GSK-3β inhibition suppresses instability-induced osteolysis by a dual action on osteoblast and osteoclast differentiation

Glycogen Synthase Kinase-3 Beta (GSK3β) as a Potential Drug Target in Regulating Osteoclastogenesis: An Updated Review on Current Evidence

Glycogen synthase kinase 3-beta (GSK3β) is a highly conserved protein kinase originally involved in glucose metabolism, insulin activity, and energy homeostasis. Recent scientific evidence demonstrated the significant role of GSK3β in regulating bone remodelling through involvement in multiple signalling networks. Specifically, the inhibition of GSK3β enhances the conversion of osteoclast progenitors into mature osteoclasts. GSK3β is recognised as a pivotal regulator for the receptor activator of nuclear factor-kappa B (RANK)/receptor activator of nuclear factor-kappa B ligand (RANKL)/osteoprotegerin (OPG), phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT), nuclear factor-kappa B (NF-κB), nuclear factor-erythroid 2-related factor 2 (NRF2)/Kelch-like ECH-associated protein 1 (KEAP1), canonical Wnt/beta (β)-catenin, and protein kinase C (PKC) signalling pathways during osteoclastogenesis. Conversely, the inhibition of GSK3β has been shown to prevent bone loss in animal models with complex physiology, suggesting that the role of GSK3β may be more significant in bone formation than bone resorption. Divergent findings have been reported regarding the efficacy of GSK3β inhibitors as bone-protecting agents. Some studies demonstrated that GSK3β inhibitors reduced osteoclast formation, while one study indicated an increase in osteoclast formation in RANKL-stimulated bone marrow macrophages (BMMs). Given the discrepancies observed in the accumulated evidence, further research is warranted, particularly regarding the use of GSK3β silencing or overexpression models. Such efforts will provide valuable insights into the direct impact of GSK3β on osteoclastogenesis and bone resorption.

Role of Adipose Tissue Hormones in Pathogenesis of Cryptoglandular Anal Fistula

The cryptoglandular perianal fistula is a common benign anorectal disorder that is managed mainly with surgery and in some cases may be an extremely challenging condition. Perianal fistulas are often characterized by significantly decreased patient quality of life. Lack of fully recognized pathogenesis of this disease makes it difficult to treat it properly. Recently, adipose tissue hormones have been proposed to play a role in the genesis of cryptoglandular anal fistulas. The expression of adipose tissue hormones and epithelial-to-mesenchymal transition (EMT) factors were characterized based on 30 samples from simple fistulas and 30 samples from complex cryptoglandular perianal fistulas harvested during surgery. Tissue levels of leptin, resistin, MMP2, and MMP9 were significantly elevated in patients who underwent operations due to complex cryptoglandular perianal fistulas compared to patients with simple fistulas. Adiponectin and E-cadherin were significantly lowered in samples from complex perianal fistulas in comparison to simple fistulas. A negative correlation between leptin and E-cadherin levels was observed. Resistin and MMP2 levels, as well as adiponectin and E-cadherin levels, were positively correlated. Complex perianal cryptoglandular fistulas have a reduced level of the anti-inflammatory adipokine adiponectin and have an increase in the levels of proinflammatory resistin and leptin. Abnormal secretion of these adipokines may affect the integrity of the EMT in the fistula tract. E-cadherin, MMP2, and MMP9 expression levels were shifted in patients with more advanced and complex perianal fistulas. Our results supporting the idea of using mesenchymal stem cells in the treatment of cryptoglandular perianal fistulas seem reasonable, but further studies are warranted.

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.

Titanium particles inhibit bone marrow mesenchymal stem cell osteogenic differentiation through the MAPK signaling pathway

Metallic implants have great application in clinical orthopedics. Implants wear out in vivo due to long-term mechanical loading. The formation of wear debris is one of the long-term complications of prosthesis. In the case of artificial joint replacement in particular, aseptic loosening is the most common reason for secondary revision surgery. Previous studies suggested that wear debris caused aseptic loosening mainly by promoting osteolysis around the prosthesis. In this study, titanium particles, the most commonly used particles in clinical practice, were selected to simulate wear debris and explore the influence of titanium particles on osteogenic differentiation of mesenchymal stem cells. Our results show that titanium particles can significantly inhibit osteogenic differentiation in a dose-dependent manner. While engaged in preliminary exploration of the underlying mechanisms, we found that titanium particles significantly affect phosphorylation of ERK1/2, a key component of MAPK signaling. This suggests that the MAPK signaling pathway is involved in the inhibition of osteogenic differentiation by titanium particles.

Strategic outline of interventions targeting extracellular matrix for promoting healthy longevity

The extracellular matrix (ECM), composed of interlinked proteins outside of cells, is an important component of the human body that helps maintain tissue architecture and cellular homeostasis. As people age, the ECM undergoes changes that can lead to age-related morbidity and mortality. Despite its importance, ECM aging remains understudied in the field of geroscience. In this review, we discuss the core concepts of ECM integrity, outline the age-related challenges and subsequent pathologies and diseases, summarize diagnostic methods detecting a faulty ECM, and provide strategies targeting ECM homeostasis. To conceptualize this, we built a technology research tree to hierarchically visualize possible research sequences for studying ECM aging. This strategic framework will hopefully facilitate the development of future research on interventions to restore ECM integrity, which could potentially lead to the development of new drugs or therapeutic interventions promoting health during aging.

Methanolic extract of O.umbellata L. exhibits anti-osteoporotic effect via promoting osteoblast proliferation in MG-63 cells and inhibiting osteoclastogenesis in RANKL-stimulated RAW 264.7 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Oldenlandia umbellataL., belonging to the Rubiaceae family, is an annual plant possessing anti-inflammatory and antipyretic, anti-nociceptive, anti-bacterial, anti-helminthic, antioxidant and hepatoprotective activities and used in traditional medicine to treat inflammation and respiratory diseases.

AIM OF THE STUDY

The present study aims to evaluate the anti-osteoporotic effect of Methanolic extract of O.umbellata in MG-63 cells and RANKL-stimulated RAW 264.7 cells.

MATERIALS AND METHODS

The methanolic extract from the aerial parts of O.umbellata was subjected to metabolite profiling. The anti-osteoporotic effect of MOU was assessed in MG-63 cells and RANKL-stimulated RAW 264.7 cells. In MG-63 cells, the proliferative effect of MOU was evaluated using MTT assay, ALP assay, Alizarin red staining, ELISA and western blot. Similarly, the anti-osteoclastogenic effect of MOU was assessed in RANKL-stimulated RAW 264.7 cells via MTT, TRAP staining and western blot.

RESULTS

LC-MS metabolite profiling showed the presence of 59 phytoconstituents including scandoside, scandoside methyl ester, deacetylasperuloside, asperulosidic acid, and cedrelopsin in MOU. In MG-63 cells, MOU has increased the proliferation of osteoblast cells and ALP activity, thereby increasing bone mineralization. ELISA results showed increased levels of osteogenic markers such as osteocalcin and osteopontin in the culture media. Western blot analysis showed inhibition of GSK3β protein expression and increased the expression levels of β-catenin, Runx-2, col 1 and osterix, promoting osteoblast differentiation. In RANKL-stimulated RAW 264.7 cells, MOU did not elicit any significant cytotoxicity; instead, it suppressed the osteoclastogenesis reducing the osteoclast number. MOU has reduced TRAP activity in a dose-dependent manner. MOU inhibited the TRAF6, NFATc1, c-Jun, C-fos and cathepsin K expression, thereby inhibiting osteoclast formation.

CONCLUSION

In conclusion, MOU promoted osteoblast differentiation via inhibiting GSK3β and activating Wnt/β catenin signalling and its transcription factors, including β catenin, Runx2 and Osterix. Similarly, MOU inhibited osteoclast formation by inhibiting the expression of TRAF6, NFATc1, c-Jun, C-fos and cathepsin K in RANK-RANKL signalling. Finally, it can be emphasised that O.umbellata is a potential source of therapeutic leads for the treatment of osteoporosis.

Sec-O-Glucosylhamaudol Inhibits RANKL-Induced Osteoclastogenesis by Repressing 5-LO and AKT/GSK3β Signaling

Sec-O-glucosylhamaudol (SOG), an active flavonoid compound derived from the root of Saposhnikovia divaricata (Turcz. ex Ledeb.) Schischk., exhibits analgesic, anti-inflammatory, and high 5-lipoxygenase (5-LO) inhibitory effects. However, its effect on osteoclastogenesis was unclear. We demonstrated that SOG markedly attenuated RANKL-induced osteoclast formation, F-actin ring formation, and mineral resorption by reducing the induction of key transcription factors NFATc1, c-Fos, and their target genes such as TRAP, CTSK, and DC-STAMP during osteoclastogenesis. Western blotting showed that SOG significantly inhibited the phosphorylation of AKT and GSK3β at the middle–late stage of osteoclastogenesis without altering calcineurin catalytic subunit protein phosphatase-2β-Aα expression. Moreover, GSK3β inhibitor SB415286 partially reversed SOG-induced inhibition of osteoclastogenesis, suggesting that SOG inhibits RANKL-induced osteoclastogenesis by activating GSK3β, at least in part. 5-LO gene silencing by small interfering RNA in mouse bone marrow macrophages markedly reduced RANKL-induced osteoclastogenesis by inhibiting NFATc1. However, it did not affect the phosphorylation of AKT or GSK3β, indicating that SOG exerts its inhibitory effects on osteoclastogenesis by suppressing both the independent 5-LO pathway and AKT-mediated GSK3β inactivation. In support of this, SOG significantly improved bone destruction in a lipopolysaccharide-induced mouse model of bone loss. Taken together, these results suggest a potential therapeutic effect for SOG on osteoclast-related bone lysis disease.

Bioactive coatings with anti-osteoclast therapeutic agents for bone implants: Enhanced compliance and prolonged implant life

The use of therapeutic agents that inhibit bone resorption is crucial to prolong implant life, delay revision surgery, and reduce the burden on the healthcare system. These therapeutic agents include bisphosphonates, various nucleic acids, statins, proteins, and protein complexes. Their use in systemic treatment has several drawbacks, such as side effects and insufficient efficacy in terms of concentration, which can be eliminated by local treatment. This review focuses on the incorporation of osteoclast inhibitors (antiresorptive agents) into bioactive coatings for bone implants. The ability of bioactive coatings as systems for local delivery of antiresorptive agents to achieve optimal loading of the bioactive coating and its release is described in detail. Various parameters such as the suitable concentrations, release times, and the effects of the antiresorptive agents on nearby cells or bone tissue are discussed. However, further research is needed to support the optimization of the implant, as this will enable subsequent personalized design of the coating in terms of the design and selection of the coating material, the choice of an antiresorptive agent and its amount in the coating. In addition, therapeutic agents that have not yet been incorporated into bioactive coatings but appear promising are also mentioned. From this work, it can be concluded that therapeutic agents contribute to the biocompatibility of the bioactive coating by enhancing its beneficial properties.

Increasing Odontoblast-like Differentiation from Dental Pulp Stem Cells through Increase of β-Catenin/p-GSK-3β Expression by Low-Frequency Electromagnetic Field

Odontoblasts produce proteins that form the dentinal extracellular matrix, which can protect the dental pulp from external stimuli and is required for tooth regeneration. This study showed that a pulsed electromagnetic field (PEMF) can regulate cell metabolism and induce cell differentiation. This study determined the frequency of PEMF that is effective for odontoblast differentiation. Human dental pulp stem cells (hDPSCs) were cultured in odontoblast differentiation medium containing dexamethasone, BMP2, TGF-β1, and FGF-2, and then exposed to 10 mT intensity of PEMF at 40, 60, 70, and 150 Hz for 15 min/day. The MTT assay, LDH assay, flow cytometry, protein and gene expression, and immunofluorescence were performed to check if hDPSCs differentiated into odontoblast-like cells. The hDPSCs showed frequency-dependent differences in protein and gene expression. The mesenchymal stem cell markers were reduced to a greater extent at 60 and 70 Hz than at other frequencies, and odontoblast-related markers, particularly β-catenin, p-GSK-3β, and p-p38, were increased at 60 and 70 Hz. Exposure to 10 mT intensity of PEMF at 70 Hz influenced the differentiation of hDPSCs considerably. Taken together, PEMF treatment can promote differentiation of hDPSCs into odontoblast-like cells by increasing p-GSK-3β and β-catenin expression.

Recent Progresses in the Treatment of Osteoporosis

Osteoporosis (OP) is a chronic bone disease characterized by aberrant microstructure and macrostructure of bone, leading to reduced bone mass and increased risk of fragile fractures. Anti-resorptive drugs, especially, bisphosphonates, are currently the treatment of choice in most developing countries. However, they do have limitations and adverse effects, which, to some extent, helped the development of anabolic drugs such as teriparatide and romosozumab. In patients with high or very high risk for fracture, sequential or combined therapies may be considered with the initial drugs being anabolic agents. Great endeavors have been made to find next generation drugs with maximal efficacy and minimal toxicity, and improved understanding of the role of different signaling pathways and their crosstalk in the pathogenesis of OP may help achieve this goal. Our review focused on recent progress with regards to the drug development by modification of Wnt pathway, while other pathways/molecules were also discussed briefly. In addition, new observations made in recent years in bone biology were summarized and discussed for the treatment of OP.

Bone Homeostasis and Gut Microbial-Dependent Signaling Pathways

Although research on the osteal signaling pathway has progressed, understanding of gut microbial-dependent signaling pathways for metabolic and immune bone homeostasis remains elusive. In recent years, the study of gut microbiota has shed light on our understanding of bone homeostasis. Here, we review microbiota-mediated gut-bone crosstalk via bone morphogenetic protein/SMADs, Wnt and OPG/receptor activator of nuclear factor-kappa B ligand signaling pathways in direct (translocation) and indirect (metabolite) manners. The mechanisms underlying gut microbiota involvement in these signaling pathways are relevant in immune responses, secretion of hormones, fate of osteoblasts and osteoclasts and absorption of calcium. Collectively, we propose a signaling network for maintaining a dynamic homeostasis between the skeletal system and the gut ecosystem. Additionally, the role of gut microbial improvement by dietary intervention in osteal signaling pathways has also been elucidated. This review provides unique resources from the gut microbial perspective for the discovery of new strategies for further improving treatment of bone diseases by increasing the abundance of targeted gut microbiota.

Astragalus polysaccharide attenuates LPS-related inflammatory osteolysis by suppressing osteoclastogenesis by reducing the MAPK signalling pathway

Bacterial products can stimulate inflammatory reaction and activate immune cells to enhance the production of inflammatory cytokines, and finally promote osteoclasts recruitment and activity, leading to bone destruction. Unfortunately, effective preventive and treatment measures for inflammatory osteolysis are limited and usually confuse the orthopedist. Astragalus polysaccharide (APS), the main extractive of Astragali Radix, has been widely used for treating inflammatory diseases. In the current study, in vitro and in vivo experimental results demonstrated that APS notably inhibited osteoclast formation and differentiation dose-dependently. Moreover, we found that APS down-regulated RANKL-related osteoclastogenesis and levels of osteoclast marker genes, such as NFATC1, TRAP, c-FOS and cathepsin K. Further underlying mechanism investigation revealed that APS attenuated activity of MAPK signalling pathways (eg ERK, JNK and p38) and ROS production induced by RANKL. Additionally, APS was also found to suppress LPS-related inflammatory osteolysis by decreasing inflammatory factors' production in vivo. Overall, our findings demonstrate that APS effectively down-regulates inflammatory osteolysis due to osteoclast differentiation and has the potential to become an effective treatment of the disorders associated with osteoclast.

Inhibitory effect of acetyl-11-keto-β-boswellic acid on titanium particle-induced bone loss by abrogating osteoclast formation and downregulating the ERK signaling pathway

Wear debris-induced osteoclast accumulation around implants plays a crucial role during the progression of periprosthetic osteolysis (PPO). We have confirmed that acetyl-11-keto-β-boswellic acid (AKBA) promotes bone formation and protects against particle-induced bone destruction in vivo. However, the effect of AKBA on titanium-induced bone resorption is unknown. In this study, we detected the inhibitory effect of AKBA on titanium-induced bone erosion in vivo and used RAW264.7 cells and bone marrow macrophages (BMMs) to investigate the effect and underlying mechanism of AKBA on the differentiation and resorptive function of osteoclasts. Our findings revealed that AKBA inhibited particle-induced bone loss and osteoclast formation in vivo. Furthermore, AKBA exerted inhibitory effects on RANKL-induced osteoclastogenesis, osteoclastic ring-dependent resorption and the expression of osteoclast marker genes via the ERK signaling pathway in vitro. Our data further established the protective effect of AKBA on titanium particle-induced bone erosion from a new perspective of bone erosion prevention, strongly confirming that AKBA is an appropriate agent for protection against PPO.

Development of an immunogenomic landscape for the competing endogenous RNAs network of peri-implantitis

BACKGROUND

Peri-implantitis is an inflammation that occurs around the implant, resulting in varying degrees of inflammatory damage to the soft and hard tissues. The characteristic criterion is the loss of the supporting bone in an inflammatory environment. However, the specific mechanisms and biomarkers involved in peri-implantitis remain to be further studied. Recently, competing endogenous RNAs (ceRNA) and immune microenvironment have been found to play a more important role in the inflammatory process. In our study, we analyzed the expression of immune related microRNAs (miRNAs), long noncoding RNAs (lncRNAs) and message RNAs (mRNAs) in peri-implantitis by analyzing GSE33774 and GSE57631.

METHODS

In this study, we explored the expression profile data of immune-related lncRNAs, miRNAs and mRNAs, and constructed immune-related ceRNA network involved in the pathogenesis of peri-implantitis. In addition, the CIBERSORT was used to evaluate the content of immune cells in normal tissues and peri-implantitis to detect the immune microenvironment of peri-implantitis.

RESULTS

In the analysis, 14 DElncRNAs, 16 DEmiRNAs, and 18 DEmRNAs were used to establish an immune related ceRNA network and the immune infiltration patterns associated with peri-implantitis was discovered. Through the mutual verification of the two datasets, we found that GSK3B and miR-1297 may have important significance in the immune microenvironment and pathogenesis of peri-implantitis and GSK3B was closely related to four types of immune cells, especially with the highest correlation with resting mast cells (P = 0.0003).

CONCLUSIONS

Through immune-related ceRNA network, immune-related genes (IRGs) and immune cell infiltration can further comprehensively understand the pathogenesis of peri-implantitis, which built up an immunogenomic landscape with clinical significance for peri-implantitis.

The Effects of Biomaterial Implant Wear Debris on Osteoblasts

Aseptic loosening subsequent to periprosthetic osteolysis is the leading cause for the revision of arthroplasty failure. The biological response of macrophages to wear debris has been well established, however, the equilibrium of bone remodeling is not only dictated by osteoclastic bone resorption but also by osteoblast-mediated bone formation. Increasing evidence shows that wear debris significantly impair osteoblastic physiology and subsequent bone formation. In the present review, we update the current state of knowledge regarding the effect of biomaterial implant wear debris on osteoblasts. The interaction of osteoblasts with osteoclasts and macrophages under wear debris challenge, and potential treatment options targeting osteoblasts are also presented.

Local Wnt3a treatment restores bone regeneration in large osseous defects after surgical debridement of osteomyelitis

Impaired bone homeostasis caused by osteomyelitis provokes serious variations in the bone remodeling process, thereby involving multiple inflammatory cytokines to activate bone healing. We have previously established a mouse model for post-traumatic osteomyelitis and studied bone regeneration after sufficient debridement. Moreover, we could further characterize the postinfectious inflammatory state of bony defects after debridement with elevated osteoclasts and decreased bone formation despite the absence of bacteria. In this study, we investigated the positive effects of Wnt-pathway modulation on bone regeneration in our previous established mouse model. This was achieved by local application of Wnt3a, a recombinant activator of the canonical Wnt-pathway. Application of Wnt3a could enhance new bone formation, which was verified by histological and μ-CT analysis. Moreover, histology and western blots revealed enhanced osteoblastogenesis and downregulated osteoclasts in a RANKL-dependent manner. Further analysis of Wnt-pathway showed downregulation after bone infections were reconstituted by application of Wnt3a. Interestingly, Wnt-inhibitory proteins Dickkopf 1 (DKK1), sclerostin, and secreted frizzled protein 1 (sFRP1) were upregulated simultaneously to Wnt-pathway activation, indicating a negative feedback for active form of Beta-catenin. In this study, we could demonstrate enhanced bone formation in defects caused by post-traumatic osteomyelitis after Wnt3a application. KEY MESSAGES: Osteomyelitis decreases bone regeneration Wnt3a restores bone healing after infection Canonical Wnt-pathway activation with negative feedback.

The Genetic Variations Associated With Time to Aseptic Loosening After Total Joint Arthroplasty

BACKGROUND

Total joint arthroplasty (TJA) is one of the most frequent surgical procedures performed in modern hospitals, and aseptic loosening is the most common indication for revision surgeries. We conducted a systemic exploration of potential genetic determinants for early aseptic loosening.

METHODS

Data from 423 patients undergoing TJA were collected and analyzed. Three analytical groups were formed based on joint arthroplasty status. Group 1 were TJA patients without symptoms of aseptic loosening of at least 1 year, group 2 were patients with primary TJA, and group 3 were patients receiving revision surgery because of aseptic loosening. Genome-wide genotyping comparing genotype frequencies between patients with and without aseptic loosening (group 3 vs groups 1 and 2) was conducted. A case-control association analysis and linear modeling were applied to identify the impact of the identified genes on implant survival with time to the revision as an outcome measure.

RESULTS

We identified 52 single-nucleotide polymorphisms (SNPs) with a genome-wide suggestive P value less than 10^-5 to be associated with the implant loosening. The most remarkable odds ratios (OR) were found with the variations in the IFIT2/IFIT3 (OR, 21.6), CERK (OR, 12.6), and PAPPA (OR, 14.0) genes. Variations in the genotypes of 4 SNPs-rs115871127, rs16823835, rs13275667, and rs2514486-predicted variability in the time to aseptic loosening. The time to aseptic loosening varied from 8 to 16 years depending on the genotype, indicating a substantial effect of genetic variance.

CONCLUSION

Development of the aseptic loosening is associated with several genetic variations and we identified at least 4 SNPs with a significant effect on the time for loosening. These data could help to develop a personalized approach for TJA and loosening management.

Mechanical instability induces osteoclast differentiation independent of the presence of a fibrous tissue interface and osteocyte apoptosis in a rat model for aseptic loosening

Background and purpose - Insufficient initial fixation or early micromotion of an implant is associated with a thin layer of fibrous tissue at the peri-implant interface. It is unknown if bone loss is induced by the fibrous tissue interface acting as an active biological membrane, or as a membrane that will produce supraphysiologic fluid flow conditions during gait, which activates the mechanosensitive osteocytes to mediate osteoclast differentiation. We investigated whether mechanically induced osteolysis is dependent on the fibrous tissue interface as a biologically active scaffold, or if it merely acts as a conduit for fluid flow, affecting the mechanosensitive osteocytes in the peri-prosthetic bone.Methods - Using a rat model of mechanically instability-induced aseptic loosening, we assessed whether the induction of osteoclast differentiation was dependent on the presence of a peri-implant fibrous interface. We analyzed the amount of osteoclast differentiation, osteocyte apoptosis, pro-resorptive cytokine expression and bone loss using immunohistochemistry, mRNA expression and micro-CT.Results - Osteoclast differentiation and bone loss were induced by mechanical instability but were not affected by the presence of the fibrous tissue membrane or associated with osteocyte apoptosis. There was no increased mRNA expression of any of the cytokines in the fibrous tissue membrane compared with the peri-implant bone.Interpretation - Our data show that the fibrous tissue membrane in the interface plays a minor role in inducing bone loss. This indicates that the peri-implant bone adjacent to loose bone implants might play an important role for osteoclast differentiation.

Mechanically Induced Periprosthetic Osteolysis: A Systematic Review

BACKGROUND

Peri-prosthetic bone loss can result from chemical, biological, and mechanical factors. Mechanical stimulation via fluid pressure and flow at the bone-implant interface may be a significant cause. Evidence supporting mechanically induced osteolysis continues to grow, but there is no synthesis of published clinical and basic science data.

QUESTIONS/PURPOSES

We sought to review the literature on two questions: (1) What published evidence supports the concept of mechanically induced osteolysis? (2) What is the proposed mechanism of mechanically induced osteolysis, and does it differ from that of particle-induced osteolysis?

METHODS

A systematic review was performed of the PubMed and Web of Science databases. Additional relevant articles were recommended by the senior authors based on their expert opinion. Abstracts were reviewed and the manuscripts pertaining to the study questions were read in full. Studies showing support of mechanically induced osteolysis were quantified and findings summarized.

RESULTS

We identified 49 articles of experimental design supporting the hypothesis that mechanical stimulation of peri-prosthetic bone from fluid pressure and flow can induce osteolysis. While the molecular mechanisms may overlap with those implicated in particle-induced osteolysis, mechanically induced osteolysis appears to be mediated by distinct and parallel pathways.

CONCLUSIONS

The role of mechanical stimuli is increasingly recognized in the pathogenesis of peri-prosthetic osteolysis. Current research aims to elucidate the molecular mechanisms to better target therapeutic interventions.

Rehmanniae Radix Preparata suppresses bone loss and increases bone strength through interfering with canonical Wnt/β-catenin signaling pathway in OVX rats

Rehmanniae Radix Preparata (RRP) improves bone quality in OVX rats through the regulation of bone homeostasis via increasing osteoblastogenesis and decreasing osteoclastogenesis, suggesting it has a potential for the development of new anti-osteoporotic drugs.

INTRODUCTION

Determine the anti-osteoporotic effect of RRP in ovariectomized (OVX) rats and identify the signaling pathway involved in this process.

METHODS

OVX rats were treated with RRP aqueous extract for 14 weeks. The serum levels of tartrate-resistant acid phosphatase (TRAP), receptor activator of nuclear factor kappa-Β ligand (RANKL), alkaline phosphatase (ALP), and osteoprotegerin (OPG) were determined by ELISA. Bone histopathological alterations were evaluated by H&E, Alizarin red S, and Safranin O staining. Bone mineral density (BMD) and bone microstructure in rat femurs and lumbar bones were determined by dual-energy X-ray absorptiometry and micro-computed tomography. Femoral bone strength was detected by a three-point bending assay. The expression of Phospho-glycogen synthase kinase 3 beta (p-GSK-3β), GSK-3β, Dickkopf-related protein 1 (DKK1), cathepsin K, OPG, RANKL, IGF-1, Runx2, β-catenin, and p-β-catenin was determined by western blot and/or immunohistochemical staining.

RESULTS

Treatment of OVX rats with RRP aqueous extract rebuilt bone homeostasis demonstrated by increasing the levels of OPG as well as decreasing the levels of TRAP, RANKL, and ALP in serum. Furthermore, RRP treatment preserved BMD and mechanical strength by increasing cortical bone thickness and epiphyseal thickness as well as improving trabecular distribution in the femurs of OVX rats. In addition, RRP downregulated the expression of DKK1, sclerostin, RANKL, cathepsin K, and the ratio of p-β-catenin to β-catenin, along with upregulating the expression of IGF-1, β-catenin, and Runx2 and the ratio of p-GSK-3β to GSK-3β in the tibias and femurs of OVX rats. Echinacoside, jionoside A1/A2, acetoside, isoacetoside, jionoside B1, and jionoside B2 were identified in the RRP aqueous extract.

CONCLUSION

RRP attenuates bone loss and improves bone quality in OVX rats partly through its regulation of the canonical Wnt/β-catenin signaling pathway, suggesting that RRP has the potential to provide a new source of anti-osteoporotic drugs.

Pectolinarigenin prevents bone loss in ovariectomized mice and inhibits RANKL-induced osteoclastogenesis via blocking activation of MAPK and NFATc1 signaling

Osteoporosis (OP) is a metabolic disease caused by multiple factors, which is characterized by a reduction of bone mass per unit volume and destruction of bone microstructure. Aberrant osteoclast function is the main cause of OP, therefore, regulating the differentiation and function of osteoclast is one of the treatment strategies for OP. Pectolinarigenin (PEC) is a medicinal implant isolated from Fragrant Eupatorium. Our experimental data showed that PEC was able to inhibit receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis in vitro, by tartrate-resistant acid phosphatase (TRAcP) staining, Fibrous actin ring formation, and hydroxyapatite resorption assays. In terms of mechanism, PEC inhibited the expression of the osteoclastogenesis-related gene, including cathepsin K (Ctsk), matrix metalloproteinase 9 (Mmp9), and TRAcP (Acp5). Western blot analysis demonstrated that PEC could significantly block the activation of RANKL-induced mitogen-activated protein kinase signaling cascades and was able to suppress the protein expression of nuclear factor of activated T-cells and c-Fos. Meanwhile, the intracellular reactive oxygen species levels were also reduced by PEC in a concentration-dependent manner. Further, PEC could prevent the ovariectomy-induced bone loss in vivo. Summarizing all, our data suggested that PEC inhibits osteoclast formation and function and RANKL signaling pathways, and thus could potentially be used in the treatment the osteoclast-related bone loss diseases.

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.

Small molecule inhibitor RepSox prevented ovariectomy-induced osteoporosis by suppressing osteoclast differentiation and bone resorption

Osteoporosis (OP) is a serious metabolic disease that, due to the increased number or function of osteoclasts, results in increased bone brittleness and, therefore, fragile fracture. Some recent studies report the importance of the transforming growth factor β (TGFβ) pathway in bone homeostasis. RepSox is a small molecule inhibitor of TGFβRI that has a wide range of potential application in clinical medicine, except OP. The aim of our study is to evaluate the effects of RepSox on the differentiation and bone resorption of osteoclasts in vitro and in vivo in an ovariectomy (OVX)-induced OP model. An initial analysis showed TGFβRI messenger RNA expression in both bone samples and bone cells. In the in vitro study, RepSox inhibited the receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast differentiation and bone resorption activity. Real-time polymerase chain reaction (PCR) analysis showed that RepSox suppressed osteoclastic marker gene expression in both dose-dependent and time-dependent manners. In addition, RepSox did not affect osteoblast differentiation, migration or osteoblastic-specific gene expression in vitro. Furthermore, western blot analysis indicated the underlying mechanisms of the RepSox suppression of osteoclastogenesis via the Smad3 and c-Jun N-terminal kinase/activator protein-1 (JNK/AP-1) signaling pathways. Finally, our animal experiments revealed that RepSox prevented OVX-induced bone loss in vivo. Together, our data suggest that RepSox regulates osteoclast differentiation, bone resorption, and OVX-induced OP via the suppression of the Smad3 and JNK/AP-1 pathways.

MicroRNA-539 promotes osteoblast proliferation and differentiation and osteoclast apoptosis through the AXNA-dependent Wnt signaling pathway in osteoporotic rats

This study aims to explore the effects of miR-539 on osteoblast proliferation and differentiation and osteoclast apoptosis in a rat model of osteoporosis, and its mechanism involving the regulation of the AXIN1-mediated wingless-Int (Wnt) signaling pathway. A rat model of osteoporosis was successfully established by ovariectomy. With osteoblasts and osteoclasts of rats not receiving ovariectomy in the sham group as control, those of osteoporotic rats were treated with miR-539 inhibitor, miR-539 mimic, and AXIN1 shRNA. The expression of miR-53, AXIN1, the Wnt pathway related-genes, apoptosis related-genes, and osteogenic markers were measured by RT-qPCR and Western blot analysis, respectively. Alkaline phosphatase (ALP) activity in osteoblast and tartrate-resistant acid phosphatase (TRAP) activity in osteoclasts were determined after cell transfection. Osteoblast and osteoclast viability was assayed by CCK-8 assay. Cell cycle and apoptosis of osteoblasts and osteoclasts were detected by flow cytometry. Lastly, alizarin red S staining was used to detect mineralized nodules of osteoblasts. Firstly, we determined that miR-539 was down-regulated in osteoblast and osteoclast of osteoporotic rats and AXIN1 was negatively regulated by miR-539. Additionally, overexpression of miR-539 increased the expressions of β-catenin, LEF1, c-myc, cyclin D1, RUNX2, BGP, BMP-2 in osteoblast as well as β-catenin, RhoA, caspase-3, and Bcl-2 in osteoclasts. Finally, overexpression of miR-539 elevated ALP activity, proliferation, and mineralized nodules in osteoblast and osteoclast apoptosis, with reduced TRAP activity in osteoclasts. Our results demonstrate that miR-539 promotes osteoblast proliferation and differentiation as well as osteoclast apoptosis through the AXIN1-dependent Wnt signaling pathway in osteoporotic rats.

Lithium doped silica nanospheres/poly(dopamine) composite coating on polyetheretherketone to stimulate cell responses, improve bone formation and osseointegration

Osseointegration is crucial for early fixation as well as long-term success of orthopedic implants. Bioactive composite containing lithium doping silica nanospheres (LSNs) and poly(dopamine) (PDA) were coated on polyetheretherketone (PK) surface (LPPK), and effects of the LSNs/PDA composite (LPC) coating on the biological properties of LPPK were assessed both in vitro and in vivo. Results showed that LPPK with improved bioactivity remarkably promoted apatite mineralization in simulated body fluid (SBF) compared with PDA coated on PK (PPK) and PK. Moreover, the LPPK remarkably stimulated rat bone marrow stromal cells (rBMSCs) responses compared with PPK and PK. Furthermore, the LPPK significantly promoted bone tissues responses in vivo compared with PPK and PK. It could be suggested that the improvements of cells and bone tissues responses were attributed to the surface characteristics of the bioactive LPC coating on LPPK. The LPPK would be a great candidate for orthopedic and dental applications.

Topical zoledronic acid decreases micromotion induced bone resorption in a sheep arthroplasty model

Background

Initial micromotion of a total hip replacement is associated with aseptic loosening. The use of bisphosphonates could be one way to reduce peri-implant bone resorption induced by micromotion. Bisphosphonates compounds are inhibitors of bone resorption. The aim of this study was to investigate whether local treatment with bisphosphonate would reduce bone resorption and fibrous tissue around an experimental implant subjected to micromotion.

Methods

One micromotion implant were inserted into each medial femoral condyle in ten sheep. During each gait cycle the implant axially piston 0.5 mm. During surgery one of the femoral condyles were locally treated with 0.8 mg zoledronate. The other condyle served as control. Observation period was 12 weeks.

Results

Histological evaluation showed a fibrous capsule around both the control and bisphosphonate implants. Histomorphometrical analysis showed that 97% of the surface on both control and bisphosphonate implants were covered by fibrous tissue. However, the bisphosphonate was able to preserve bone in a 1 mm zone around the implants.

Conclusion

This study indicates that local treatment with bisphosphonate cannot prevent the formation of a fibrous capsule around an implant subjected to micromotion, but bisphosphonate is able to reduce resorption of peri-prosthetic bone.