 pg/mL at 3 months; P < . 01) was seen contrary to significant decline in the control group (839.50 ± 249.08 pg/mL at baseline vs 415.30 ± 78.39 pg/mL at 3 months; P < . 01). Within the limitations of the study, the findings suggest that the healing of peri-implant hard and soft tissues may be enhanced with the use of low-level laser therapy as an explicit modality during the postoperative period.

Role of the RANK/RANKL/OPG and Wnt/β-Catenin Systems in CKD Bone and Cardiovascular Disorders

In the course of chronic kidney disease (CKD), alterations in the bone-vascular axis augment the risk of bone loss, fractures, vascular and soft tissue calcification, left ventricular hypertrophy, renal and myocardial fibrosis, which markedly increase morbidity and mortality rates. A major challenge to improve skeletal and cardiovascular outcomes in CKD patients requires a better understanding of the increasing complex interactions among the main modulators of the bone-vascular axis. Serum parathyroid hormone (PTH), phosphorus (P), calcium (Ca), fibroblast growth factor 23 (FGF23), calcidiol, calcitriol and Klotho are involved in this axis interact with RANK/RANKL/OPG system and the Wnt/β-catenin pathway. The RANK/RANKL/OPG system controls bone remodeling by inducing osteoblast synthesis of RANKL and downregulating OPG production and it is also implicated in vascular calcification. The complexity of this system has recently increased due the discovery of LGR4, a novel RANKL receptor involved in bone formation, but possibly also in vascular calcification. The Wnt/β-catenin pathway plays a key role in bone formation: when this pathway is activated, bone is formed, but when it is inhibited, bone formation is stopped. In the progression of CKD, a downregulation of the Wnt/β-catenin pathway has been described which occurs mainly through the not coincident elevations of sclerostin, Dickkopf1 (Dkk1) and the secreted Frizzled Related Proteins (sFRPs). This review analyzes the interactions of PTH, P, Ca, FGF23, calcidiol, calcitriol and Klotho with the RANKL/RANKL/OPG system and the Wnt/β-catenin, pathway and their implications in bone and cardiovascular disorders in CKD.

The miR-155-5p inhibits osteoclast differentiation through targeting CXCR2 in orthodontic root resorption

BACKGROUND AND OBJECTIVE

Root resorption is an unavoidable side effect of orthodontic tooth movement. The mechanism of root resorption is similar to bone resorption; the odontoclasts share similar characteristics with osteoclasts (OCs). MicroRNAs (miRNAs) such as miR-155-5p play an important role in OC differentiation, but the underlying molecular mechanism of miR-155-5p in this process is not fully understood. We found that the miR-155-5p seed sequences were complementary to a sequence conserved in the 3-untranslated region of CXCR2 mRNA. In this study, we explored the molecular mechanism underlying the effect of miR-155-5p on OC differentiation by targeting CXCR2.

MATERIALS AND METHODS

In this study, we divided the orthodontic patients into mild, moderate, and severe groups according to the severity of root resorption. The gingival crevicular fluid (GCF) of patients in different groups was collected, and the expression levels of dentin phosphoprotein (DPP) were detected by ELISA, and the expression levels of CXCR2 and miR-155-5p in GCF were detected by real-time quantitative PCR (qRT-PCR). The relationship between miR-155-5p and CXCR2 was verified by double luciferase. We analyzed changes of CXCR2 and miR-155-5p expression after transfection of miR-155-5p mimic and inhibitor into RAW264.7 cells induced by receptor activator of nuclear factor-κB ligand (RANKL) through qRT-PCR and western blotting. The effect of miR-155-5p on OC differentiation was evaluated by tartrate-resistant acid phosphatase (TRAP) staining. QRT-PCR and western blotting were used to analyze expression of the osteoclastic bone resorption-related enzymes carbonic anhydrase 2 (CA II), matrix metalloproteinase-9 (MMP-9), and cathepsin K. To further confirm the direct targeting effect of CXCR2 by miR-155-5p, we blocked CXCR2 using si-CXCR2 in RANKL-induced RAW264.7 cells.

RESULTS

Dentin phosphoprotein levels were consistent with the trend of miR-155-5p changes, and the trend of CXCR2 expression was opposite to miR-155-5p changes. miR-155-5p can be directly targeted to act on CXCR2. The expression of miR-155-5p was significantly downregulated in differentiated OCs. MiR-155-5p inhibited OC differentiation, and downregulated CA II, MMP-9, and cathepsin K expression at the protein and mRNA levels.

CONCLUSIONS

In summary, the results of this study suggested that miR-155-5p inhibited OC differentiation by targeting CXCR2, thus reducing root resorption in orthodontics. MiR-155-5p can be used as an effective target for avoiding or reducing the degree of root resorption in orthodontic treatment.

Skeleton-vasculature chain reaction: a novel insight into the mystery of homeostasis

Angiogenesis and osteogenesis are coupled. However, the cellular and molecular regulation of these processes remains to be further investigated. Both tissues have recently been recognized as endocrine organs, which has stimulated research interest in the screening and functional identification of novel paracrine factors from both tissues. This review aims to elaborate on the novelty and significance of endocrine regulatory loops between bone and the vasculature. In addition, research progress related to the bone vasculature, vessel-related skeletal diseases, pathological conditions, and angiogenesis-targeted therapeutic strategies are also summarized. With respect to future perspectives, new techniques such as single-cell sequencing, which can be used to show the cellular diversity and plasticity of both tissues, are facilitating progress in this field. Moreover, extracellular vesicle-mediated nuclear acid communication deserves further investigation. In conclusion, a deeper understanding of the cellular and molecular regulation of angiogenesis and osteogenesis coupling may offer an opportunity to identify new therapeutic targets.

Appraisal of the Antiarthritic Potential of Prazosin via Inhibition of Proinflammatory Cytokine TNF-α: A Key Player in Rheumatoid Arthritis

Prazosin, a selective α₁ adrenergic receptor antagonist, with documented anti-inflammatory potential, was evaluated for its antiarthritic efficacy by targeting specifically TNF-α. The antiarthritic attribute of prazosin validated through in vitro screening comprised thermally provoked denaturation of bovine serum albumin (BSA) and egg albumin along with membrane stabilization evaluation at a concentration of 100-6400 μg/mL, while in vivo screening comprised formaldehyde-instigated arthritis at the doses of 5, 10, and 20 mg/kg and complete Freund's adjuvant (CFA)-induced arthritis at 20 mg/kg dose. Paw swelling, body weight, arthritic score, hematological parameters, and histological and radiographic examination of ankle joints were assessed for a period of 28 days after CFA immunization. Moreover, the proinflammatory cytokine TNF-α level was also assessed through quantitative real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). Prazosin revealed significant antiarthritic effect evident through protein denaturation inhibition in the egg albumin and the BSA model, stabilization of red blood cell membrane in the membrane stabilizing assay, and reduction in paw volume in formaldehyde-induced arthritis. Likewise, prazosin exhibited propitious antiarthritic effects in the CFA-provoked arthritis model manifested by paw volume and arthritic score alleviation, substantial weight loss prevention, and preservation of the normal hematological and biochemical profile. Histological and X-ray investigation unveiled no substantive structural alterations in treated rat's ankle joints. The TNF-α expression level was also reduced. Thus, the current study is suggestive that prazosin exhibits a strong antiarthritic potential possibly through inhibition of TNF-α.

Insights into the mechanism of vascular endothelial cells on bone biology

In the skeletal system, blood vessels not only function as a conduit system for transporting gases, nutrients, metabolic waste, or cells but also provide multifunctional signal molecules regulating bone development, regeneration, and remodeling. Endothelial cells (ECs) in bone tissues, unlike in other organ tissues, are in direct contact with the pericytes of blood vessels, resulting in a closer connection with peripheral connective tissues. Close-contact ECs contribute to osteogenesis and osteoclastogenesis by secreting various cytokines in the paracrine or juxtacrine pathways. An increasing number of studies have revealed that extracellular vesicles (EVs) derived from ECs can directly regulate maturation process of osteoblasts and osteoclasts. The different pathways focus on targets at different distances, forming the basis of the intimate spatial and temporal link between bone tissue and blood vessels. Here, we provide a systematic review to elaborate on the function of ECs in bone biology and its underlying mechanisms based on three aspects: paracrine, EVs, and juxtacrine. This review proposes the possibility of a therapeutic strategy targeting blood vessels, as an adjuvant treatment for bone disorders.

Influence of the TGF-β Superfamily on Osteoclasts/Osteoblasts Balance in Physiological and Pathological Bone Conditions

The balance between bone forming cells (osteoblasts/osteocytes) and bone resorbing cells (osteoclasts) plays a crucial role in tissue homeostasis and bone repair. Several hormones, cytokines, and growth factors-in particular the members of the TGF-β superfamily such as the bone morphogenetic proteins-not only regulate the proliferation, differentiation, and functioning of these cells, but also coordinate the communication between them to ensure an appropriate response. Therefore, this review focuses on TGF-β superfamily and its influence on bone formation and repair, through the regulation of osteoclastogenesis, osteogenic differentiation of stem cells, and osteoblasts/osteoclasts balance. After introducing the main types of bone cells, their differentiation and cooperation during bone remodeling and fracture healing processes are discussed. Then, the TGF-β superfamily, its signaling via canonical and non-canonical pathways, as well as its regulation by Wnt/Notch or microRNAs are described and discussed. Its important role in bone homeostasis, repair, or disease is also highlighted. Finally, the clinical therapeutic uses of members of the TGF-β superfamily and their associated complications are debated.

Local Production of Osteoprotegerin by Osteoblasts Suppresses Bone Resorption

Osteoprotegerin (OPG) inhibits the ability of receptor activator of nuclear factor κB (NF-κB) ligand (RANKL) to stimulate the differentiation, activity, and survival of bone-resorbing osteoclasts. Genetic studies in mice show that osteocytes are an important source of RANKL, but the cellular sources of OPG are unclear. We use conditional deletion of Tnfrsf11b, which encodes OPG, from different cell populations to identify functionally relevant sources of OPG in mice. Deletion from B lymphocytes and osteocytes, two cell types commonly thought to supply OPG, has little or no impact on bone mass. By contrast, deletion of Tnfrsf11b from osteoblasts increases bone resorption and reduces bone mass to an extent similar to germline deletion, demonstrating that osteoblasts are an essential source of OPG. These results suggest that, in addition to producing new bone matrix, osteoblasts also play an active role in terminating the resorption phase of the bone remodeling cycle by suppressing RANKL activity.

Metformin, resveratrol, and exendin-4 inhibit high phosphate-induced vascular calcification via AMPK-RANKL signaling

Vascular calcification increases the risk of developing cardiovascular disease, and it is closely associated with metabolic disorders such as diabetes mellitus and non-alcoholic fatty liver disease. We investigated whether the activators of AMP-activated protein kinase (AMPK), metformin, resveratrol, and exendin-4, improved inorganic phosphate (Pi)-induced vascular calcification in rat vascular smooth muscle cells (VSMCs) and whether these effects were via AMPK. Pi increased calcium deposition in a dose-dependent manner, and metformin, resveratrol, and exendin-4 significantly decreased calcium deposition in the Pi-treated VSMCs. Moreover, metformin and exendin-4 increased the expression of a SMC marker gene, α-smooth muscle actin, and Ampk and reduced the receptor activator of nuclear factor kappa-Β ligand (Rankl)/osteoprotegerin ratio. Metformin, resveratrol, and exendin-4 reduced the expression of osteoblast differentiation-associated factors, such as runt-related transcription factor 2, bone morphogenic protein-2, p-small mothers against decapentaplegic 1/5/8, and Rankl. Inhibition of AMPK by siRNA adversely affected the anti-calcification effects of metformin, resveratrol, and exendin-4 and reversed the reduction of the expression of Rankl by metformin and exendin-4 in the Pi-treated VSMCs. These data suggest that metformin, resveratrol, and exendin-4 ameliorate Pi-induced vascular calcification by inhibiting osteoblast differentiation of VSMCs, which is mediated by AMPK.

Osteoclast formation at the bone marrow/bone surface interface: Importance of structural elements, matrix, and intercellular communication

Osteoclasts, the multinucleated cells responsible for bone resorption, have an enormous destructive power which demands to be kept under tight control. Accordingly, the identification of molecular signals directing osteoclastogenesis and switching on their resorptive activity have received much attention. Mandatory factors were identified, but a very essential aspect of the control mechanism of osteoclastic resorption, i.e. its spatial control, remains poorly understood. Under physiological conditions, multinucleated osteoclasts are only detected on the bone surface, while their mono-nucleated precursors are only in the bone marrow. How are pre-osteoclasts targeted to the bone surface? How is their progressive differentiation coordinated with their approach to the bone surface sites to be resorbed, which is where they finally fuse? Here we review the information on the bone marrow distribution of differentiating pre-osteoclasts relative to the position of the mandatory factors for their differentiation as well as relative to physical entities that may affect their access to the remodelling sites. This info allows recognizing an "osteoclastogenesis route" through the bone marrow and leading to the coincident fusion/resorption site - but also points to what still remains to be clarified regarding this route and regarding the restriction of fusion at the resorption site. Finally, we discuss the mechanism responsible for the start of resorption and its spatial extension. This review underscores that fully understanding the control of bone resorption requires to consider it in both space and time - which demands taking into account the context of bone tissue.

The Impact of Hyperbaric Oxygen Therapy on Serum C-Reactive Protein Levels, Osteoprotegerin Expression, and Osteoclast Numbers in Induced-Periodontitis Diabetic Rats

Objectives  This study aimed to examine the impact of hyperbaric oxygen therapy (HBOT) on serum C-reactive protein (CRP) levels, osteoclast numbers, and osteoprotegerin (OPG) expression in periodontitis-induced diabetic rats

Materials and Methods  This study constituted an in vivo laboratory-based experiment incorporating a posttest only control group design. Thirty male Wistar rats were divided into three groups of research subjects: a healthy group (K0), periodontitis-induced diabetic group (K1), and periodontitis-induced diabetic group treated with HBOT for 7 days (K2). After treatment, the subjects were sacrificed to determine the level of serum CRP by the ELISA method. Immunohistochemical analysis was conducted to check the level of OPG expression, while a histological analysis was undertaken to quantify the number of osteoclasts.

Statistical Analysis  The data was analyzed using a one-way ANOVA and Least Significant Difference (LSD) test on which a result of p < 0.05 was considered statistically significant.

Results  HBOT appreciably decreased serum CRP levels, significantly enhancing OPG expression in periodontitis-induced diabetic ( p < 0.05) and decreasing the number of osteoclasts in -periodontitis-induced diabetic ( p > 0.05).

Conclusion  HBOT reduced the serum CRP level, increased OPG expression, and decreased osteoclast numbers in periodontitis-induced diabetic rats.

LPS-induced inflammation disorders bone modeling and remodeling by inhibiting angiogenesis and disordering osteogenesis in chickens

Inflammation plays a negative role in the growth and development of bone. However, the underlining mechanisms of inflammation caused abnormal bone development and even bone disease are still poorly understood, especially in chickens. In this study, we explored the influence of inflammation on bone formation in broilers for the first time by using lipopolysaccharide (LPS) to establish systemic inflammatory models in chickens with tibia as the research object. The measurements of production and tibial parameters showed an inefficient production performance and lower growth rate in LPS group. We also found a large amount of platelets, inflammatory cells in chickens' blood and higher levels of inflammatory factors in serum after LPS injection, meanwhile, increase in thrombus, chondrocyte nucleolysis, and osteoclasts and a reduction in blood vessels were observed in growth plate through histological observation. The qPCR analysis showed that the mRNA expression levels of NF-κB, TLR4, TF, TPO, and its receptor C-MPL enhanced, while VEGFA was inhibited in LPS group. In addition, in OPG/RANKL system, OPG was decreased while RANKL enhanced. It was also observed that the mRNA levels of MMP-9 and its inducing factor CD147 enhanced in LPS group. The western blot results were basically in consistent with mRNA test. Thus, we infer that inflammation can inhibit bone modeling and remodeling by affecting angiogenesis and osteogenesis, and result in negative effect on bone formation furtherly.

Glyburide inhibits the bone resorption induced by traumatic occlusion in rats

OBJECTIVE

To examine whether glyburide inhibits bone destruction caused by traumatic occlusion in a rat occlusal trauma model.

BACKGROUND

Excessive mechanical stress, such as traumatic occlusion, induces expression of IL-1β and may be involved in bone resorption. NLRP3 inflammasomes have been linked to IL-1β expression, but it is currently unclear whether glyburide, the inhibiter of NLRP3 inflammasome, suppresses occlusal trauma in rats.

METHODS

Male SD rats aged 7 weeks were used. In the trauma group, the occlusal surface of the maxillary first right molar was raised by attaching a metal wire to apply occlusal trauma to the mandibular first right molar. In the trauma + glyburide group, the NLRP3 inhibitor glyburide was administered orally every 24 hours from 1 day before induction of occlusal trauma. Rats were euthanized after 5 or 10 days, and the maxillary first molars were harvested with the adjacent tissues for histopathological investigation. Immunohistochemical expression of IL-1β, NLRP3, and RANKL was also assessed.

RESULTS

On day 5, bone resorption was significantly greater in the trauma group compared with the control group or the trauma + glyburide group, and there were significantly higher numbers of osteoclasts and cells positive for IL-1β, NLRP3, and RANKL in the trauma group.

CONCLUSION

In this study, glyburide inhibits bone resorption by traumatic occlusion in rats. It suggests that the NLRP3/IL-1β pathway might be associated with bone resorption induced by traumatic occlusion.

Osteoprotegerin in diabetic osteopathy

AIM

The aim of this study is to evaluate the relationship between OPG and the degree of glycaemic control in a population of elderly subjects.

METHODS AND RESULTS

Data presented included 172 elderly subjects, of whom 107 were hospitalized for a hip fracture and 65 were non fractured outpatients. All participants received a multidimensional geriatric evaluation and underwent blood sampling. HbA1c, OPG, CTX and OC were measured and DXA scans were performed. Carotid intima-media thickness (IMT) was measured in all outpatients. Diabetic patients had more comorbidities, higher mean values of lumbar spine and femoral neck BMD and T-score, lower circulating levels of OC and CTX, and higher circulating levels of OPG compared to non-diabetic subjects. OPG was directly correlated with HbA1c. This association was most evident in non-fractured elderly subjects. Moreover, diabetic patients with IMT>1.5 mm had greater mean values of OPG than non-diabetic subjects with high IMT and than elderly subjects with IMT < 1.5 mm, with and without T2DM.

CONCLUSIONS

Diabetic patients have reduced circulating levels of OC and CTX, and elevated serum levels of OPG, suggesting a state of low bone turnover. Reduced bone turnover causes an increase of BMD and could lead to a poor bone quality. OPG and HbA1c were directly correlated and OPG mean values were higher in diabetic patients with poor glucose control. Diabetic osteopathy could be considered a late complication of T2DM, directly related with the degree of glucose control and the duration of the disease.

Stromal cell-derived factor-1 (CXCL12) and its role in bone and muscle biology

Musculoskeletal disorders are the leading cause of disability worldwide; two of the most prevalent of which are osteoporosis and sarcopenia. Each affect millions in the aging population across the world and the associated morbidity and mortality contributes to billions of dollars in annual healthcare cost. Thus, it is important to better understand the underlying pathologic mechanisms of the disease process. Regulatory chemokine, CXCL12, and its receptor, CXCR4, are recognized to be essential in the recruitment, localization, maintenance, development and differentiation of progenitor stem cells of the musculoskeletal system. CXCL12 signaling results in the development and functional ability of osteoblasts, osteoclasts, satellite cells and myoblasts critical to maintaining musculoskeletal homeostasis. Interestingly, one suggested pathologic mechanism of osteoporosis and sarcopenia is a decline in the regenerative capacity of musculoskeletal progenitor stem cells. Thus, because CXCL12 is critical to progenitor function, a disruption in the CXCL12 signaling axis might play a distinct role in these pathological processes. Therefore, in this article, we perform a review of CXCL12, its physiologic and pathologic function in bone and muscle, and potential targets for therapeutic development.

Reproductive and Lifestyle Factors and Circulating sRANKL and OPG Concentrations in Women: Results from the EPIC Cohort

BACKGROUND

Except for a documented increase in osteoprotegerin (OPG) concentrations with older age, data on determinants of soluble Receptor Activator of Nuclear Factor κB (sRANKL) and OPG concentrations in women are limited. We evaluated reproductive and lifestyle factors as potential sources of variation in circulating sRANKL and OPG concentrations in pre- and postmenopausal women.

METHODS

This study includes 2,016 controls [n = 1,552 (76%) postmenopausal, n = 757 (38%) using postmenopausal hormone therapy (PMH)] from a breast cancer case-control study nested in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. Serum sRANKL was measured using an ELISA and serum OPG using an electrochemiluminescent assay. Generalized linear models were used to evaluate associations between these analytes and reproductive and lifestyle factors.

RESULTS

Older age at blood collection was associated with lower sRANKL concentrations in postmenopausal women (P trend ≤ 0.03) and higher OPG concentrations in all women (P trend ≤ 0.01). Longer duration of oral contraceptive use among premenopausal women and postmenopausal PMH users was associated with higher OPG (P trend ≤ 0.04). In postmenopausal non-PMH users, sRANKL concentrations were lower with longer duration of oral contraceptive use and current (vs. never) smoking (P ≤ 0.01). sRANKL concentrations were higher among women with higher BMI (P trend ≤ 0.01). The evaluated factors accounted for 12% of the variation in sRANKL concentrations and 21% of the variation in OPG concentrations.

CONCLUSIONS

Circulating sRANKL and OPG concentrations are minimally impacted by hormone-related factors in pre- and postmenopausal women.

IMPACT

This study suggests circulating concentrations of sRANKL and OPG are unlikely to be strongly modified by hormone-related reproductive and lifestyle factors.

Correlation between frontal sinus dimensions and cephalometric indices: A cross-sectional study

Objective:

Growth prediction plays a significant role in accurate diagnosis and treatment planning of orthodontics patients. It was hypothesized that the unique pattern of pneumatization of the frontal sinus as a component of craniofacial structure would influence the skeletal growth pattern and may be used as a growth predictor.

Materials and Methods:

A total of 144 subjects (78 females and 66 males) with a mean age of 19.26 ± 4.66 years were included in this retrospective study. Posterior-anterior and lateral cephalograms (LCs) were used to measure the frontal sinus dimensions. The skeletal growth pattern and relations of craniofacial structures were analyzed on LC using variables for sagittal and vertical analyses. Correlation between the frontal sinus dimensions and cephalometric indices was assessed by the Pearson's correlation coefficient.

Results:

The SN-FH and SNA angles had significant associations with frontal sinus dimensions in all enrolled subjects (P < 0.05). In males, the SN-FH, sum of posterior angles, Pal-SN, and Jarabak index were significantly associated with the size of frontal sinus (P < 0.05). In females, the associations of SN-FH and gonial angles with frontal sinus dimensions were significant (P < 0.05).

Conclusion:

The results show that larger size of frontal sinus was associated with reduced inclination of the anterior cranial base, increased anterior facial height (in males), and increased gonial angle (in females) in the study population.

Serum RANKL, osteoprotegerin (OPG) and RANKL/OPG ratio in children with systemic lupus erythematosus

Background

Systemic lupus erythematosus (SLE) patients have lower bone mineral density (BMD) compared with healthy individuals because of general, genetic, disease and medication-related factors. The disturbance of the receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG) ratio has been reported to be associated with low BMD in many disorders in adults and children alike.

Objectives

The objectives of this study were (i) to assess serum OPG, RANKL and RANKL/OPG ratio levels in SLE children and controls, (ii) to determine whether the cumulative glucocorticoid (CGCS) dose had any effect on the concentration of serum RANKL, OPG and RANKL/OPG ratio, and (iii) to determine the relation of these parameters to BMD.

Methods

We evaluated 50 SLE children and 50 age- and sex-matched healthy controls. RANKL and OPG were assessed in serum and compared between patients and controls. For SLE patients, a univariate followed by multivariable analysis were carried out to detect the possible predictors of the changes in RANKL, OPG and RANKL/OPG ratio levels. Lumbar BMD for all patients was assessed by dual-energy X-ray absorptiometry (DXA) scan and then correlated to different probable correlated factors.

Results

RANKL, OPG and RANKL/OPG ratio were significantly higher in SLE patients ( p ≤ 0.001). Univariate analysis showed significant correlations of RANKL with CGCS ( p ≤ 0.001) and with DXA scan z-score ( p = 0.007): OPG was significantly correlated to Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score ( p = 0.001) and anti-double-stranded DNA ( p = 0.001), whereas RANKL/OPG was significantly correlated to duration of illness and DXA z-score ( p = 0.002). The multivariable analysis showed that DXA z-score was an independent predictor of RANKL and RANKL/OPG ratio ( p = 0.019 and 0.008, respectively), whereas SLEDAI score was an independent predictor of OPG levels. BMD was negatively correlated to disease duration ( p = 0.008) and CGCS dose ( p = 0.015), but no significant correlation has been found between BMD and cumulative SLEDAI score ( p = 0.29).

Conclusions

Serum RANKL/OPG ratio is elevated in Egyptian children with SLE and is considered a risk factor for reduced bone mass in these children. Other risk factors for low BMD include high CGCS dose and disease duration, supporting that osteoporosis in SLE is multifactorial.

In vitro Models of Bone Remodelling and Associated Disorders

Disruption of bone remodelling by diseases such as osteoporosis results in an imbalance between bone formation by osteoblasts and resorption by osteoclasts. Research into these metabolic bone disorders is primarily performed in vivo; however, in the last decade there has been increased interest in generating in vitro models that can reduce or replace our reliance on animal testing. With recent advances in biomaterials and tissue engineering the feasibility of laboratory-based alternatives is growing; however, to date there are no established in vitro models of bone remodelling. In vivo, remodelling is performed by organised packets of osteoblasts and osteoclasts called bone multicellular units (BMUs). The key determinant of whether osteoclasts form and remodelling occurs is the ratio between RANKL, a cytokine which stimulates osteoclastogenesis, and OPG, its inhibitor. This review initially details the different circumstances, conditions, and factors which have been found to modulate the RANKL:OPG ratio, and fundamental factors to be considered if a robust in vitro model is to be developed. Following this, an examination of what has been achieved thus far in replicating remodelling in vitro using three-dimensional co-cultures is performed, before overviewing how such systems are already being utilised in the study of associated diseases, such as metastatic cancer and dental disorders. Finally, a discussion of the most important considerations to be incorporated going forward is presented. This details the need for the use of cells capable of endogenously producing the required cytokines, application of mechanical stimulation, and the presence of appropriate hormones in order to produce a robust model of bone remodelling.

Effects of RANKL Knockdown by Virus-like Particle-Mediated RNAi in a Rat Model of Osteoporosis

Rebalancing of the RANKL/OPG system seems to be an effective treatment strategy in postmenopausal osteoporosis. Here, we evaluate the knockdown of RANKL by in-vivo-delivered siRNA in a rat model of osteoporosis. Virus-like-particles (VLPs) derived from polyoma JC virus were used for delivering RANKL siRNA in ovariectomized (OVX) rats. 48 rats were ovariectomized and treated with either 17β-estradiol (E2), VLPs containing RANKL siRNA (siRANKL), or VLPs containing non-cognate siRNA (siCtrl). All OVX groups were subdivided into the prophylaxis group (PG) and the therapy group (TG). The PG received treatment directly after being OVX for 10 weeks. The TG received treatment 5 weeks after being OVX for 5 weeks. Rats were sacrificed 10 weeks after being OVX. Bone and blood samples were analyzed. E2 and siRANKL showed a significant knockdown of RANKL mRNA. A protein knockdown was observed with E2 and siRANKL in the TG but not in the PG. No distinct improvements in biomechanical and morphological properties of the bones were observed after siRANKL treatment. In the PG, E2 protected the bone structure. We demonstrated successful mRNA and protein knockdown by VLP-mediated RNAi in vivo. Knockdown of membranous RANKL did not result in significant improvements of bone properties in this model of early-stage postmenopausal osteoporosis.

Intravascular haemolysis in severe Plasmodium knowlesi malaria: association with endothelial activation, microvascular dysfunction, and acute kidney injury

Plasmodium knowlesi occurs throughout Southeast Asia, and is the most common cause of human malaria in Malaysia. Severe disease in humans is characterised by high parasite biomass, reduced red blood cell deformability, endothelial activation and microvascular dysfunction. However, the roles of intravascular haemolysis and nitric oxide (NO)-dependent endothelial dysfunction, important features of severe falciparum malaria, have not been evaluated, nor their role in acute kidney injury (AKI). In hospitalised Malaysian adults with severe (n = 48) and non-severe (n = 154) knowlesi malaria, and in healthy controls (n = 50), we measured cell-free haemoglobin (CFHb) and assessed associations with the endothelial Weibel–Palade body (WPB) constituents, angiopoietin-2 and osteoprotegerin, endothelial and microvascular function, and other markers of disease severity. CFHb was increased in knowlesi malaria in proportion to disease severity, and to a greater extent than previously reported in severe falciparum malaria patients from the same study cohort. In knowlesi malaria, CFHb was associated with parasitaemia, and independently associated with angiopoietin-2 and osteoprotegerin. As with angiopoietin-2, osteoprotegerin was increased in proportion to disease severity, and independently associated with severity markers including creatinine, lactate, interleukin-6, endothelial cell adhesion molecules ICAM-1 and E-selectin, and impaired microvascular reactivity. Osteoprotegerin was also independently associated with NO-dependent endothelial dysfunction. AKI was found in 88% of those with severe knowlesi malaria. Angiopoietin-2 and osteoprotegerin were both independent risk factors for acute kidney injury. Our findings suggest that haemolysis-mediated endothelial activation and release of WPB constituents is likely a key contributor to end-organ dysfunction, including AKI, in severe knowlesi malaria.

The Role of Osteoprotegerin as a Cardioprotective Versus Reactive Inflammatory Marker: the Chicken or the Egg Paradox

Cardiovascular disease is one of the most frequent causes of mortality and morbidity worldwide. Several variables have been identified as risk factors for cardiovascular disease. Recently, the role of receptor activator of nuclear factor kappa B, receptor activator of nuclear factor kappa B ligand, and the osteoprotegerin system has been recognized as more important in the pathogenesis of cardiovascular disease. Besides their roles in the regulation of bone resorption, these molecules have been reported to be associated with the pathophysiology of cardiovascular disease. There are conflicting data regarding the impact of osteoprotegerin, a glycoprotein with a regulatory role in the cardiovascular system. The aim of this review is to discuss the current knowledge and the role of osteoprotegerin in cardiovascular disease.

RANKL Inhibits the Production of Osteoprotegerin from Smooth Muscle Cells under Basal Conditions and following Exposure to Cyclic Strain

Receptor activator of nuclear factor-κB ligand (RANKL) promotes vascular calcification, while osteoprotegerin (OPG) opposes it by blocking RANKL activity. It remains unclear which vascular cell populations produce and secrete OPG/RANKL. This study characterizes the production of OPG/RANKL from human aortic endothelial and smooth muscle cells (HAECs and HASMCs) under various conditions. HAECs and HASMCs were exposed to inflammatory stimuli (tumor necrosis factor-α or hyperglycemia) or physiological levels of hemodynamic (cyclic) strain. After 72 h, both cells and supernatant media were harvested for assessment of OPG/RANKL production. Based on initial findings, the experiments involving HASMCs were then repeated in the presence of exogenous RANKL. OPG was produced and secreted by HASMCs and (to a considerably lesser degree) HAECs under basal conditions. Inflammatory stimuli upregulated OPG production in both cell populations. Cyclic strain significantly upregulated OPG production in HASMCs. Neither cell population produced RANKL. Exposing HASMCs to exogenous RANKL inhibited basal OPG production and completely abrogated the strain-mediated upregulation of OPG. These data suggest that HASMCs are a significant source of OPG within the vasculature but that RANKL, once present, downregulates this production and appears capable of preventing the "protective" upregulation of OPG seen with HASMCs exposed to physiological levels of cyclic strain.

Coordination of early cellular reactions during activation of bone resorption in the rat mandible periosteum: An immunohistochemical study

The activation step of bone remodeling remains poorly characterized. Activation comprises determination of the site to be remodeled, osteoclast precursor recruitment, their migration to the site of remodeling, and differentiation. These actions involve different compartments and cell types. The aim of this study was to investigate events and cell types involved during activation. We used a bone remodeling model in rats where extractions of the upper jaw molars initiate remodeling of the antagonist lower jaw (mandible) cortex along the periosteum. In this model osteoclastic resorption peaks 4 days after extractions. We previously reported that mast cell activation in the periosteum fibrous compartment is an early event of activation, associated with recruitment of circulating monocyte osteoclast precursors. By using immunohistochemistry, we observed 9 hours after induction a spatially oriented expression of InterCellular Adhesion Molecule-1 in the vessels that was inhibited by antagonists of histamine receptors 1 and 2. It was followed at 12 hours by the recruitment of ED1+ monocytes. In parallel, at 9 hours, Vascular Cellular Adhesion Molecule-1+ fibroblast-like cells scattered in the fibrous compartment of the periosteum between the vessels and the osteogenic compartment increased; these cells may be implicated in osteoclast precursor migration. Receptor Activator of NF KappaB Ligand+ cells increased at 12 hours in the osteogenic compartment and reached a peak at 18 hours. At 24 hours the numbers of osteogenic cells and subjacent osteocytes expressing semaphorin 3a, a repulsive for osteoclast precursors, decreased before returning to baseline at 48 hours. These data show that during activation the two periosteum compartments and several cell types are coordinated to recruit and guide osteoclast precursors towards the bone surface.

Unbalanced Vitreous Levels of Osteoprotegerin, RANKL, RANK, and TRAIL in Proliferative Diabetic Retinopathy

PURPOSE

We investigated the expression of the proinflammatory and proangiogenic factor osteoprotegerin (OPG) and its ligands, receptor activator of nuclear factor-κB ligand (RANKL), tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), and the receptor RANK in proliferative diabetic retinopathy (PDR).

MATERIALS AND METHODS

Vitreous samples from PDR and nondiabetic control patients and epiretinal membranes from PDR patients were studied by enzyme-linked immunosorbent assay, immunohistochemistry, and Western blot analysis.

RESULTS

Vascular endothelial growth factor, OPG, and soluble RANK levels in vitreous samples from PDR patients were significantly higher than that in nondiabetic controls. Soluble TRAIL levels were significantly lower in PDR patients than that in nondiabetic control, whereas soluble RANKL levels did not differ significantly. RANKL, RANK, and TRAIL were expressed in vascular endothelial cells, myofibroblasts, and CD45-expressing leukocytes in PDR epiretinal membranes.

CONCLUSIONS

Dysregulated expression of OPG/RANKL/RANK pathway and TRAIL might be related to inflammation and angiogenesis in PDR.

The role of 5-lipoxygenase in Aggregatibacter actinomycetemcomitans-induced alveolar bone loss

AIM

Leukotrienes (LTs) are pro-inflammatory lipid mediators formed by the enzyme 5-lipoxygenase (5-LO). The involvement of 5-LO metabolites in periodontal disease (PD) is not well defined. This study aimed to assess the role of 5-LO in experimental PD induced by Aggregatibacter actinomycetemcomitans (Aa).

MATERIAL AND METHODS

In vivo experiments were carried out using SV129 wild-type (WT) and 5-LO-deficient (5lo^-/- ) mice inoculated with Aa. Osteoclasts were stimulated in vitro with AaLPS in the presence or not of selective inhibitors of the 5-LO pathway, or LTB4 or platelet-activating factor (PAF), as PAF has already been shown to increase osteoclast activity.

RESULTS

In 5lo^-/- mice, there were no loss of alveolar bone and less TRAP-positive osteoclasts in periodontal tissues, after Aa inoculation, despite local production of TNF-α and IL-6. The differentiation and activity of osteoclasts stimulated with AaLPS were diminished in the presence of BLT1 antagonist or 5-LO inhibitor, but not in the presence of cysteinyl leukotriene receptor antagonist. The osteoclast differentiation induced by PAF was impaired by the BLT1 antagonism.

CONCLUSION

In conclusion, LTB4 but not CysLTs is important for Aa-induced alveolar bone loss. Overall, LTB4 affects osteoclast differentiation and activity and is a key intermediate of PAF-induced osteoclastogenesis.

The role of stromal cells in inflammatory bone loss

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation, local and systemic bone loss and a lack of compensatory bone repair. Fibroblast-like synoviocytes (FLS) are the most abundant cells of the stroma and a key population in autoimmune diseases such as RA. An increasing body of evidence suggests that these cells play not only an important role in chronic inflammation and synovial hyperplasia, but also impact bone remodelling. Under inflammatory conditions FLS release inflammatory cytokines, regulate bone destruction and formation and communicate with immune cells to control bone homeostasis. Other stromal cells, such as osteoblasts and terminally differentiated osteoblasts, termed osteocytes, are also involved in the regulation of bone homeostasis and are dysregulated during inflammation. This review highlights our current understanding of how stromal cells influence the balance between bone formation and bone destruction. Increasing our understanding of these processes is critical to enable the development of novel therapeutic strategies with which to treat bone loss in RA.

Matrix Metalloproteinases in Bone Resorption, Remodeling, and Repair

Matrix metalloproteinases (MMPs) are the major protease family responsible for the cleavage of the matrisome (global composition of the extracellular matrix (ECM) proteome) and proteins unrelated to the ECM, generating bioactive molecules. These proteins drive ECM remodeling, in association with tissue-specific and cell-anchored inhibitors (TIMPs and RECK, respectively). In the bone, the ECM mediates cell adhesion, mechanotransduction, nucleation of mineralization, and the immobilization of growth factors to protect them from damage or degradation. Since the first description of an MMP in bone tissue, many other MMPs have been identified, as well as their inhibitors. Numerous functions have been assigned to these proteins, including osteoblast/osteocyte differentiation, bone formation, solubilization of the osteoid during bone resorption, osteoclast recruitment and migration, and as a coupling factor in bone remodeling under physiological conditions. In turn, a number of pathologies, associated with imbalanced bone remodeling, arise mainly from MMP overexpression and abnormalities of the ECM, leading to bone osteolysis or bone formation. In this review, we will discuss the functions of MMPs and their inhibitors in bone cells, during bone remodeling, pathological bone resorption (osteoporosis and bone metastasis), bone repair/regeneration, and emergent roles in bone bioengineering.