Wnt but not BMP signaling is involved in the inhibitory action of sclerostin on BMP-stimulated bone formation

Mechanical Analysis of Romosozumab's Effects on Bone Strength in a Rat Posterolateral Lumbar Fusion Model

PURPOSE

 This study aimed to evaluate the effects of romosozumab, a humanized monoclonal antibody, on bone healing and mechanical strength in a rat posterolateral lumbar fusion (PLF) model. The primary objective was to determine its potential in promoting bone union and enhancing the structural integrity of graft sites, addressing challenges such as pseudarthrosis and hardware failure in spinal surgeries. These complications are particularly common in osteoporotic patients, where compromised bone quality and reduced healing capacity significantly increase the risk of surgical failure. With an aging global population, osteoporosis-related complications in spinal surgery are expected to rise, necessitating novel interventions to improve outcomes.

MATERIALS AND METHODS

 Twenty male Sprague-Dawley rats were randomized into two groups: romosozumab-treated (R) and control (C). All animals underwent bilateral PLF surgery involving the placement of autogenous bone grafts harvested from the spinous process combined with a demineralized bone matrix between the transverse processes of the lumbar vertebrae. Subcutaneous injections of romosozumab (105 mg/1.17 mL) or saline were administered twice weekly for 10 weeks. Bone healing was assessed through micro-computed tomography (CT) imaging at baseline and 10 weeks post-surgery. Key metrics included the bone fusion rate, fused bone volume, and bone mineral density (BMD). Additionally, the mechanical strength of the fusion mass was evaluated using a three-point bending test to determine the force required to induce rupture.

RESULTS

 The R group exhibited significant improvements across all evaluated parameters compared to the C group. Fused bone volume in the R group was significantly greater at 10 weeks (826.7 ± 27.5 mm³) compared to the C group (652.6 ± 30.7 mm³, p < 0.05), reflecting a higher bone volume growth rate (158.1 ± 12.9% vs. 106.8 ± 10.4%, p < 0.05). BMD at the distal femoral diaphysis was also markedly increased in the R group (830.2 ± 11.1 mgHA/cm³) compared to the C group (725.5 ± 12.1 mgHA/cm³, p < 0.05). Mechanical testing revealed superior compressive strength in the R group, with a rupture force of 312.5 ± 43.2 N versus 209.3 ± 35.4 N in the C group (p < 0.05). These results demonstrate romosozumab's capacity to promote robust bone formation and significantly enhance the mechanical integrity of the fusion mass.

CONCLUSION

Romosozumab treatment significantly improved bone healing, mineral density, and mechanical strength in a rat PLF model, suggesting its potential as a therapeutic option for enhancing spinal surgery outcomes. By promoting rapid bone formation and increasing bone strength, romosozumab addresses critical challenges such as pseudarthrosis and pedicle screw loosening, which frequently compromise surgical success, especially in osteoporotic patients. These findings underscore the therapeutic promise of romosozumab not only in spinal surgery but also as a broader intervention for bone repair and healing. Further research is needed to explore its dose-response relationship, long-term safety, and efficacy in osteoporotic models. Moreover, the use of biochemical markers and microstructural analyses will help elucidate the underlying mechanisms of its action. With its demonstrated ability to enhance both structural and functional bone properties, romosozumab offers a promising avenue for advancing spinal surgery and improving patient outcomes.

Mapping the sclerostin-LRP4 binding interface identifies critical interaction hotspots in loops 1 and 3 of sclerostin

The interaction of sclerostin (Scl) with the low-density lipoprotein receptor-related protein 4 (LRP4) leads to a marked reduction in bone formation by inhibiting the Wnt/β-catenin pathway. To characterize the Scl-LRP4 binding interface, we sorted a combinatorial library of Scl variants and isolated variants with reduced affinity to LRP4. We identified Scl single-mutation variants enriched during the sorting process and verified their reduction in affinity toward LRP4-a reduction that was not a result of changes in the variants' secondary structure or stability. We found that Scl positions K75 (loop 1) and V136 (loop 3) are critical hotspots for binding to LRP4. Our findings establish the foundation for targeting these hotspots for developing novel therapeutic strategies to promote bone formation.

Sclerostin and OPG/RANK-L system take part in bone remodeling in patients with acromegaly

Introduction

Acromegaly is a disease characterized by enhanced bone turnover with persistently high vertebral fracture risk. Sclerostin is a glycoprotein, which acts as an inhibitor of bone formation and activates osteoclast-mediated bone resorption. The osteoprotegerin (OPG)/receptor activator for the nuclear factor κ B ligand (RANK-L) system is crucial for controlling bone metabolism.

Objective

The study aimed primarily at evaluating sclerostin, OPG, and RANK-L concentrations in patients at different stages of acromegaly activity. The secondary aim was to identify an association of sclerostin with the OPG/RANK-L system and bone mineral density (BMD).

Materials and methods

The study enrolled 126 patients aged 40 to 80 years, including 72 patients with acromegaly and 54 controls (CG). The acromegaly patients were further classified into the following subgroups: active acromegaly (AA), controlled acromegaly (CTA), and cured acromegaly (CA). Blood samples were taken from the participants to measure sclerostin, OPG, RANK-L, growth hormone (GH), and insulin-like growth factor-1 (IGF-1). Dual-energy X-ray absorptiometry was performed at the lumbar spine and hip.

Results

Significantly lower sclerostin concentrations were observed in acromegaly patients compared with CG (AA, CTA, CA, CTA+CA, AA+CTA+CA vs CG; p < 0.001). Significant differences in OPG concentrations were revealed between the following groups: CTA vs CA (p=0.002), CTA vs CG (p<0.001), CTA+CA vs. CG (p<0.001), and AA+CTA+CA vs. CG (p<0.001). There were no significant differences in RANK-L concentrations between studied groups, regardless of the adopted classification (p>0.05). There were no statistically significant correlations between sclerostin and GH/IGF-1 or BMD. In the AA+CTA+CA group, there was a statistically significant positive correlation between SCL and OPG concentrations (r=0.271; p=0.022). A significant negative correlation between SCL and RANK-L was found in the AA group (r=-0.738; p=0.046).

Conclusions

Patients with acromegaly have lower sclerostin concentrations than healthy controls, which may be a result of a compensatory mechanism to increased bone loss. The influence of the GH/IGF-I axis on bone remodeling may be mediated in part by the OPG/RANK-L system. The interaction between SCL and OPG/RANK-L system in acromegaly should be further elucidated.

Nitric oxide contributes to rapid sclerostin protein loss following mechanical load

In response to mechanical loading of bone, osteocytes produce nitric oxide (NO•) and decrease sclerostin protein expression, leading to an increase in bone mass. However, it is unclear whether NO• production and sclerostin protein loss are mechanistically linked, and, if so, the nature of their hierarchical relationship within an established mechano-transduction pathway. Prior work showed that following fluid-shear stress (FSS), osteocytes produce NOX2-derived reactive oxygen species, inducing calcium (Ca2+) influx. Increased intracellular Ca2+ results in calcium-calmodulin dependent protein kinase II (CaMKII) activation, which regulates the lysosomal degradation of sclerostin protein. Here, we extend our discoveries, identifying NO• as a regulator of sclerostin degradation downstream of mechano-activated CaMKII. Pharmacological inhibition of nitric oxide synthase (NOS) activity in Ocy454 osteocyte-like cells prevented FSS-induced sclerostin protein loss. Conversely, short-term treatment with a NO• donor in Ocy454 cells or isolated murine long bones was sufficient to induce the rapid decrease in sclerostin protein abundance, independent of changes in Sost gene expression. Ocy454 cells express all three NOS genes, and transfection with siRNAs targeting eNOS/Nos3 was sufficient to prevent FSS-induced loss of sclerostin protein, while siRNAs targeting iNOS/Nos2 mildly blunted the loss of sclerostin but did not reach statistical significance. Similarly, siRNAs targeting both eNOS/Nos3 and iNOS/Nos2 prevented FSS-induced NO• production. Together, these data show iNOS/Nos2 and eNOS/Nos3 are the primary producers of FSS-dependent NO•, and that NO• is necessary and sufficient for sclerostin protein control. Further, selective inhibition of elements within this sclerostin-controlling mechano-transduction pathway indicated that NO• production occurs downstream of CaMKII activation. Targeting Camk2d and Camk2g with siRNA in Ocy454 cells prevented NO• production following FSS, indicating that CaMKII is needed for NO• production. However, NO• donation (1min) resulted in a significant increase in CaMKII activation, suggesting that NO• may have the ability to tune CaMKII response. Together, these data support that CaMKII is necessary for, and may be modulated by NO•, and that the interaction of these two signals is involved in the control of sclerostin protein abundance, consistent with a role in bone anabolic responses.

Unraveling the molecular and immunological landscape: Exploring signaling pathways in osteoporosis

Osteoporosis, characterized by compromised bone density and microarchitecture, represents a significant global health challenge, particularly in aging populations. This comprehensive review delves into the intricate signaling pathways implicated in the pathogenesis of osteoporosis, providing valuable insights into the pivotal role of signal transduction in maintaining bone homeostasis. The exploration encompasses cellular signaling pathways such as Wnt, Notch, JAK/STAT, NF-κB, and TGF-β, all of which play crucial roles in bone remodeling. The dysregulation of these pathways is a contributing factor to osteoporosis, necessitating a profound understanding of their complexities to unveil the molecular mechanisms underlying bone loss. The review highlights the pathological significance of disrupted signaling in osteoporosis, emphasizing how these deviations impact the functionality of osteoblasts and osteoclasts, ultimately resulting in heightened bone resorption and compromised bone formation. A nuanced analysis of the intricate crosstalk between these pathways is provided to underscore their relevance in the pathophysiology of osteoporosis. Furthermore, the study addresses some of the most crucial long non-coding RNAs (lncRNAs) associated with osteoporosis, adding an additional layer of academic depth to the exploration of immune system involvement in various types of osteoporosis. Finally, we propose that SKP1 can serve as a potential biomarker in osteoporosis.

Romosozumab versus parathyroid hormone receptor agonists: which osteoanabolic to choose and when?

Osteoanabolic agents are used as a first line treatment in patients at high fracture risk. The PTH receptor 1 (PTH1R) agonists teriparatide (TPTD) and abaloparatide (ABL) increase bone formation, bone mineral density (BMD), and bone strength by activating PTH receptors on osteoblasts. Romosozumab (ROMO), a humanized monoclonal antibody against sclerostin, dramatically but transiently stimulates bone formation and persistently reduces bone resorption. Osteoanabolic agents increase BMD and bone strength while being more effective than antiresorptives in reducing fracture risk in postmenopausal women. However, direct comparisons of the antifracture benefits of osteoanabolic therapies are limited. In a direct comparison of TPTD and ABL, the latter resulted in greater BMD increases at the hip. While no differences in vertebral or non-vertebral fracture risk were observed between the two drugs, ABL led to a greater reduction of major osteoporotic fractures. Adverse event profiles were similar between the two agents except for hypercalcemia, which occurred more often with TPTD. No direct comparisons of fracture risk reduction between ROMO and the PTH1R agonists exist. Individual studies have shown greater increases in BMD and bone strength with ROMO compared with TPTD in treatment-naive women and in women previously treated with bisphosphonates. Some safety aspects, such as a history of tumor precluding the use of PTH1R agonists, and a history of major cardiovascular events precluding the use of ROMO, should also be considered when choosing between these agents. Finally, convenience of administration, reimbursement by national health systems and length of clinical experience may influence patient choice.

Wnt pathway in bone: knowledge structure and hot spots from 1993 to 2022

Background: The role of the Wnt pathway in bone and its targets in skeletal disease has garnered interest, but the field lacks a systematic analysis of research. This paper presents a bibliometric study of publications related to the Wnt signaling pathway in bone to describe the current state of study and predict future outlooks. Methods: All relevant articles and reviews from 1993 to 2022 were collected from the Web of Science Core Collection (WoSCC). Bibliometric analysis and visualization were performed using CiteSpace 6.1 R3, VOSviewer 1.6.15, and the Online Analysis Platform of Literature Metrology (http://bibliometric.com/). Results: A total of 7,184 papers were retrieved, authored by 28,443 researchers from 89 countries/regions and published in 261 academic journals. The annual publication numbers peaked in 2021. China and United States are the leading countries, with the University of California and Harvard University as the most active institutions. Wang, Yang is the most prolific author. Bone has the most published research, while Proceedings of the National Academy of Sciences of the United States is the most cited journal on average. The main keywords include expression, Wnt, osteoporosis, bone, and osteogenic differentiation. Current and developing research hotspots focus on bone mass, sclerostin antibody, multiple myeloma, and cartilage development. Conclusion: This paper provides new insights for researchers to delve into the mechanisms of Wnt and bone related diseases and translate into clinical studies. It reveals the development and future research trends in Wnt and skeletal-related studies.

Buds of new bone formation within the Femoral Head of Hip Fracture Patients Coincide with Zones of Low Osteocyte Sclerostin

Romosozumab treatment reduces the rate of hip fractures and increases hip bone density, increasing bone formation by inhibiting sclerostin protein. We studied the normal pattern of bone formation and osteocyte expression in the human proximal femur because it is relevant to both antisclerostin treatment effects and fracture. Having visualized and quantified buds of new bone formation in trabeculae, we hypothesized that they would coincide with areas of (a) higher mechanical stress and (b) low sclerostin expression by osteocytes. In patients with hip fracture, we visualized each bud of active modeling-based formation (forming minimodeling structure [FMiS]) in trabecular cores taken from different parts of the femoral head. Trabecular bone structure was also measured with high-resolution imaging. More buds of new bone formation (by volume) were present in the higher stress superomedial zone (FMiS density, N.FMiS/T.Ar) than lower stress superolateral (p < 0.05), and inferomedial (p < 0.001) regions. There were fewer sclerostin expressing osteocytes close to or within FMiS. FMiS density correlated with greater amount, thickness, number, and connectivity of trabeculae (bone volume BV/TV, r = 0.65, p < 0.0001; bone surface BS/TV, r = 0.47, p < 0.01; trabecular thickness Tb.Th, r = 0.55, p < 0.001; trabecular number Tb.N, r = 0.47, p < 0.01; and connectivity density Conn.D, r = 0.40, p < 0.05) and lower trabecular separation (Tb.Sp, r = -0.56, p < 0.001). These results demonstrate modeling-based bone formation in femoral trabeculae from patients with hip fracture as a potential therapeutic target to enhance bone structure. © 2023 American Society for Bone and Mineral Research (ASBMR).

Male Runners With Lower Energy Availability Have Impaired Skeletal Integrity Compared to Nonathletes

CONTEXT

Female athletes, particularly runners, with insufficient caloric intake for their energy expenditure [low energy availability (EA) or relative energy deficiency] are at risk for impaired skeletal integrity. Data are lacking in male runners.

OBJECTIVE

To determine whether male runners at risk for energy deficit have impaired bone mineral density (BMD), microarchitecture, and estimated strength.

DESIGN

Cross-sectional.

SETTING

Clinical research center.

PARTICIPANTS

39 men (20 runners, 19 controls), ages 16-30 years.

MAIN OUTCOME MEASURES

Areal BMD (dual-energy x-ray absorptiometry); tibia and radius volumetric BMD and microarchitecture (high-resolution peripheral quantitative computed tomography); failure load (microfinite element analysis); serum testosterone, estradiol, leptin; energy availability.

RESULTS

Mean age (24.5 ± 3.8 y), lean mass, testosterone, and estradiol levels were similar; body mass index, percent fat mass, leptin, and lumbar spine BMD Z-score (-1.4 ± 0.8 vs -0.8 ± 0.8) lower (P < .05); and calcium intake and running mileage higher (P ≤ .01) in runners vs controls. Runners with EA

CONCLUSIONS

Despite weight-bearing activity, skeletal integrity is impaired in male runners with lower caloric intake relative to exercise energy expenditure, which may increase bone stress injury risk. Lower estradiol and lean mass are associated with lower tibial strength in runners.

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Key Words

• HR-pQCT
• athletes
• bone density
• energy availability

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MESH Headings

• Humans
• Male
• Female
• Leptin
• Cross-Sectional Studies
• Calcium
• Bone Density
• Absorptiometry, Photon
• Lumbar Vertebrae
• Testosterone
• Estradiol

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Grants

• K23 DK115903 NIDDK NIH HHS
• K24 HD071843 NICHD NIH HHS
• 1UL1TR002541-01 NIH HHS
• K24 HL092902 NHLBI NIH HHS
• Massachusetts General Hospital Executive Committee on Research
• National Institutes of Health
• Department of Defense Research Participation Program
• U.S. Army Research Institute of Environmental Medicine
• Oak Ridge Institute for Science and Education

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Affiliation(s)

Melanie S Haines Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Harvard Medical School, Boston, MA 02115, USA
Snimarjot Kaur Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Harvard Medical School, Boston, MA 02115, USA
Geetanjali Scarff Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA
Meghan Lauze Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA
Anu Gerweck Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA
Meghan Slattery Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA
Nicolas M Oreskovic Harvard Medical School, Boston, MA 02115, USA Department of Internal Medicine and Pediatrics, Massachusetts General Hospital, Boston, MA 02114, USA
Kathryn E Ackerman Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Harvard Medical School, Boston, MA 02115, USA Female Athlete Program, Division of Sports Medicine, Boston Children's Hospital, Boston, MA 02115, USA
Adam S Tenforde Harvard Medical School, Boston, MA 02115, USA Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital, Cambridge, MA 02129, USA
Kristin L Popp Harvard Medical School, Boston, MA 02115, USA Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Military Performance Division, United States Army Research Institute of Environmental Medicine, Natick, MA 01760, USA Department of Energy, Oak Ridge Institute for Science and Education, Oak Ridge, TN 37830, USA
Mary L Bouxsein Harvard Medical School, Boston, MA 02115, USA Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Center for Advanced Orthopedic Studies, Beth Israel Deaconess Medical Center, Boston, MA 02115, USA
Karen K Miller Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Harvard Medical School, Boston, MA 02115, USA
Madhusmita Misra Neuroendocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Harvard Medical School, Boston, MA 02115, USA Division of Pediatric Endocrinology, Massachusetts General Hospital, Boston, MA 02114, USA

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Collaborators Collapse

Meta-analysis of the effects of denosumab and romosozumab on bone mineral density and turnover markers in patients with osteoporosis

Purpose

To assess the alterations in bone mineral density and bone turnover marker concentrations following the administration of denosumab and romosozumab therapies in patients with osteoporosis.

Methods

PubMed was searched for studies published until January 28, 2023, that investigated the clinical efficacy and bone turnover marker changes of denosumab and romosozumab in the treatment of osteoporosis, with a minimum follow-up of 3 months in each study. Studies were screened, and data on changes in bone mineral density (BMD), P1NP, and TRACP-5b levels after treatment were extracted and included in the analysis.

Results

Six studies were analyzed. At 3 months after treatment, the romosozumab group showed greater changes in lumbar BMD and bone turnover markers. BMD of total hip and femoral neck was relatively delayed. Beginning at 6 to 12 months, romosozumab showed greater changes in bone mineral density and markers of bone turnover.

Conclusion

Both romosozumab and denosumab have antiosteoporotic effects, with greater effects on BMD and bone turnover markers observed within 12 months of romosozumab treatment.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero, identifier CRD42023395034.

Assessment of sclerostin levels in the gingival crevicular fluid of patients with periodontitis: A clinico-biochemical crosssectional study

Background

Sclerostin, a glycoprotein, plays a key role in regulating bone mass. In this study, sclerostin levels in the gingival crevicular fluid (GCF) were assessed in patients with Stage III Grade C generalized periodontitis (SIII-GC) and Stage III Grade B generalized periodontitis (SIII-GB).

Methods

This cross-sectional study included 30 participants divided equally into three groups: group I (gingival health), group II (SIII-GC), and group III (SIII-GB). Clinical periodontal parameters like plaque index (PI), gingival bleeding index (GBI), probing pocket depth (PD), and clinical attachment level (CAL) were recorded. A sandwich ELISA was used to determine the sclerostin levels in GCF samples. One-way ANOVA and post hoc Tukey tests were used to analyze the clinical parameters and GCF sclerostin levels. The association between GCF sclerostin levels and periodontal parameters was assessed using Pearson's correlation coefficient (r).

Results

Patients in groups II and III had much higher sclerostin levels in their GCF than in group I (P≤0.05). In contrast, no significant difference in sclerostin levels was observed between the two diseased conditions (P=0.841). Concerning periodontal parameters, a statistically significant difference was observed between the three groups. There was a positive correlation between the periodontal clinical parameters and the expression levels of sclerostin in GCF (P≤0.05).

Conclusion

Increased expression of sclerostin in GCF in patients with periodontitis indicated that it could be considered a reliable biomarker of periodontal disease activity.

Targeting strategies for bone diseases: signaling pathways and clinical studies

Since the proposal of Paul Ehrlich's magic bullet concept over 100 years ago, tremendous advances have occurred in targeted therapy. From the initial selective antibody, antitoxin to targeted drug delivery that emerged in the past decades, more precise therapeutic efficacy is realized in specific pathological sites of clinical diseases. As a highly pyknotic mineralized tissue with lessened blood flow, bone is characterized by a complex remodeling and homeostatic regulation mechanism, which makes drug therapy for skeletal diseases more challenging than other tissues. Bone-targeted therapy has been considered a promising therapeutic approach for handling such drawbacks. With the deepening understanding of bone biology, improvements in some established bone-targeted drugs and novel therapeutic targets for drugs and deliveries have emerged on the horizon. In this review, we provide a panoramic summary of recent advances in therapeutic strategies based on bone targeting. We highlight targeting strategies based on bone structure and remodeling biology. For bone-targeted therapeutic agents, in addition to improvements of the classic denosumab, romosozumab, and PTH1R ligands, potential regulation of the remodeling process targeting other key membrane expressions, cellular crosstalk, and gene expression, of all bone cells has been exploited. For bone-targeted drug delivery, different delivery strategies targeting bone matrix, bone marrow, and specific bone cells are summarized with a comparison between different targeting ligands. Ultimately, this review will summarize recent advances in the clinical translation of bone-targeted therapies and provide a perspective on the challenges for the application of bone-targeted therapy in the clinic and future trends in this area.

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.

Targeting loop3 of sclerostin preserves its cardiovascular protective action and promotes bone formation

Sclerostin negatively regulates bone formation by antagonizing Wnt signalling. An antibody targeting sclerostin for the treatment of postmenopausal osteoporosis was approved by the U.S. Food and Drug Administration, with a boxed warning for cardiovascular risk. Here we demonstrate that sclerostin participates in protecting cardiovascular system and inhibiting bone formation via different loops. Loop3 deficiency by genetic truncation could maintain sclerostin’s protective effect on the cardiovascular system while attenuating its inhibitory effect on bone formation. We identify an aptamer, named aptscl56, which specifically targets sclerostin loop3 and use a modified aptscl56 version, called Apc001PE, as specific in vivo pharmacologic tool to validate the above effect of loop3. Apc001PE has no effect on aortic aneurysm and atherosclerotic development in ApoE−/− mice and hSOSTki.ApoE−/− mice with angiotensin II infusion. Apc001PE can promote bone formation in hSOSTki mice and ovariectomy-induced osteoporotic rats. In summary, sclerostin loop3 cannot participate in protecting the cardiovascular system, but participates in inhibiting bone formation.

Osteoporosis and Fragility Fractures: currently available pharmacological options and future directions

Osteoporosis is a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture. The average lifetime risk of a 50-year-old woman to suffer a fracture of the spine, hip, proximal humerus, or distal forearm has been estimated at close to 50%. In general, pharmacological treatment is recommended in patients who suffered a fragility fracture because their risk of suffering a subsequent fracture is increased dramatically. Therefore, many guidelines recommend pharmacological treatment in patients without a prevalent fracture if their fracture probability is comparable to or higher than that of a person of the same age with a prevalent fracture. The present review aims to highlight currently available pharmacological treatment options and their antifracture efficacy including safety aspects. Drug classes discussed comprise bisphosphonates, selective estrogen receptor modulators, parathyroid hormone peptides and derivatives, humanized monoclonal antibodies, and estrogens and gestagens and their combinations. Furthermore, a brief glimpse is provided into a potentially promising treatment option that involves mesenchymal stem cells.

Baduanjin exercise: A potential promising therapy toward osteoporosis

Purpose

Baduanjin (BDJ) exercise is a traditional exercise that combines breathing, body movement, meditation and awareness to help delay the onset and progression of senile degenerative musculoskeletal diseases, such as osteoporosis (OP). The aim of this meta-analysis is to evaluate the efficacy of BDJ exercise, and preliminarily infer its effective mechanism in the treatment of OP.

Methods

We identified relevant randomized controlled trials (RCTs) through eight databases, and compared BDJ exercise with the control groups (including blank control and conventional treatment intervention). The main outcome measure was bone mineral density (BMD), the additional outcome measures were visual analogue scale (VAS), Berg balance scale (BBS), serum Calcium (Ca), serum Phosphorus (P), serum Alkaline phosphatase (ALP), and serum bone gla protein (BGP). Meta-analysis and trial sequence analysis (TSA) were performed using RevMan 5.4, Stata 16.0, and TSA 0.9.

Results

In total, 13 RCTs involving 919 patients were included in the analysis. For postmenopausal osteoporosis, BDJ exercise alone and BDJ exercise combined with conventional treatment can improve the BMD of lumbar spine. BDJ exercise alone can influence serum Ca and ALP. BDJ exercise combined with conventional treatment can improve balance (BBS) and influence serum BGP. For senile osteoporosis, BDJ exercise alone and BDJ exercise combined with conventional treatment can improve balance (BBS). BDJ exercise combined with conventional treatment can improve the BMD of hip and pain relieve (VAS). For primary osteoporosis, BDJ exercise combined with conventional treatment can improve the BMD of lumbar spine and femoral neck.

Conclusion

Baduanjin exercise may be beneficial to improve BMD, relieve pain, improve balance ability, influence serum BGP and serum ALP in patients with OP, but differences occur due to various types of OP. Due to the low quality of research on the efficacy and mechanism of BDJ exercise in the treatment of OP, high-quality evidence-based research is still needed to provide reliable supporting evidence.

Systematic Review Registration

[http://www.crd.york.ac.uk/PROSPERO], identifier [CRD42022329022].

Potential donor-dependent regulative effects of endogenous sclerostin expression and mineralization potential in primary human PDL cells in vitro

OBJECTIVES

The glycoprotein sclerostin is mostly expressed in osteocytes and plays a central role in human bone metabolism. However, sclerostin and the corresponding SOST gene have been found in periodontal ligament cells under mineralizing conditions as well. The present study aimed to investigate, whether there was a correlation between endogenous SOST expression, the corresponding gene, and mineralization potential in human periodontal ligament cells and to identify different sclerostin expression and secretion patterns in cells derived from individual donors.

MATERIAL AND METHODS

Primary human periodontal ligament cells of three different donors were cultivated under control or mineralizing conditions for 6, 13, 15 and 18 days, respectively. Calcium deposits were stained with alizarin red and quantified afterwards. Quantitative expression analysis of the SOST gene encoding sclerostin was performed using quantitative reverse transcription polymerase chain reaction (RT-PCR). Additionally, intracellular sclerostin expression was analyzed using Western blotting and extracellular sclerostin secretion was quantified using Enzyme-linked Immunosorbent Assay (ELISA).

RESULTS

Alizarin red staining identified calcium deposits in periodontal ligament cells under mineralizing conditions beginning from day 13, relative SOST expression occurred on day 6. Whereas staining continued to increase in donor 1 on day 15, it remained stable in donors 2 and 3. Conversely, baseline SOST expression was significantly lower in donor 1 compared to donors 2 and 3. Western blotting and ELISA revealed increased intra- and extracellular sclerostin expression at day 13 under mineralizing conditions. Donor 3 exhibited the highest overall sclerostin levels.

CONCLUSIONS

Our data emphasize donor-specific characteristics in differentiation potential and sclerostin expression patterns in primary human periodontal ligament cells. Sclerostin might play a central role in modulating osteogenic differentiation in periodontal ligament cells as part of a negative feedback mechanism in avoiding excessive mineralization.

Advances in Our Understanding of the Mechanism of Action of Drugs (including Traditional Chinese Medicines) for the Intervention and Treatment of Osteoporosis

Osteoporosis (OP) is known as a silent disease in which the loss of bone mass and bone density does not cause obvious symptoms, resulting in insufficient treatment and preventive measures. The losses of bone mass and bone density become more severe over time and an only small percentage of patients are diagnosed when OP-related fractures occur. The high disability and mortality rates of OP-related fractures cause great psychological and physical damage and impose a heavy economic burden on individuals and society. Therefore, early intervention and treatment must be emphasized to achieve the overall goal of reducing the fracture risk. Anti-OP drugs are currently divided into three classes: antiresorptive agents, anabolic agents, and drugs with other mechanisms. In this review, research progress related to common anti-OP drugs in these three classes as well as targeted therapies is summarized to help researchers and clinicians understand their mechanisms of action and to promote pharmacological research and novel drug development.

Sclerostin is a promising therapeutic target for oral inflammation and regenerative dentistry

Sclerostin is the protein product of the SOST gene and is known for its inhibitory effects on bone formation. The monoclonal antibody against sclerostin has been approved as a novel treatment method for osteoporosis. Oral health is one of the essential aspects of general human health. Hereditary bone dysplasia syndrome caused by sclerostin deficiency is often accompanied by some dental malformations, inspiring the therapeutic exploration of sclerostin in the oral and dental fields. Recent studies have found that sclerostin is expressed in several functional cell types in oral tissues, and the expression level of sclerostin is altered in pathological conditions. Sclerostin not only exerts similar negative outcomes on the formation of alveolar bone and bone-like tissues, including dentin and cementum, but also participates in the development of oral inflammatory diseases such as periodontitis, pulpitis, and peri-implantitis. This review aims to highlight related research progress of sclerostin in oral cavity, propose necessary further research in this field, and discuss its potential as a therapeutic target for dental indications and regenerative dentistry.

Wnt Pathway Extracellular Components and Their Essential Roles in Bone Homeostasis

The Wnt pathway is involved in several processes essential for bone development and homeostasis. For proper functioning, the Wnt pathway is tightly regulated by numerous extracellular elements that act by both activating and inhibiting the pathway at different moments. This review aims to describe, summarize and update the findings regarding the extracellular modulators of the Wnt pathway, including co-receptors, ligands and inhibitors, in relation to bone homeostasis, with an emphasis on the animal models generated, the diseases associated with each gene and the bone processes in which each member is involved. The precise knowledge of all these elements will help us to identify possible targets that can be used as a therapeutic target for the treatment of bone diseases such as osteoporosis.

The Effects of Osteoporotic and Non-osteoporotic Medications on Fracture Risk and Bone Mineral Density

Osteoporosis is a highly prevalent bone disease affecting more than 37.5 million individuals in the European Union (EU) and the  United States of America (USA). It is characterized by low bone mineral density (BMD), impaired bone quality, and loss of structural and biomechanical properties, resulting in reduced bone strength. An increase in morbidity and mortality is seen in patients with osteoporosis, caused by the approximately 3.5 million new osteoporotic fractures occurring every year in the EU. Currently, different medications are available for the treatment of osteoporosis, including anti-resorptive and osteoanabolic medications. Bisphosphonates, which belong to the anti-resorptive medications, are the standard treatment for osteoporosis based on their positive effects on bone, long-term experience, and low costs. However, not only medications used for the treatment of osteoporosis can affect bone: several other medications are suggested to have an effect on bone as well, especially on fracture risk and BMD. Knowledge about the positive and negative effects of different medications on both fracture risk and BMD is important, as it can contribute to an improvement in osteoporosis prevention and treatment in general, and, even more importantly, to the individual's health. In this review, we therefore discuss the effects of both osteoporotic and non-osteoporotic medications on fracture risk and BMD. In addition, we discuss the underlying mechanisms of action.

Sclerostin and bone remodeling biomarkers responses to whole-body cryotherapy (- 110 °C) in healthy young men with different physical fitness levels

We investigated the effects of single and repeated exposures to whole-body cryotherapy on biomarkers of bone remodeling and osteo-immune crosstalk: sclerostin, osteocalcin (OC), C-terminal cross-linked telopeptide of type I collagen (CTx-I), osteoprotegerin (OPG) and free soluble receptor activator for nuclear factor κ B ligand (sRANKL). The study included 22 healthy males, grouped in high physical fitness level (HPhL) and low physical fitness level (LPhL), all undergone 10 consecutive sessions in a cryogenic chamber (- 110 °C). We observed a significant time-effect on sclerostin (p < 0.05), OC (p < 0.01), CTx-I (p < 0.001), OC/CTx-I (p < 0.05), and significant differences in sRANKL between the groups (p < 0.05) after the 1st cryostimulation; a significant time-effect on OC (p < 0.001) and OC/CTx-I (p < 0.001) after the 10th cryostimulation, and a significant time-effect on CTx-I (p < 0.001) and OC/CTx-I (p < 0.01) after 10 sessions of WBC. In conclusion, in young men, the first exposure to extreme cold induced significant changes in serum sclerostin. The changes in sRANKL, between groups, suggest that fitness level may modify the body's response to cold. The effects of the first stimulus and the whole session are not identical, probably due to the physiological development of habituation to cold.

BMP antagonists in tissue development and disease

Bone morphogenic proteins (BMPs) are important growth regulators in embryogenesis and postnatal homeostasis. Their tight regulation is crucial for successful embryonic development as well as tissue homeostasis in the adult organism. BMP inhibition by natural extracellular biologic antagonists represents the most intensively studied mechanistic concept of BMP growth factor regulation. It was shown to be critical for numerous developmental programs, including germ layer specification and spatiotemporal gradients required for the establishment of the dorsal-ventral axis and organ formation. The importance of BMP antagonists for extracellular matrix homeostasis is illustrated by the numerous human connective tissue disorders caused by their mutational inactivation. Here, we will focus on the known functional interactions targeting BMP antagonists to the ECM and discuss how these interactions influence BMP antagonist activity. Moreover, we will provide an overview about the current concepts and investigated molecular mechanisms modulating BMP inhibitor function in the context of development and disease.

Diabetes and Osteoporosis: Part I, Epidemiology and Pathophysiology

Both diabetes and osteoporosis are increasingly prevalent diseases, in part owing to aging populations worldwide. Epidemiologic data have shown that other organs may be adversely affected by diabetes, including the skeleton, in what has become known as diabetes-induced osteoporosis, which represents the combined impact of conventional osteoporosis with the additional fracture burden attributed to diabetes. There is an increased risk of fracture in patients with Type 1 and Type 2 diabetes, and some antidiabetic medications also may contribute to increased risk of fracture in diabetes.

Sclerostin and its role as a bone modifying agent in periodontal disease

BACKGROUND

Periodontitis is a highly prevalent inflammatory disease affecting the periodontium that results from an imbalance between periodontopathogens and host mechanisms. Continuous progression of the disease may lead to tissue and bone destruction, eventually resulting in tooth loss. The extent of bone loss depends on the dysregulated host immune response. Various host-elicited molecules play a major role in disease progression. The discovery of the glycoprotein sclerostin and its role as a regulator of bone mass has led to a better understanding of bone metabolism.

HIGHLIGHT

Sclerostin, which is primarily expressed by osteocytes, is a negative regulator of bone formation. It is a potent antagonist of the canonical Wingless-related integration site (Wnt) pathway, which is actively involved in bone homeostasis. Sclerostin is known to stimulate bone resorption by altering the osteoprotegerin (OPG)/receptor activator of nuclear factor kappa- β ligand (RANKL) balance. Additionally, in periodontitis, activation of the inflammatory cascade also increases the synthesis of sclerostin.

CONCLUSION

The recently discovered sclerostin antibody has emerged as a positive therapeutic tool for the treatment of metabolic bone diseases. It has been reported to improve bone strength, bone formation, osseointegration around implants and lower the risk of bone fractures in various animal and human models. This review describes the properties and action of sclerostin, its role in periodontal diseases, and the advent and efficacy of sclerostin antibodies.

The Roles of Sclerostin in Immune System and the Applications of Aptamers in Immune-Related Research

Wnt signaling is one of the fundamental pathways that play a major role in almost every aspect of biological systems. In addition to the well-known influence of Wnt signaling on bone formation, its essential role in the immune system also attracted increasing attention. Sclerostin, a confirmed Wnt antagonist, is also proven to modulate the development and differentiation of normal immune cells, particularly B cells. Aptamers, single-stranded (ss) oligonucleotides, are capable of specifically binding to a variety of target molecules by virtue of their unique three-dimensional structures. With in-depth study of those functional nucleic acids, they have been gradually applied to diagnostic and therapeutic area in immune diseases due to their various advantages over antibodies. In this review, we focus on several issues including the roles of Wnt signaling and Wnt antagonist sclerostin in the immune system. For the sake of understanding, current examples of aptamers applications for the immune diseases are also discussed. At the end of this review, we propose our ideas for the future research directions.

Characterization of the different oligomeric states of the DAN family antagonists SOSTDC1 and SOST

The DAN (differential screening-selected gene aberrative in neuroblastoma) family are a group of secreted extracellular proteins which typically bind to and antagonize BMP (bone morphogenetic protein) ligands. Previous studies have revealed discrepancies between the oligomerization state of certain DAN family members, with SOST (a poor antagonist of BMP signaling) forming a monomer while Grem1, Grem2, and NBL1 (more potent BMP antagonists) form non-disulfide linked dimers. The protein SOSTDC1 (Sclerostin domain containing protein 1) is sequentially similar to SOST, but has been shown to be a better BMP inhibitor. In order to determine the oligomerization state of SOSTDC1 and determine what effect dimerization might have on the mechanism of DAN family antagonism of BMP signaling, we isolated the SOSTDC1 protein and, using a battery of biophysical, biochemical, and structural techniques, showed that SOSTDC1 forms a highly stable non-covalent dimer. Additionally, this SOSTDC1 dimer was shown, using an in vitro cell based assay system, to be an inhibitor of multiple BMP signaling growth factors, including GDF5, while monomeric SOST was a very poor antagonist. These results demonstrate that SOSTDC1 is distinct from paralogue SOST in terms of both oligomerization and strength of BMP inhibition.

MicroRNA-21 facilitates osteoblast activity

MicroRNAs are emerging as critical post-transcriptional modulators in bone remodeling, regulating the functions of osteoblasts and osteoclasts. Intercellular crosstalk between osteoblasts and osteoclasts is mediated by miR-21 that controls the bone homeostasis response, providing potential targets for the maintenance of osteoblast function. The aim of this study was to investigate the effects of miR-21 on osteoblast function, and to explore the underlying mechanism. Increased alkaline phosphatase (ALP) activity and accelerated matrix mineralization was observed in mouse pre-osteoblast MC3T3-E1 cells compared with the non-induction (control) group. MiR-21 positively regulates osteogenic differentiation and mineralization by facilitating the expression of key osteogenic factors (ALP, Runx2, Osteopontin (OPN), Osterix (OSX) and Mef2c) in MC3T3-E1 cells. Furthermore, a deficiency of miR-21 suppresses the expression of those factors at both the mRNA and protein levels, indicating that miR-21 is a positive regulator of osteoblastic differentiation. H-E staining, Azan staining, Masson's Trichrome staining and Toluidine blue staining were performed in jaw and femur tissues of miR-21 knockout (miR-21KO) and wild-type (WT) mice. Immunohistochemical staining revealed substantially lower levels of ALP, Runx2 and OSX expression in jaw and femur tissues of miR-21KO mice. A similar trend was observed in femur tissues using quantitative real-time (RT) PCR. A total of 17 osteogenesis-related mRNAs were found to be differentially expressed in miR-21KO femur tissues using Mouse Gene Expression Microarray analysis. GeneSpring and Ingenuity Pathway Analysis revealed several potential target genes that are involved in bone remodeling, such as IL-1β and HIF-1α. Several important pathways were determined to be facilitators of miR-21, which provides a reliable reference for future studies to elucidate the biological mechanisms of osteoblast function. Taken together, these results lead us to hypothesize a potential role for miR-21 in regulating osteoblast function, thus representing a potential biomarker of osteogenesis.

The Effects of Sclerostin on the Immune System

PURPOSE OF REVIEW

We reviewed recent progress on the role of sclerostin (SOST) and its effects on the immune system in order to summarize the current state of knowledge in osteoimmunology, in regard to hematopoiesis, lymphopoiesis, and inflammation.

RECENT FINDINGS

Changes in sclerostin levels affect distinct niches within the bone marrow that support hematopoietic stem cells and B cell development. Sclerostin's regulation of adipogenesis could also be important for immune cell maintenance with age. Surprisingly, B cell development in the bone marrow is influenced by Sost produced by mesenchymal stem cells and osteoblasts, but not by osteocytes. Additionally, extramedullary hematopoiesis in the spleen and increased pro-inflammatory cytokine levels in the bone marrow are observed in global Sost^-/- mice. In addition to changes in bone marrow density, sclerostin depletion affects B lymphopoiesis and myelopoiesis, as well as other changes within the bone marrow cavity that could affect hematopoiesis. It is therefore important to monitor for hematopoietic changes in patients receiving sclerostin-depleting therapies.

Anatomical similarity between the Sost-knockout mouse and sclerosteosis in humans

Sclerosteosis, a rare autosomal recessive genetic disorder caused by a mutation of the Sost gene, manifests in the facial skeleton by gigantism, facial distortion, mandibular prognathism, cranial nerve palsy, and, in extreme cases, compression of the medulla oblongata. Mice lacking sclerostin reflect some symptoms of sclerosteosis, but this is the first report of the effect on the facial skeleton. We used geometric morphometrics (GMM) to analyze the deformations of the murine facial skeleton from the wild‐type to the Sost gene knockout. Landmark coordinates were obtained by surface reconstructions from micro‐computed tomography. Centroid size, principal component scores in shape space and form space, and asymmetry were computed by the standard GMM formulas, and dental and skeletal jaw lengths were examined as ratios. We show here that, compared to wild type controls, mice lacking Sost have larger centroid size (effect size, p‐value: 4.59, <.001), higher mean asymmetry (1.14, .065), dental and skeletal mandibular prognathism (1.36, .010 and 5.92, <.001), a smaller foramen magnum (−1.71, .015), and calvaria that are more highly curved (form space p = 4.09, .002; shape space p = 12.82, .002). These features of mice lacking sclerostin largely correspond to the changes of the facial skeleton observed in sclerosteosis. This alignment further supports claims that the Sost gene plays a fundamental role in bony facial development in rodents and humans alike.

Interactions between Sclerostin and Glycosaminoglycans

Sclerostin (SOST) is a glycoprotein having many important functions in the regulation of bone formation as a key negative regulator of Wnt signaling in bone. Surface plasmon resonance (SPR), which allows for a direct quantitative analysis of the label-free molecular interactions in real-time, has been widely used for the biophysical characterization of glycosaminoglycan (GAG)-protein interactions. In the present study, we report kinetics, structural analysis and the effects of physiological conditions (e.g., salt concentrations, Ca²⁺ and Zn²⁺concentrations) on the interactions between GAGs and recombinant human (rh) and recombinant mouse (rm) SOST using SPR. SPR results revealed that both SOSTs bind heparin with high affinity (rhSOST-heparin, K_D~36 nM and rmSOST-heparin, K_D~77 nM) and the shortest oligosaccharide of heparin that effectively competes with full size heparin for SOST binding is octadecasaccharide (18mer). This heparin binding protein also interacts with other highly sulfated GAGs including, disulfated-dermatan sulfate and chondroitin sulfate E. In addition, liquid chromatography-mass spectrometry was used to characterize the structure of sulfated GAGs that bound to SOST.

Monoclonal antibodies against RANKL and sclerostin for myeloma-related bone disease: can they change the standard of care?

Introduction: Over 80% of the patients with multiple myeloma (MM) develop myeloma bone disease (MBD) during the disease course. The clinical consequences include serious skeletal-related events (SRE) that impact survival and quality of life. Bisphosphonates are the mainstay in the treatment of MBD. Currently, new therapeutic strategies are being introduced and broaden the therapeutic options in MBD. Areas covered: The purpose of this review is to summarize the current clinical management of MBD and present novel data regarding monoclonal antibodies against the receptor activator of NF-kappa B ligand (RANKL) and sclerostin that may change the clinical practice. Expert opinion: Our better understanding of the pathophysiology of MBD has identified several factors as potential therapeutic targets. Recent data have shown that the RANKL inhibitor denosumab constitutes a new promising option. The non-inferiority compared with bisphosphonates in terms of SRE prevention, the potential survival benefit, the convenience of subcutaneous administration, and the favorable toxicity profile makes denosumab a valuable alternative for physicians in the current treatment of MBD. Anti-sclerostin antibodies are currently under clinical development. Further investigations are needed to address open questions in the field including the value of anabolic agents combined with anti-resorptive and anti-MM drugs in MBD.

Role of intracellular Ca2+-based mechanotransduction of human periodontal ligament fibroblasts

Human periodontal ligament (hPDL) fibroblasts are thought to receive mechanical stress (MS) produced by orthodontic tooth movement, thereby regulating alveolar bone remodeling. However, the role of intracellular calcium ([Ca²⁺]_i)-based mechanotransduction is not fully understood. We explored the MS-induced [Ca²⁺]_i responses both in isolated hPDL fibroblasts and in intact hPDL tissue and investigated its possible role in alveolar bone remodeling. hPDL fibroblasts were obtained from healthy donors' premolars that had been extracted for orthodontic reasons. The oscillatory [Ca²⁺]_i activity induced by static compressive force was measured by a live-cell Ca²⁺ imaging system and evaluated by several feature extraction method. The spatial pattern of cell-cell communication was investigated by Moran's I, an index of spatial autocorrelation and the gap junction (GJ) inhibitor. The Ca²⁺-transporting ionophore A23187 was used to further investigate the role of [Ca²⁺]_i up-regulation in hPDL cell behavior. hPDL fibroblasts displayed autonomous [Ca²⁺]_i responses. Compressive MS activated this autonomous responsive behavior with an increased percentage of responsive cells both in vitro and ex vivo. The integration, variance, maximum amplitude, waveform length, and index J in the [Ca²⁺]_i responses were also significantly increased, whereas the mean power frequency was attenuated in response to MS. The increased Moran's I after MS indicated that MS might affect the pattern of cell-cell communication via GJs. Similar to the findings of MS-mediated regulation, the A23187-mediated [Ca²⁺]_i uptake resulted in the up-regulation of receptor activator of NF-κB ligand (Rankl) and Sost along with increased sclerostin immunoreactivity, suggesting that [Ca²⁺]_i signaling networks may be involved in bone remodeling. In addition, A23187-treated hPDL fibroblasts also showed the suppression of osteogenic differentiation and mineralization. Our findings suggest that augmented MS-mediated [Ca²⁺]_i oscillations in hPDL fibroblasts enhance the production and release of bone regulatory signals via Rankl/Osteoprotegerin and the canonical Wnt/β-catenin pathway as an early process in tooth movement-initiated alveolar bone remodeling.-Ei Hsu Hlaing, E., Ishihara, Y., Wang, Z., Odagaki, N., Kamioka, H. Role of intracellular Ca²⁺-based mechanotransduction of human periodontal ligament fibroblasts.

Vitamin D-regulated osteocytic sclerostin and BMP2 modulate uremic extraskeletal calcification

We induced chronic kidney disease (CKD) with adenine in WT mice, mice with osteocyte-specific deletion of Cyp27b1, encoding the 25-hydroxyvitamin D 1(OH)ase [Oct-1(OH)ase-/-], and mice with global deletion of Cyp27b1 [global-1α(OH)ase-/-]; we then compared extraskeletal calcification. After adenine treatment, mice displayed increased blood urea nitrogen, decreased serum 1,25(OH)2D, and severe hyperparathyroidism. Skeletal expression of Cyp27b1 and of sclerostin and serum sclerostin all increased in WT mice but not in Oct-1α(OH)ase-/- mice or global-1α(OH)ase-/- mice. In contrast, skeletal expression of BMP2 and serum BMP2 rose in the Oct-1α(OH)ase-/- mice and in the global-1α(OH)ase-/- mice. Extraskeletal calcification occurred in muscle and blood vessels of mice with CKD and was highest in Oct-1α(OH)ase-/-mice. In vitro, recombinant sclerostin (100 ng/mL) significantly suppressed BMP2-induced osteoblastic transdifferentiation of vascular smooth muscle A7r5 cells and diminished BMP2-induced mineralization. Our study provides evidence that local osteocytic production of 1,25(OH)2D stimulates sclerostin and inhibits BMP2 production in murine CKD, thus mitigating osteoblastic transdifferentiation and mineralization of soft tissues. Increased osteocytic 1,25(OH)2D production, triggered by renal malfunction, may represent a "primary defensive response" to protect the organism from ectopic calcification by increasing sclerostin and suppressing BMP2 production.

Sclerostin levels predict cardiovascular mortality in long-term hemodialysis patients: A prospective observational cohort study

Sclerostin is a protein which is involved in bone metabolism and probably also in vessel wall function. This prospective observational cohort study evaluated the prognostic significance of sclerostin in hemodialysis (HD) patients. In total, 106 HD patients and 25 healthy controls participated in the study. HD patients were prospectively followed up for five years. Sclerostin was measured in serum using standard ELISA kits by Biomedica. Sclerostin concentrations in serum were higher in HD patients compared to the controls (89.2±40.3 pmol/l vs. 32.8±13.0 pmol/l, p<0.001). Sclerostin levels were significant for cardiovascular mortality but not for overall mortality and mortality due to infection. A higher cardiovascular risk was connected to sclerostin concentrations above the median (>84 pmol/l), HR (95 % CI): 2.577 (1.0002-10.207), p=0.04. When sclerostin was evaluated together with residual diuresis in Kaplan-Meier analysis the worst prognosis due to cardiovascular events was observed in the group with high sclerostin and zero residual diuresis compared to all other patients (p=0.007). In summary, serum sclerostin levels in HD patients were increased when compared to healthy subjects. High sclerostin levels were demonstrated as a risk factor for cardiovascular mortality. Further studies are required to clarify the pathophysiological mechanisms of sclerostin action in patients with renal failure before therapeutic measures can be established.

Effects of histone deacetylase inhibitor Scriptaid and parathyroid hormone on osteocyte functions and metabolism

Bone is a highly metabolic organ that undergoes continuous remodeling to maintain its structural integrity. During development, bones, in particular osteoblasts, rely on glucose uptake. However, the role of glucose metabolism in osteocytes is unknown. Osteocytes are terminally differentiated osteoblasts orchestrating bone modeling and remodeling. In these cells, parathyroid hormone (PTH) suppresses Sost/sclerostin expression (a potent inhibitor of bone formation) by promoting nuclear translocation of class IIa histone deacetylase (HDAC) 4 and 5 and the repression of myocyte enhancer factor 2 (MEF2) type C. Recently, Scriptaid, an HDAC complex co-repressor inhibitor, has been shown to induce MEF2 activation and exercise-like adaptation in mice. In muscles, Scriptaid disrupts the HDAC4/5 co-repressor complex, increases MEF2C function, and promotes cell respiration. We hypothesized that Scriptaid, by affecting HDAC4/5 localization and MEF2C activation, might affect osteocyte functions. Treatment of the osteocytic Ocy454-12H cells with Scriptaid increased metabolic gene expression, cell respiration, and glucose uptake. Similar effects were also seen upon treatment with PTH, suggesting that both Scriptaid and PTH can promote osteocyte metabolism. Similar to PTH, Scriptaid potently suppressed Sost expression. Silencing of HDAC5 in Ocy454-12H cells abolished Sost suppression but not glucose transporter type 4 (Glut4) up-regulation induced by Scriptaid. These results demonstrate that Scriptaid increases osteocyte respiration and glucose uptake by mechanisms independent of HDAC complex inhibition. In osteocytes, Scriptaid, similar to PTH, increases binding of HDAC5 to Mef2c with suppression of Sost but only partially increases receptor activator of NF-κB ligand (Rankl) expression, suggesting a potential bone anabolic effect.

INSL3 in the muscolo-skeletal system

Bone and skeletal muscle are currently considered a unified functional unit, showing complementary regulation at mechanical, biochemical, paracrine and metabolic levels. This functional unit undergoes a central hormonal regulation which is mainly ascribed to sex steroids and, in particular, androgens. However, recent evidence suggest that another testicular hormone lines the classical anabolic effect of testosterone on bone and muscle, the insulin-like peptide 3 (INSL3) acting on its specific receptor RXFP2. This minireview focuses on the most recent findings describing the role of INSL3/RXFP2 axis on the muscolo-skeletal system, from the mechanistic insights to the phenotypic consequences. Pathophysiological and therapeutic widenings deriving from available data are also discussed.

Osteoanabolic and dual action drugs

Teriparatide (TPTD) and abaloparatide (ABL) are the only osteoanabolic drugs available, at this time, for treatment of osteoporosis. TPTD is a 34-amino acid fragment that is identical in its primary sequence to the 34 amino acids of full-length human parathyroid hormone [hPTH(1-84)]. ABL is identical to parathyroid hormone-related peptide (PTHrP) through the first 22 residues with significantly different amino acids inserted thereafter, between residues 22 and 34. The osteoanabolic actions of PTH are due directly to its effects on cells of the osteoblast lineage and indirectly by stimulating IGF-I synthesis and suppressing sclerostin and associated enhancement of Wnt signalling. Both TPTD and ABL are ligands that bind to and activate the PTH receptor type 1 (PTHR1) receptor but they appear to do so differently: ABL favours the transient, more anabolic configuration of the receptor. Both TPTD and ABL reduce the risk of vertebral fractures and non-vertebral fractures. Both drugs are administered for a maximum of 24 months, and should be followed by an antiresorptive agent to maintain gains in bone mineral density (BMD). Romosozumab, a monoclonal antibody that binds to and inhibits sclerostin, appears to have dual actions by stimulating bone formation and reducing bone resorption. In the pivotal clinical trial, romosozumab, administered as a 210 mg monthly subcutaneous dose, significantly reduced new vertebral fractures and in a subsequent study reduced both vertebral and non-vertebral fractures.

Wnt Antagonists in Hematopoietic and Immune Cell Fate: Implications for Osteoporosis Therapies

PURPOSE OF REVIEW

We reviewed the current literature on the roles of the Wnt antagonists sclerostin (Sost) and sclerostin-containing domain protein 1 (Sostdc1) on bone homeostasis, the relationship of the hypoxia-inducible factor (Hif) and von Hippel-Lindau (Vhl) pathways on Sost expression, and how changes in bone induced by depletion of Sost, Sostdc1, and Vhl affect hematopoietic cells.

RECENT FINDINGS

B cell development is adversely affected in Sost-knockout mice and is more severely affected in Vhl-knockout mice. Inflammation in the Sost^-/- bone microenvironment could alter hematopoietic stem cell behavior. Sostdc1^-/- mice display defects in natural killer cell development and cytotoxicity. Depletion of Sost and Sostdc1 have effects on immune cell function that warrant investigation in patients receiving Wnt antagonist-depleting therapies for treatment of bone diseases. Additional clinical applications for manipulation of Wnt antagonists include cancer immunotherapies, stem cell transplantation, and directed differentiation to immune lineages.

Sclerostin Modulation Holds Promise for Dental Indications

Sclerostin modulation is a novel therapeutic bone regulation strategy. The anti-sclerostin drugs, proposed in medicine for skeletal bone loss may be developed for jaw bone indications in dentistry. Alveolar bone responsible for housing dentition share common bone remodeling mechanisms with skeletal bone. Manipulating alveolar bone turnover can be used as a strategy to treat diseases such as periodontitis, where large bone defects from disease are a surgical treatment challenge and to control tooth position in orthodontic treatment, where moving teeth through bone in the treatment goal. Developing such therapeutics for dentistry is a future line for research and therapy. Furthermore, it underscores the interprofessional relationship that is the future of healthcare.

Clinical advantages and disadvantages of anabolic bone therapies targeting the WNT pathway

The WNT signalling pathway is a key regulator of bone metabolism, particularly bone formation, which has helped to define the role of osteocytes - the most abundant bone cells - as orchestrators of bone remodelling. Several molecules involved in the control of the WNT signalling pathway have been identified as potential targets for the development of bone-building therapeutics for patients with osteoporosis. Several of these molecules have been investigated in animal models, but only inhibitors of sclerostin (which is produced by osteocytes) have been investigated in phase III clinical studies. Here, we review the rationale for these developments and the specificity and potential off-target actions of WNT-based therapeutics. We also describe the available preclinical and clinical studies and discuss the benefits and risks of using sclerostin inhibitors for the management of patients with osteoporosis.

Inhibitory Effects of Human Primary Intervertebral Disc Cells on Human Primary Osteoblasts in a Co-Culture System

Spinal fusion is a common surgical procedure to address a range of spinal pathologies, like damaged or degenerated discs. After the removal of the intervertebral disc (IVD), a structural spacer is positioned followed by internal fixation, and fusion of the degenerated segment by natural bone growth. Due to their osteoinductive properties, bone morphogenetic proteins (BMP) are applied to promote spinal fusion. Although spinal fusion is successful in most patients, the rates of non-unions after lumbar spine fusion range from 5% to 35%. Clinical observations and recent studies indicate, that the incomplete removal of disc tissue might lead to failure of spinal fusion. Yet, it is still unknown if a secretion of BMP antagonists in intervertebral disc (IVD) cells could be the reason of inhibition in bone formation. In this study, we co-cultured human primary osteoblasts (OB) and IVD cells i.e., nucleus pulposus (NPC), annulus fibrosus (AFC) and cartilaginous endplate cells (CEPC), to test the possible inhibitory effect from IVD cells on OB. Although we could see a trend in lower matrix mineralization in OB co-cultured with IVD cells, results of alkaline phosphatase (ALP) activity and gene expression of major bone genes were inconclusive. However, in NPC, AFC and CEPC beads, an up-regulation of several BMP antagonist genes could be detected. Despite being able to show several indicators for an inhibition of osteoinductive effects due to IVD cells, the reasons for pseudarthrosis after spinal fusion remain unclear.

Targeted inhibition of sclerostin for post-menopausal osteoporosis therapy: A critical assessment of the mechanism of action

Promising news in the treatment of osteoporosis is that sequestering sclerostin from circulation with antibodies stimulates robust bone formation. Pre-clinical studies on rodents and monkeys have confirmed that treatment with anti-sclerostin monoclonal antibody (Scl-Ab) increases bone mass, improves bone strength and enhances fracture repair. Clinical trials show that bone gain (anabolic effect) is transient and are primarily at central (spine and hips) than peripheral (wrist) sites. Interestingly Scl-Ab also inhibited bone resorption. Thus Scl-Ab is being regarded as the pharmacologic agent with dual properties - stimulating bone formation and decreasing bone resorption. Sclerostin neutralization transiently increases bone formation markers in post-menopausal women and like parathyroid hormone (PTH) activates osteoblasts and lining cells resulting in bone anabolic effect. However, unlike PTH, sclerostin antibody also decreases bone resorption (anti-catabolic). Although, the U.S. Food and Drug Administration have accepted the Biologics License Application for one of the monoclonal antibodies against sclerostin (romosozumab) for review, many questions remain before romosozumab can be introduced as a skeletal anabolic agent to clinical practice. For example, neutralizing sclerostin alters calcium homeostasis and increases PTH. In addition, sclerostin depletion in preclinical studies has been reported to severely compromises B cell depletion in bone marrow. We have reviewed the currently available evidences that support the use of sclerostin antibody in treating osteoporosis and compare its efficacy and mechanism of action with the currently available anabolic drug, human PTH.

Bariatric Roux-En-Y Gastric Bypass Surgery: Adipocyte Proteins Involved in Increased Bone Remodeling in Humans

PURPOSE

Bariatric surgery has been associated with bone remodeling changes. The action of adipokines on the expression of receptor activator of nuclear factor kappa β ligand (RANKL) and osteoprotegerin (OPG) and on an increase in sclerostin could be related to these changes.

MATERIALS AND METHODS

This study aimed to assess the repercussions of weight loss, fat mass (FM), and fat-free mass (FFM) loss and biochemical and hormonal changes on bone remodeling markers after Roux-en-Y gastric bypass (RYGB). Anthropometric data, parathyroid hormone (PTH), bone-specific alkaline phosphatase (BSAP), collagen type 1 C-telopeptide (CTX), 25-hydroxy vitamin D (25-OH-VitD), leptin, adiponectin, RANKL, OPG, and sclerostin of 30 menstruating women were measured preoperatively (Pre), and 3, 12, and 24 months (m) after RYGB.

RESULTS

Leptin (34.4 (14.7; 51.9) vs. 22.5 (1.9; 52.7) ng/mL) and OPG (3.6 (1.1; 11.5) vs. 3.4 (1.5; 6) pmol/L) decreased, and adiponectin (7.4 (1.7; 18.4) vs. 13.8 (3.0; 34.6) μg/mL), CTX (0.2 (0.1; 2.2) vs. 0.6 (0.4; 6.0) ng/mL), RANKL (0.1 (0.0; 0.5) vs. 0.3 (0.0; 2.0) pmol/L), and sclerostin (21.7 (3.2; 75.1) vs. 34.8 (6.4; 80.5) pmol/L) increased after 3 m. BSAP increased after 12 m (10.1 (5.4; 18.9) vs. 13.9 (6.9; 30.2) μg/mL) (p < 0.005). CTX correlated positively with adiponectin at 24 m and inversely with leptin Pre; OPG at 3 m; weight, FM, FFM, and leptin at 24 m. RANKL correlated directly with weight at 3 m. Sclerostin correlated inversely with weight Pre and FM at 3 m. BSAP correlated negatively with 25-OH-VitD at 12 m, and positively with PTH at 24 m.

CONCLUSIONS

RYGB induced weight loss, and biochemical, hormonal, and body composition changes are associated with higher bone remodeling.

Interrelationship of canonical and non-canonical Wnt signalling pathways in chronic metabolic diseases

Chronic diseases account for approximately 45% of all deaths in developed countries and are particularly prevalent in countries with the most sophisticated and robust public health systems. Chronic metabolic diseases, specifically lifestyle-related diseases pertaining to diet and exercise, continue to be difficult to treat clinically. The most prevalent of these chronic metabolic diseases include obesity, diabetes, non-alcoholic fatty liver disease, chronic kidney disease and cardiovascular disease and will be the focus of this review. Wnt proteins are highly conserved glycoproteins best known for their role in development and homeostasis of tissues. Given the importance of Wnt signalling in homeostasis, aberrant Wnt signalling likely regulates metabolic processes and may contribute to the development of chronic metabolic diseases. Expression of Wnt proteins and dysfunctional Wnt signalling has been reported in multiple chronic diseases. It is interesting to speculate about an interrelationship between the Wnt signalling pathways as a potential pathological mechanism in chronic metabolic diseases. The aim of this review is to summarize reported findings on the contrasting roles of Wnt signalling in lifestyle-related chronic metabolic diseases; specifically, the contribution of Wnt signalling to lipid accumulation, fibrosis and chronic low-grade inflammation.

The sclerostin-neutralizing antibody AbD09097 recognizes an epitope adjacent to sclerostin's binding site for the Wnt co-receptor LRP6

The glycoprotein sclerostin has been identified as a negative regulator of bone growth. It exerts its function by interacting with the Wnt co-receptor LRP5/6, blocks the binding of Wnt factors and thereby inhibits Wnt signalling. Neutralizing anti-sclerostin antibodies are able to restore Wnt activity and enhance bone growth thereby presenting a new osteoanabolic therapy approach for diseases such as osteoporosis. We have generated various Fab antibodies against human and murine sclerostin using a phage display set-up. Biochemical analyses have identified one Fab developed against murine sclerostin, AbD09097 that efficiently neutralizes sclerostin's Wnt inhibitory activity. In vitro interaction analysis using sclerostin variants revealed that this neutralizing Fab binds to sclerostin's flexible second loop, which has been shown to harbour the LRP5/6 binding motif. Affinity maturation was then applied to AbD09097, providing a set of improved neutralizing Fab antibodies which particularly bind human sclerostin with enhanced affinity. Determining the crystal structure of AbD09097 provides first insights into how this antibody might recognize and neutralize sclerostin. Together with the structure-function relationship derived from affinity maturation these new data will foster the rational design of new and highly efficient anti-sclerostin antibodies for the therapy of bone loss diseases such as osteoporosis.

Loss of mechanosensitive sclerostin may accelerate cranial bone growth and regeneration

OBJECTIVE

Cranial defects can result from trauma, infection, congenital malformations, and iatrogenic causes and represent a surgical challenge. The current standard of care is cranioplasty, with either autologous or allogeneic material. In either case, the intrinsic vascularity of the surrounding tissues allows for bone healing. The objective of this study was to determine if mechanotransductive gene manipulation would yield non-weight-bearing bone regeneration in a critical size calvarial defect in mice.

METHODS

A mouse model of Sost deletion in Sost knockout (KO) mice was created in which the osteocytes do not express sclerostin. A critical size calvarial defect (4 mm in diameter) was surgically created in the parietal bone in 8-week-old wild-type (n = 8) and Sost KO (n = 8) male mice. The defects were left undisturbed (no implant or scaffold) to simulate a traumatic calvariectomy model. Eight weeks later, the animals were examined at necropsy by planimetry, histological analysis of new bone growth, and micro-CT scanning of bone thickness.

RESULTS

Defects created in wild-type mice did not fill with bone over the study period of 2 months. Genetic downregulation of sclerostin yielded animals that were able to regenerate 40% of the initial critical size defect area 8 weeks after surgery. A thin layer of bone covered a significant portion of the original defect in all Sost KO animals. A statistically significant increase in bone volume (p < 0.05) was measured in Sost KO mice using radiodensitometric analysis. Immunohistochemical analysis also confirmed that this bone regeneration occurred through the Wnt pathway and originated from the edge of the defect; BMP signaling did not appear to be affected by sclerostin.

CONCLUSIONS

Mechanical loading is an important mechanism of bone formation in the cranial skeleton and is poorly understood. This is partially due to the fact that it is difficult to load bone in the craniomaxillofacial skeleton. This study suggests that modulation of the Wnt pathway, as is able to be done with monoclonal antibodies, is a potentially efficacious method for bone regeneration that requires further study.