Roles of Wnt signaling in bone formation and resorption

Osteogenic effect of an adiponectin-derived short peptide that rebalances bone remodeling: a potential disease-modifying approach for postmenopausal osteoporosis therapy

Adiponectin, an adipokine, regulates metabolic processes, including glucose flux, lipid breakdown, and insulin response, by activating adiponectin receptors 1 and 2 (AdipoR1 and AdipoR2). We have previously shown that globular adiponectin (gAd), an endogenous form of adiponectin, has osteoanabolic and anti-catabolic effects in rodent models of postmenopausal osteopenia. Moreover, we reported the identification of a 13-mer peptide (ADP-1) from the collagen domain of adiponectin, which exhibited significant adiponectin-mimetic properties. Since the clinical development of gAd is constrained by its large size, here, we investigated the osteogenic property of ADP-1. ADP-1 induced osteoblast differentiation more potently than gAd. ADP-1 elicited osteoblast differentiation through two downstream pathways that involved the participation of adiponectin receptors. Firstly, it enhanced mitochondrial biogenesis and OxPhos, leading to osteoblast differentiation. Secondly, it activated the Akt-glycogen synthase kinase 3β-Wnt pathway, thereby increasing osteoblast differentiation. Additionally, ADP-1 suppressed the production of receptor-activator of nuclear kappa B ligand from osteoblasts, enabling it to act as a dual-action molecule (suppressing osteoclast function besides promoting osteoblast function). In osteopenic ovariectomized rats, ADP-1 increased bone mass and strength and improved trabecular integrity by stimulating bone formation and inhibiting bone resorption. Furthermore, by increasing ATP-producing intermediates within the tricarboxylic acid cycle in bones, ADP-1 likely fueled osteoblast function. Given its dual-action mechanism and high potency, ADP-1 offers a unique opportunity to address the unmet clinical need to reset the aberrant bone remodeling in osteoporosis to normalcy, potentially offering a disease-modifying impact.

Osteoporosis induced by cellular senescence: A mathematical model

Osteoporosis is a disease characterized by loss of bone mass, where bones become fragile and more likely to fracture. Bone density begins to decrease at age 50, and a state of osteoporosis is defined by loss of more than 25%. Cellular senescence is a permanent arrest of normal cell cycle, while maintaining cell viability. The number of senescent cells increase with age. Since osteoporosis is an aging disease, it is natural to consider the question to what extend senescent cells induce bone density loss and osteoporosis. In this paper we use a mathematical model to address this question. We determine the percent of bone loss for men and women during age 50 to 100 years, and the results depend on the rate η of net formation of senescent cell, with η = 1 being the average rate. In the case η = 1, the model simulations are in agreement with empirical data. We also consider senolytic drugs, like fisetin and quercetin, that selectively eliminate senescent cells, and assess their efficacy in terms of reducing bone loss. For example, at η = 1, with estrogen hormonal therapy and early treatment with fisetin, bone density loss for women by age 75 is 23.4% (below osteoporosis), while with no treatment with fisetin it is 25.8% (osteoporosis); without even a treatment with estrogen hormonal therapy, bone loss of 25.3% occurs already at age 65.

A comprehensive review and advanced biomolecule-based therapies for osteoporosis

BACKGROUND

The prevalence of osteoporosis (OP) on a global scale is significantly elevated that causes life threatening issues. The potential of groundbreaking biomolecular therapeutics in the field of OP is highly encouraging. The administration of biomolecular agents has the potential to mitigate the process of bone demineralization while concurrently augmenting the regenerative capacity of bone tissue, thereby facilitating a personalized therapeutic approach. Biomolecules-based therapies showed promising results in term of bone mass protection and restoration in OP.

AIM OF REVIEW

We summarized the recent biomolecular therapies with notable progress in clinical, demonstrating the potential to transform illness management. These treatments frequently utilize different biomolecule based strategies. Biomolecular therapeutics has a targeted character, which results in heightened specificity and less off-target effects, ultimately leading to increased patient outcomes. These aspects have the capacity to greatly enhance the management of OP, thus resulting in a major enhancement in the quality of life encountered by individuals affected by this condition.

Aseptic loosening around total joint replacement in humans is regulated by miR-1246 and miR-6089 via the Wnt signalling pathway

BACKGROUND

Total joint replacement for osteoarthritis is one of the most successful surgical procedures in modern medicine. However, aseptic loosening continues to be a leading cause of revision arthroplasty. The diagnosis of aseptic loosening remains a challenge as patients are often asymptomatic until the late stages. MicroRNA (miRNA) has been demonstrated to be a useful diagnostic tool and has been successfully used in the diagnosis of other diseases. We aimed to identify differentially expressed miRNA in the plasma of patients with aseptic loosening.

METHODS

Adult patients undergoing revision arthroplasty for aseptic loosening and age- and gender-matched controls were recruited. Samples of bone, tissue and blood were collected, and RNA sequencing was performed in 24 patients with aseptic loosening and 26 controls. Differentially expressed miRNA in plasma was matched to differentially expressed mRNA in periprosthetic bone and tissue. Western blot was used to validate protein expression.

RESULTS

Seven miRNA was differentially expressed in the plasma of patients with osteolysis (logFC >|2|, adj-P < 0.05). Three thousand six hundred and eighty mRNA genes in bone and 427 mRNA genes in tissue samples of osteolysis patients were differentially expressed (logFC >|2|, adj-P < 0.05). Gene enrichment analysis and pathway analysis revealed two miRNA (miR-1246 and miR-6089) had multiple gene targets in the Wnt signalling pathway in the local bone and tissues which regulate bone metabolism.

CONCLUSION

These results suggest that aseptic loosening may be regulated by miR-1246 and miR-6089 via the Wnt signalling pathway.

Beyond boundaries: unraveling innovative approaches to combat bone-metastatic cancers

Evidence demonstrated that bones, liver, and lungs are the most common metastasis sites in some human malignancies, especially in prostate and breast cancers. Bone is the third most frequent target for spreading tumor cells among these organs and tissues. Patients with bone-metastatic cancers face a grim prognosis characterized by short median survival time. Current treatments have proven insufficient, as they can only inhibit metastasis or tumor progression within the bone tissues rather than providing a curative solution. Gaining a more profound comprehension of the interplay between tumor cells and the bone microenvironment (BME) is of utmost importance in tackling this issue. This knowledge will pave the way for developing innovative diagnostic and therapeutic approaches. This review summarizes the mechanisms underlying bone metastasis and discusses the clinical aspects of this pathologic condition. Additionally, it highlights emerging therapeutic interventions aimed at enhancing the quality of life for patients affected by bone-metastatic cancers. By synthesizing current research, this review seeks to shed light on the complexities of bone metastasis and offer insights for future advancements in patient care.

Bone repair and key signalling pathways for cell-based bone regenerative therapy: A review

Advances in cell-based regenerative therapy create new opportunities for the treatment of bone-related disorders and injuries, by improving the reparative phase of bone healing. Apart from the classical approach of bone grafting, the application of cell-based therapies, particularly stem cells (SCs), has gained a lot of attention in recent years. SCs play an important role in regenerative therapy due to their excellent ability to differentiate into bone-forming cells. Regeneration of new bone is regulated by a wide variety of signalling molecules and intracellular networks, which are responsible for coordinating cellular processes. The activated signalling cascade is significantly involved in cell survival, proliferation, apoptosis, and interaction with the microenvironment and other types of cells within the healing site. Despite the increasing evidence from studies conducted on signalling pathways associated with bone formation, the exact mechanism involved in controlling the differentiation stage of transplanted cells is not well understood. Identifying the key activated pathways involved in bone regeneration may allow for precise manipulation of the relevant signalling molecules within the progenitor cell population to accelerate the healing process. The in-depth knowledge of molecular mechanisms would be advantageous in improving the efficiency of personalised medicine and targeted therapy in regenerative medicine. In this review, we briefly introduce the theory of bone repair mechanism and bone tissue engineering followed by an overview of relevant signalling pathways that have been identified to play an important role in cell-based bone regenerative therapy.

Differentiation of osteoblasts: the links between essential transcription factors

Osteoblasts, cells derived from mesenchymal stem cells (MSCs) in the bone marrow, are cells responsible for bone formation and remodeling. The differentiation of osteoblasts from MSCs is triggered by the expression of specific genes, which are subsequently controlled by pro-osteogenic pathways. Mature osteoblasts then differentiate into osteocytes and are embedded in the bone matrix. Dysregulation of osteoblast function can cause inadequate bone formation, which leads to the development of bone disease. Various key molecules are involved in the regulation of osteoblastogenesis, which are transcription factors. Previous studies have heavily examined the role of factors that control gene expression during osteoblastogenesis, both in vitro and in vivo. However, the systematic relationship of these transcription factors remains unknown. The involvement of ncRNAs in this mechanism, particularly miRNAs, lncRNAs, and circRNAs, has been shown to influence transcriptional factor activity in the regulation of osteoblast differentiation. Here, we discuss nine essential transcription factors involved in osteoblast differentiation, including Runx2, Osx, Dlx5, β-catenin, ATF4, Ihh, Satb2, and Shn3. In addition, we summarize the role of ncRNAs and their relationship to these essential transcription factors in order to improve our understanding of the transcriptional regulation of osteoblast differentiation. Adequate exploration and understanding of the molecular mechanisms of osteoblastogenesis can be a critical strategy in the development of therapies for bone-related diseases.Communicated by Ramaswamy H. Sarma.

Assessing the relationship between single nucleotide polymorphisms in Wingless signaling pathway genes and sella turcica morphology

Sella turcica development involves molecular factors and genes responsible for ossification. It is possible that single nucleotide polymorphisms (SNPs) in key genes are involved in morphological variation of sella turcica. Genes belonging to the WNT signaling pathway are involved in the ossification process and are candidates of sella turcica morphology. This study aimed to evaluate if SNPs in WNT6 (rs6754599) and WNT10A (rs10177996 and rs3806557) genes are associated with the calcification and patterns of the sella turcica. Nonsyndromic individuals were included in the research. Cephalometric radiographs were examined and the sella calcification was evaluated and classified according to the calcification of the interclinoid ligament (no calcification, partial calcification, and incomplete calcification) and sella turcica pattern (normal sella turcica, bridge type A-ribbon-like fusion, bridge type B-extension of the clinoid processes, incomplete bridge, hypertrophic posterior clinoid process, hypotrophic posterior clinoid process, irregularity in the posterior part, pyramidal shape of the dorsum, double contour of the floor, oblique anterior wall, and oblique contour of the floor). DNA samples were used to evaluate SNPs in the WNT genes (rs6754599, rs10177996, and rs3806557) using real-time PCR. Chi-square test or Fisher's exact test were used to compare the allele and genotype distributions according to sella turcica phenotypes. The alpha was set as 5% for all comparisons. A total of 169 individuals were included, 133 (78.7%) present sella turcica partially or completely calcified. Sella turcica anomalies were found in 131 individuals (77.5%). Sella turcica bridge type A (27.8%), posterior hypertrophic clinoid process (17.1%), and sella turcica bridge type B (11.2%) were the most prevalent morphological patterns observed. Individuals carrying the TT genotype in rs10177996 (TT vs. CT + CC) had higher chance to present a partially calcified sella turcica (p = 0.047; Odds ratio = 2.27, Confidence Interval 95% 1.01-5.13). In conclusion, the SNP in WNT10A is associated with the calcification phenotype of the sella turcica, the pleiotropic effect of this gene should be taken into consideration in future studies.

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.

Differential bone remodeling mechanism in hindlimb unloaded and hibernating Daurian ground squirrels: a comparison between artificial and natural disuse within the same species

Loss of bone mass can occur in mammals after prolonged disuse but the situation for hibernators that are in a state of torpor for many months of the year is not yet fully understood. The present study assesses the bone remodeling mechanisms present in Daurian ground squirrels (Spermophilus dauricus) during hibernation as compared with a model of hindlimb disuse. Differences in microstructure, mechanical properties, bone remodeling-related proteins (Runx2, OCN, ALP, RANKL, CTK and MMP-9) and key proteins of Wnt/β-catenin signaling pathway (GSK-3β and phospho-β-catenin) were evaluated in ground squirrels under 3 conditions: summer active (SA) vs. hibernation (HIB) vs. hindlimb unloaded (HLU). The results indicated that the body weight in HLU ground squirrels was lower than the SA group, and the middle tibia diameter in the HLU group was lower than that in SA and HIB groups. The thickness of cortical and trabecular bone in femurs from HLU ground squirrels was lower than in SA and HIB groups. Most parameters of the tibia in the HLU group were lower than those in SA and HIB groups, which indicated cortical bone loss in ground squirrels. Moreover, our data showed that the changes in microscopic parameters in the femur were more obvious than those in the tibia in HLU and HIB ground squirrels. The levels of Runx2 and ALP were lower in HLU ground squirrels than SA and HIB groups. The protein levels of OCN were unchanged in the three groups, but the protein levels of ALP were lower in the HLU group than in SA and HIB groups. RANKL, CTK and MMP-9 protein levels were significantly decreased in tibia of HLU ground squirrels as compared with SA and HIB groups. In addition, the protein expression levels of RANKL, CTK and MMP-9 showed no statistical difference between SA and HIB ground squirrels. Thus, the mechanisms involved in the balance between bone formation and resorption in hibernating and hindlimb unloading ground squirrels may be different. The present study showed that in femur, the Wnt signaling pathway was inhibited, the protein level of GSK-3β was increased, and the protein expression of phospho-β-catenin was decreased in the HIB group as compared with the SA group, which indicates that the Wnt signaling pathway has a great influence on the femur of the HIB group. In conclusion, the natural anti-osteoporosis properties of Daurian ground squirrels are seasonal. The squirrels do not experience bone loss when they are inactive for a long time during hibernation, but the mechanisms of anti-osteoporosis did not work in HLU summer active squirrels.

USP53 Regulates Bone Homeostasis by Controlling Rankl Expression in Osteoblasts and Bone Marrow Adipocytes

In the skeleton, osteoblasts and osteoclasts synchronize their activities to maintain bone homeostasis and integrity. Investigating the molecular mechanisms governing bone remodeling is critical and helps understand the underlying biology of bone disorders. Initially, we have identified the ubiquitin-specific peptidase gene (Usp53) as a target of the parathyroid hormone in osteoblasts and a regulator of mesenchymal stem cell differentiation. Mutations in USP53 have been linked to a constellation of developmental pathologies. However, the role of Usp53 in bone has never been visited. Here we show that Usp53 null mice have a low bone mass phenotype in vivo. Usp53 null mice exhibit a pronounced decrease in trabecular bone indices including trabecular bone volume (36%) and trabecular number (26%) along with an increase in trabecular separation (13%). Cortical bone parameters are also impacted, showing a reduction in cortical bone volume (12%) and cortical bone thickness (15%). As a result, the strength and mechanical bone properties of Usp53 null mice have been compromised. At the cellular level, the ablation of Usp53 perturbs bone remodeling, augments osteoblast-dependent osteoclastogenesis, and increases osteoclast numbers. Bone marrow adipose tissue volume increased significantly with age in Usp53-deficient mice. Usp53 null mice displayed increased serum receptor activator of NF-κB ligand (RANKL) levels, and Usp53-deficient osteoblasts and bone marrow adipocytes have increased expression of Rankl. Mechanistically, USP53 regulates Rankl expression by enhancing the interaction between VDR and SMAD3. This is the first report describing the function of Usp53 during skeletal development. Our results put Usp53 in display as a novel regulator of osteoblast-osteoclast coupling and open the door for investigating the involvement of USP53 in pathologies. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Pharmacological inhibition of DKK1 promotes spine fusion in an ovariectomized rat model

Osteoporosis is common in patients undergoing spine surgery, and carries a considerable risk of adverse outcomes. New methods to positively influence bone regeneration and spine fusion under osteoporotic conditions would be impactful. Neutralizing anti-Dickkopf-1 (DKK1) antibodies has been used as a bone anabolic agent, and recently reported by our group to aid in stem cell-mediated appendicular bone regeneration. Here, a small molecule designed as a DKK1 inhibitor, WAY-262611, was used to induce posterolateral spine fusion in an ovariectomized rat model. In vitro, pharmacological inhibition of DKK1 enhanced osteogenesis and Wnt signaling activity among rat bone marrow-derived stem/stromal cells (BMSCs). In vivo, systemic treatment with WAY-262611 promoted both chondrogenesis and osteogenesis within the spinal fusion site, and ultimately led to significant improvements in lumbar fusion as assessed by XR, μCT, histology and manual palpation assessments. No significant effect on osteoclast numbers or fusion site angiogenesis was detected, suggesting a primary direct effect on mesenchymal cells of the implantation site. Finally, evidence from human stem/stromal cells further demonstrated that pharmacologic inhibition of DKK1 promoted osteogenic differentiation in vitro. Taken together, our results suggest that targeting DKK1 promotes local bone formation and suggests potential clinical value for osteoporotic bone repair.

Effects of Biological/Targeted Therapies on Bone Mineral Density in Inflammatory Arthritis

Inflammatory arthritis has been reported to be associated with the development of osteoporosis. Recent research has investigated the mechanisms of bone metabolism in chronic inflammatory arthritis such as rheumatoid arthritis (RA) and spondyloarthritis (SpA). Progress in both animal and clinical studies has provided a better understanding of the osteoclastogenesis-related pathways regarding the receptor activator of nuclear factor-κB ligand (RANKL), anti-citrullinated protein antibodies (ACPAs), and Wnt signaling and Dickkopf-related protein 1 (Dkk-1). The complex interplay between inflammatory cytokines and bone destruction has been elucidated, especially that in the interleukin-17/23 (IL-17/23) axis and Janus kinase and signal transducer and activator of transcription (JAK-STAT) signaling. Moreover, advances in biological and targeted therapies have achieved essential modifications to the bone metabolism of these inflammatory arthritis types. In this narrative review, we discuss recent findings on the pathogenic effects on bone in RA and SpA. Proinflammatory cytokines, autoantibodies, and multiple signaling pathways play an essential role in bone destruction in RA and SpA patients. We also reviewed the underlying pathomechanisms of bone structure in biological and targeted therapies of RA and SpA. The clinical implications of tumor necrosis factor inhibitors, abatacept, rituximab, tocilizumab, Janus kinase inhibitors, and inhibitors of the IL-17/23 axis are discussed. Since these novel therapeutics provide new options for disease improvement and symptom control in patients with RA and SpA, further rigorous evidence is warranted to provide a clinical reference for physicians and patients.

Nanomaterial-induced mesenchymal stem cell differentiation into osteoblast for counteracting bone resorption in the osteoporotic rats

The current approach was designed to unearth the therapeutic potential of osteoblasts infusion, yielded from cultivating rat mesenchymal stem cells of bone marrow source in osteogenic differentiation media supplied with either hydroxyapatite nanoparticles (HA-NPs), chitosan/hydroxyapatite nanomaterials (C/HA-NPs), or chitosan nanoparticles, in the osteoporotic rats. The successful migration of the osteoblasts to the diseased bones of rats in C/HA-NPs and HA-NPs groups was evidenced by PCR screening of the Y-linked sex-determining gene (SRY) in the femoral bone tissue. Serum bone biomarker levels and gene expression patterns of cathepsin K, receptor activator of nuclear factor kappa B ligand (RANKL), and osteoprotegerin (OPG) were assessed. Additionally, histological examination of the femoral bone tissues of rats was performed. The current outcomes revealed that osteoblast implantation, resulted from C/HA-NPs or HA-NPs group, significantly lessened bone sialoprotein level. In Addition, it yielded a significant decline in the gene expression patterns of cathepsin K, RANKL, and RANKL/OPG proportion as well as up-regulation in BMP-2 and Runx-2 gene expression levels as opposed to the untreated ovariectomized animals. Moreover, it could restrain bone resorption and refine bone histoarchitecture. Conclusively, this study sheds light on the therapeutic significance of osteoblasts transplantation in alleviating the intensity of the bone remodeling cycle, consequently representing a hopeful therapeutic approach for primary osteoporosis.

Hemp Seeds in Post-Arthroplasty Rehabilitation: A Pilot Clinical Study and an In Vitro Investigation

Osteoarthritis is a type of degenerative joint disease that results from the breakdown of joint cartilage and underlying bone. Due to their antioxidants and anti-inflammatory action, the phytochemical constituents of many vegetable varieties could represent a new frontier for the treatment of patients with Osteoarthritis and are still being explored. The aim of this pilot human study was to investigate the effects of pasta enriched with hemp seed flour on osteoarticular pain and bone formation markers in patients in post-arthroplasty rehabilitation. Another purpose was to evaluate the effect of hemp seed extract on bone metabolism, in vitro. A pilot, controlled, clinical study was conducted to verify the feasibility of pain symptom reduction in patients with Osteoarthritis undergoing arthroplasty surgery. We also investigated the effect of hemp seed extract on the Wnt/β-catenin and ERK1/2 pathways, alkaline phosphatase, RANKL, RUNX-2, osteocalcin, and COL1A on Saos-2. After 6 weeks, the consumption of hemp seed pasta led to greater pain relief compared to the regular pasta control group (−2.9 ± 1.3 cm vs. −1.3 ± 1.3 cm; p = 0.02). A significant reduction in serum BALP was observed in the participants consuming the hemp seed pasta compared to control group (−2.8 ± 3.2 µg/L vs. 1.1 ± 4.3 µg/L; p = 0.04). In the Saos-2 cell line, hemp seed extract also upregulated Wnt/β-catenin and Erk1/2 pathways (p = 0.02 and p = 0.03) and osteoblast differentiation markers (e.g., ALP, OC, RUNX2, and COL1A) and downregulated RANKL (p = 0.02), compared to the control. Our study demonstrated that hemp seed can improve pain symptoms in patients with osteoarthritis undergoing arthroplasty surgery and also improves bone metabolism both in humans and in vitro. However, more clinical studies are needed to confirm our preliminary findings.

Wnt Signaling in Vascular Calcification

Cardiovascular disease is a worldwide epidemic and considered the leading cause of death globally. Due to its high mortality rates, it is imperative to study the underlying causes and mechanisms of the disease. Vascular calcification, or the buildup of hydroxyapatite within the arterial wall, is one of the greatest contributors to cardiovascular disease. Medial vascular calcification is a predictor of cardiovascular events such as, but not limited to, hypertension, stiffness, and even heart failure. Vascular smooth muscle cells (VSMCs), which line the arterial wall and function to maintain blood pressure, are hypothesized to undergo a phenotypic switch into bone-forming cells during calcification, mimicking the manner by which mesenchymal stem cells differentiate into osteoblast cells throughout osteogenesis. RunX2, a transcription factor necessary for osteoblast differentiation and a target gene of the Wnt signaling pathway, has also shown to be upregulated when calcification is present, implicating that the Wnt cascade may be a key player in the transdifferentiation of VSMCs. It is important to note that the phenotypic switch of VSMCs from a healthy, contractile state to a proliferative, synthetic state is necessary in response to the vascular injury surrounding calcification. The lingering question, however, is if VSMCs acquire this synthetic phenotype through the Wnt pathway, how and why does this signaling occur? This review seeks to highlight the potential role of the canonical Wnt signaling pathway within vascular calcification based on several studies and further discuss the Wnt ligands that specifically aid in VSMC transdifferentiation.

Roles of MicroRNAs in Osteogenesis or Adipogenesis Differentiation of Bone Marrow Stromal Progenitor Cells

Bone marrow stromal cells (BMSCs) are multipotent cells which can differentiate into chondrocytes, osteoblasts, and fat cells. Under pathological stress, reduced bone formation in favour of fat formation in the bone marrow has been observed through a switch in the differentiation of BMSCs. The bone/fat switch causes bone growth defects and disordered bone metabolism in bone marrow, for which the mechanisms remain unclear, and treatments are lacking. Studies suggest that small non-coding RNAs (microRNAs) could participate in regulating BMSC differentiation by disrupting the post-transcription of target genes, leading to bone/fat formation changes. This review presents an emerging concept of microRNA regulation in the bone/fat formation switch in bone marrow, the evidence for which is assembled mainly from in vivo and in vitro human or animal models. Characterization of changes to microRNAs reveals novel networks that mediate signalling and factors in regulating bone/fat switch and homeostasis. Recent advances in our understanding of microRNAs in their control in BMSC differentiation have provided valuable insights into underlying mechanisms and may have significant potential in development of new therapeutics.

High-purity magnesium pin enhances bone consolidation in distraction osteogenesis via regulating Ptch protein activating Hedgehog-alternative Wnt signaling

Magnesium alloys are promising biomaterials for orthopedic implants because of their degradability, osteogenic effects, and biocompatibility. Magnesium has been proven to promote distraction osteogenesis. However, its mechanism of promoting distraction osteogenesis is not thoroughly studied. In this work, a high-purity magnesium pin developed and applied in rat femur distraction osteogenesis. Mechanical test, radiological and histological analysis suggested that high-purity magnesium pin can promote distraction osteogenesis and shorten the consolidation time. Further RNA sequencing investigation found that alternative Wnt signaling was activated. In further bioinformatics analysis, it was found that the Hedgehog pathway is the upstream signaling pathway of the alternative Wnt pathway. We found that Ptch protein is a potential target of magnesium and verified by molecular dynamics that magnesium ions can bind to Ptch protein. In conclusion, HP Mg implants have the potential to enhance bone consolidation in the DO application, and this process might be via regulating Ptch protein activating Hedgehog-alternative Wnt signaling.

Differential bone remodeling mechanism in hindlimb unloaded rats and hibernating Daurian ground squirrels: a comparison between artificial and natural disuse

To determine that differential bone remodeling mechanism (especially Wnt signaling) in hindlimb unloaded rats and hibernating Daurian ground squirrels, the bone microstructure, mechanical properties, and expression levels of bone remodeling related proteins and key proteins of Wnt/β-catenin signaling were analyzed in this study. The thickness of cortical and trabecular bone was decreased in femur of hindlimb unloaded rats, while it was maintained in femur of hibernating ground squirrels. Interestingly, the ultimate bending energy and ultimate normalized displacement were reduced and the bending rigidity was increased in tibia of hibernating ground squirrels. Besides, the protein level of Runx2 was decreased in femur and tibia of unloaded rats, while it was maintained in tibia and even increased in femur of hibernating ground squirrels. The protein levels of RANKL and MMP-9 were increased in femur and tibia in unloaded rats, while they were maintained in both femur and tibia of hibernating ground squirrels. The protein level of GSK-3β was increased in femur and tibia of unloaded rats, while it was maintained in both femur and tibia of hibernating ground squirrels. The phospho-β-catenin expression was increased in both femur and tibia of unloaded rats, while it was only decreased in femur, but maintained in tibia of hibernating ground squirrels. In conclusion, the femur and tibia in hindlimb unloaded rats showed obvious bone loss, while they mitigated disuse-induced bone loss in hibernating ground squirrels, involving differential protein expression of key molecules in bone remodeling. In comparison with hindlimb unloaded rats, promoting osteoblast differentiation through activating canonical GSK-3β/β-catenin signaling involving Runx2 might be an adaptation to natural disuse in femur of hibernating Daurian ground squirrels. However, there was no statistical change in the protein levels of bone formation related proteins, GSK-3β and phospho-β-catenin in tibia of hibernating Daurian ground squirrels.

Emerging insights into the comparative effectiveness of anabolic therapies for osteoporosis

Over the past three decades, the mainstay of treatment for osteoporosis has been antiresorptive agents (such as bisphosphonates), which have been effective with continued administration in lowering fracture risk. However, the clinical landscape has changed as adherence to these medications has declined due to perceived adverse effects. As a result, decreases in hip fracture rates that followed the introduction of bisphosphonates have now levelled off, which is coincident with a decline in the use of the antiresorptive agents. In the past two decades, two types of anabolic agents (including three new drugs), which represent a novel approach to improving bone quality by increasing bone formation, have been approved. These therapies are expected to lead to a new clinical paradigm in which anabolic agents will be used either alone or in combination with antiresorptive agents to build new bone and reduce fracture risk. This Review examines the mechanisms of action for these anabolic agents by detailing their receptor-activating properties for key cell types in the bone and marrow niches. Using these advances in bone biology as context, the comparative effectiveness of these anabolic agents is discussed in relation to other therapeutic options for osteoporosis to better guide their clinical application in the future.

The phytoestrogen glabrene prevents osteoporosis in ovariectomized rats through upregulation of the canonical Wnt/β-catenin signaling pathway

This study systematically investigated the effects of phytoestrogen glabrene on postmenopausal osteoporosis in an ovariectomy (OVX) rat model. Glabrene administration (25, 50, and 100 mg/kg) for 13 weeks can significantly slow down the body weight gain and slightly increase the uterus weight of OVX rats. The increased levels of U-Ca, U-P levels, urine DPD/creatinine, serum ALP, OCN, triglycerides, and total cholesterol induced by OVX were dramatically inhibited in rats, whereas no difference occurred for S-Ca and S-P in all groups. Furthermore, glabrene can enhance bone mineral density of the right femur, fourth-lumbar vertebra and tibia and improve biomechanical parameters, such as femoral neck loading force, three-point bending of the tibia, and vertebral compression in OVX rats. Moreover, glabrene greatly suppressed the expression of TRAP protein but increased OPG and BGP protein expression in tibia tissue of OVX rats. In addition, OVX-induced reduction of Lrp-5, β-catenin, Runx2, and Osx protein expression was all restored by glabrene treatment. The present study indicated that glabrene might be a potential alternative medicine for the prevention and treatment of postmenopausal osteoporosis via activation of the Wnt/β-catenin signaling pathway.

Blue Mussel-Derived Peptides PIISVYWK and FSVVPSPK Trigger Wnt/β-Catenin Signaling-Mediated Osteogenesis in Human Bone Marrow Mesenchymal Stem Cells

Marine-derived bioactive peptides have shown potential bone health promoting effects. Although various marine-derived bioactive peptides have potential nutraceutical or pharmaceutical properties, only a few of them are commercially available. This study presented an osteogenic mechanism of blue mussel-derived peptides PIISVYWK and FSVVPSPK as potential bone health promoting agents in human bone marrow-derived mesenchymal stem cells (hBMMSCs). Alkaline phosphatase (ALP) activity and mineralization were stimulated using PIISVYWK and FSVVPSPK as early and late markers of osteogenesis in a concentration-dependent manner. Western blot and RT-qPCR results revealed that PIISVYWK and FSVVPSPK increased osteoblast differentiation of hBMMSCs by activating canonical Wnt/β-catenin signaling-related proteins and mRNAs. Immunofluorescence images confirmed nuclear translocation of β-catenin in osteogenic differentiation. Treatment with the pharmacological inhibitor DKK-1 blocked PIISVYWK- and FSVVPSPK-induced ALP activity and mineralization, as well as mRNA expression of the canonical Wnt/β-catenin signaling pathway in hBMMSC differentiation into osteoblasts. These findings suggested that PIISVYWK and FSVVPSPK promoted the canonical Wnt/β-catenin signaling pathway in osteogenesis of hBMMSCs. Blue mussel-derived PIISVYWK and FSVVPSPK might help develop peptide-based therapeutic agents for bone-related diseases.

Compounds isolated from Euonymus spraguei Hayata induce ossification through multiple pathways

The process of bone metabolism includes catabolism of old or mature bone and anabolism of new bone, carried out by osteoclasts and osteoblasts respectively. Any imbalance in this process results in loss of bone mass or osteoporosis. Drugs available to combat osteoporosis have certain adverse effects and are unable to improve bone formation, hence identifying new agents to fulfil these therapeutic gaps is required. To expand the scope of potential agents that enhance bone formation, we identified Euonymus spraguei Hayata as a plant material that possesses robust osteogenic potential using human osteoblast cells. We isolated three compounds, syringaresinol (1), syringin (2), and (−)-epicatechin (3), from E. spraguei. Results demonstrated that syringin (2), and (−)-epicatechin (3), increased alkaline phosphatase activity significantly up to 131.01% and 130.67%, respectively; they also elevated mineral deposition with respective values of up to 139.39% and 138.33%. In addition, 2 and 3 modulated autophagy and the bone morphogenetic protein (BMP)-2 signaling pathway. Our findings demonstrated that 2 and 3 induced osteogenesis by targeting multiple pathways and therefore can be considered as potent multi-targeted drugs for bone formation against osteoporosis.

Wnt modulation in bone healing

Genetic studies have been instrumental in the field of orthopaedics for finding tools to improve the standard management of fractures and delayed unions. The Wnt signaling pathway that is crucial for development and maintenance of many organs also has a very promising pathway for enhancement of bone regeneration. The Wnt pathway has been shown to have a direct effect on stem cells during bone regeneration, making Wnt a potential target to stimulate bone repair after trauma. A more complete view of how Wnt influences animal bone regeneration has slowly come to light. This review article provides an overview of studies done investigating the modulation of the canonical Wnt pathway in animal bone regeneration models. This not only includes a summary of the recent work done elucidating the roles of Wnt and β-catenin in fracture healing, but also the results of thirty transgenic studies, and thirty-eight pharmacological studies. Finally, we discuss the discontinuation of sclerostin clinical trials, ongoing clinical trials with lithium, the results of Dkk antibody clinical trials, the shift into combination therapies and the future opportunities to enhance bone repair and regeneration through the modulation of the Wnt signaling pathway.

DNA methylation and gene expression of sFRP2, sFRP4, Dkk 1, and Wif1 during osteoblastic differentiation of bone marrow derived mesenchymal stem cells

OBJECTIVES

Bone marrow derived mesenchymal stem cells (BMSCs) are an irresistible choice for use in stem cell therapy and regenerative medicine. BMSCs osteoblastic differentiation is also important in bone development, diseases, malignancies, and cancers studies. Wnt signaling pathway antagonists, Dickkopf-1 (Dkk 1), Secreted Frizzled-Related Proteins (sFRPs), and Wnt Inhibitory Factor 1 (Wif1) play important roles in inducing osteoblastic differentiation. This study is the first to investigate the association between DNA methylation and gene expression of Dkk1, sFRP2, sFRP4, and Wif1 during BMSCs osteoblastic differentiation.

METHODS

Human BMSCs were isolated and characterized using flow cytometry. Then, cells were treated with osteo-differentiation medium for three weeks. Alizarin red S staining and polymerase chain reaction (PCR) (alkaline phosphatase/osteocalcin) were performed for confirmation. The expression of Dkk 1, sFRP2, sFRP4, and Wif1 genes was evaluated at days 7, 14, and 21 using real-time PCR. Methylation-specific PCR (MSP) was performed to detect the methylation status of the promoters of the genes.

RESULTS

Data showed significant decreases (P < 0.05) during various days of BMSCs differentiation, while the promoters of the genes remained mostly un-methylated.

CONCLUSIONS

The down-regulation of Dkk 1, sFRP2, sFRP4, and Wif1 regulates various stages of human BMSCs during osteoblastic differentiation. DNA methylation does not interfere in the down-regulation of these genes, except for Wif1. We propose that the Wnt antagonist gene promoters should remain un-methylated during osteoblastic differentiation of BMSCs and that the down-regulation of these genes may contribute to other epigenetic mechanisms, other than DNA methylation, which implicitly indicates the role of DNA methylation in osteogenic cancers.

Aberrantly activated Wnt/β-catenin pathway co-receptors LRP5 and LRP6 regulate osteoblast differentiation in the developing coronal sutures of an Apert syndrome (Fgfr2S252W /+ ) mouse model

BACKGROUND

Apert syndrome is an autosomal, dominant inherited disorder characterized by craniosynostosis and syndactyly caused by gain-of-function mutations in the fibroblast growth factor receptor 2 (FGFR2) gene. Wnt/β-catenin signaling plays critical roles in regulating the skeletal development. Here, we analyzed the role of this pathway in the developing coronal sutures (CS) of a murine Apert syndrome model (Fgfr2^S252W/+ ).

RESULTS

We observed aberrantly increased mRNA expression of Lrp5 and Lrp6 in CS of Fgfr2^S252W/+ mice, whereas both wild type (WT) and Fgfr2^S252W/+ mice showed similar expression of other Wnt/β-catenin-related genes, such as Wnt3, Wnt3a, Fzd4, Fzd6, Axin2, and Dkk1 as evidenced by in situ hybridization. Significantly increased Lrp5 and Lrp6 mRNA expression was observed by quantitative PCR analysis of cultured cells isolated from CS of Fgfr2^S252W/+ mice. Phospho-LRP5, phospho-LRP6, and non-phospho-β-catenin were upregulated in Fgfr2^S252W/+ CS compared with that in WT CS. Short-interfering RNA targeting Lrp5 and Lrp6 significantly reduced runt-related transcription factor 2, collagen type 1 alpha 1, and osteocalcin mRNA expression, and alkaline phosphatase activity in cultured cells.

CONCLUSIONS

The Wnt/β-catenin pathway was activated in the CS of Fgfr2^S252W/+ mice during craniofacial development, suggesting the involvement of the Wnt/β-catenin pathway in the pathogenesis of CS synostosis in Fgfr2^S252W/+ mice.

Mechanisms of the Osteogenic Switch of Smooth Muscle Cells in Vascular Calcification: WNT Signaling, BMPs, Mechanotransduction, and EndMT

Characterized by the hardening of arteries, vascular calcification is the deposition of hydroxyapatite crystals in the arterial tissue. Calcification is now understood to be a cell-regulated process involving the phenotypic transition of vascular smooth muscle cells into osteoblast-like cells. There are various pathways of initiation and mechanisms behind vascular calcification, but this literature review highlights the wingless-related integration site (WNT) pathway, along with bone morphogenic proteins (BMPs) and mechanical strain. The process mirrors that of bone formation and remodeling, as an increase in mechanical stress causes osteogenesis. Observing the similarities between the two may aid in the development of a deeper understanding of calcification. Both are thought to be regulated by the WNT signaling cascade and bone morphogenetic protein signaling and can also be activated in response to stress. In a pro-calcific environment, integrins and cadherins of vascular smooth muscle cells respond to a mechanical stimulus, activating cellular signaling pathways, ultimately resulting in gene regulation that promotes calcification of the vascular extracellular matrix (ECM). The endothelium is also thought to contribute to vascular calcification via endothelial to mesenchymal transition, creating greater cell plasticity. Each of these factors contributes to calcification, leading to increased cardiovascular mortality in patients, especially those suffering from other conditions, such as diabetes and kidney failure. Developing a better understanding of the mechanisms behind calcification may lead to the development of a potential treatment in the future.

Wnt signaling modulates macrophage polarization and is regulated by biomaterial surface properties

Macrophages are among the first cells to interact with biomaterials and ultimately determine their integrative fate. Biomaterial surface characteristics like roughness and hydrophilicity can activate macrophages to an anti-inflammatory phenotype. Wnt signaling, a key cell proliferation and differentiation pathway, has been associated with dysregulated macrophage activity in disease. However, the role Wnt signaling plays in macrophage activation and response to biomaterials is unknown. The aim of this study was to characterize the regulation of Wnt signaling in macrophages during classical pro- and anti-inflammatory polarization and in their response to smooth, rough, and rough-hydrophilic titanium (Ti) surfaces. Peri-implant Wnt signaling in macrophage-ablated (MaFIA) mice instrumented with intramedullary Ti rods was significantly attenuated compared to untreated controls. Wnt ligand mRNA were upregulated in a surface modification-dependent manner in macrophages isolated from the surface of Ti implanted in C57Bl/6 mice. In vitro, Wnt mRNAs were regulated in primary murine bone-marrow-derived macrophages cultured on Ti in a surface modification-dependent manner. When macrophageal Wnt secretion was inhibited, macrophage sensitivity to both physical and biological stimuli was abrogated. Loss of macrophage-derived Wnts also impaired recruitment of mesenchymal stem cells and T-cells to Ti implants in vivo. Finally, inhibition of integrin signaling decreased surface-dependent upregulation of Wnt genes. These results suggest that Wnt signaling regulates macrophage response to biomaterials and that macrophages are an important source of Wnt ligands during inflammation and healing.

Osteoblast-Based Therapy-A New Approach for Bone Repair in Osteoporosis: Pre-Clinical Setting

BACKGROUND

Osteoporosis is a metabolic bone disease characterized by low bone density resulting in increased fracture susceptibility. This research was constructed to uncover the potential therapeutic application of osteoblasts transplantation, generated upon culturing male rat bone marrow-derived mesenchymal stem cells (BM-MSCs) in osteogenic medium (OM), OM containing gold (Au-NPs) or gold/hydroxyapatite (Au/HA-NPs) nanoparticles, in ovariectomized rats to counteract osteoporosis.

METHODS

Forty rats were randomized into: (1) negative control, (2) osteoporotic rats, whereas groups (3), (4) and (5) constituted osteoporotic rats treated with osteoblasts yielded from culturing BM-MSCs in OM, OM plus Au-NPs or Au/HA-NPs, respectively. After 3 months, osterix (OSX), bone alkaline phosphatase (BALP), sclerostin (SOST) and bone sialoprotein (BSP) serum levels were assessed. In addition, gene expression levels of cathepsin K, receptor activator of nuclear factor-κb ligand (RANKL), osteoprotegerin (OPG) and RANKL/OPG ratio were evaluated using real-time PCR. Moreover, histological investigation of femur bone tissues in different groups was performed. The homing of implanted osteoblasts to the osteoporotic femur bone of rats was documented by Sex determining region Y gene detection in bone tissue.

RESULTS

Our results indicated that osteoblasts infusion significantly blunted serum BALP, BSP and SOST levels, while significantly elevated OSX level. Also, they brought about significant down-regulation in gene expression levels of cathepsin K, RANKL and RANKL/OPG ratio versus untreated osteoporotic rats. Additionally, osteoblasts nidation could restore bone histoarchitecture.

CONCLUSION

These findings offer scientific evidence that transplanting osteoblasts in osteoporotic rats regains the homeostasis of the bone remodeling cycle, thus providing a promising treatment strategy for primary osteoporosis.

The role of magnesium ions in bone regeneration involves the canonical Wnt signaling pathway

Magnesium (Mg)-based implants have become of interest to both academia and the medical industry. The attraction largely is due to Mg's biodegradability and ability to enhance bone healing and formation. However, the underlying mechanism of how Mg regulates osteogenesis is still unclear. Based on our previous in vivo and molecular signaling work demonstrating the osteogenic effect of Mg, the current study aims to extend this work at the molecular level especially that we also observed and quantified mineral deposits in the bone marrow space in a rabbit ulna fracture model with Mg plates and screws. Histological analysis and quantitative results of micro-CT showed mineralized deposition and a significant increase in bone volume at 8 weeks and 16 weeks post-operative. These in vivo results led us to focus on studying the effect of Mg²⁺ on human bone marrow stromal cells (hBMSCs). The data presented in this manuscript demonstrate the activation of the canonical Wnt signaling pathway in hBMSCs when treated with 10 mM Mg²⁺. With additional Mg²⁺ present, the protein expression of active β-catenin was significantly increased to a level similar to that of the positive control. Immunocytochemistry and the increased expression of LEF1 and Dkk1, downstream target genes that are controlled directly by active β-catenin, demonstrated the protein translocation and the activation of transcription. Taken together, these data suggest that Mg²⁺ induces an osteogenic effect in the bone marrow space by activating the canonical Wnt signaling pathway, which in turn causes BMSCs to differentiate toward the osteoblast lineage. STATEMENT OF SIGNIFICANCE: Magnesium (Mg)-based alloys are being studied to be used in the field of implantable medical devices due to its natural biodegradability and the potential ability to promote bone regeneration. Despite many in vivo studies that demonstrated an increased new bone growth by implanting Mg-based devices, the underlying mechanism of this effect is still unclear. In order to safely use Mg-based implants on human and better control the osteogenic effect, it is necessary to understand the corresponding cellular response in the targeted area. The present study provides the rationale to study Mg ions on bone marrow stromal cells and shows the activation of canonical Wnt signaling pathway that promotes osteogenesis by in vivo and in vitro approaches.

Mandible and iliac osteoblasts exhibit different Wnt signaling responses to LMHF vibration

Objective

The jaw bones and long bones have distinct developmental origins and respond differently to mechanical stimuli. This study aimed to compare the Wnt signaling responses of human mandible osteoblasts and long bone osteoblasts to low-magnitude, high-frequency (LMHF) mechanical vibration in vitro.

Methods

Primary human osteoblast cultures were prepared from mandibular bone (n = 3) and iliac bone (n = 3) specimens (six individuals). Osteoblast cell lines were subjected to vibration (0, 30, 60, 90, or 120 Hz) for 30 min. After 24 h, cells were vibrated for 30 min again, then harvested immediately to quantify Wnt10b, Wnt5a and runt-related transcription factor 2 (RUNX2) mRNA expression, β-catenin protein expression and alkaline phosphatase (ALP) activity.

Results

Mandible and iliac osteoblasts responded differently to LMHF vibration: Wnt10b mRNA was upregulated by the frequency range tested; Wnt5a, β-catenin protein expression and RUNX2 mRNA expression were not altered. Furthermore, vibration upregulated ALP activity in mandible osteoblasts, but not in iliac osteoblasts.

Conclusions

This study demonstrates mandible osteoblasts and long bone osteoblasts respond differently to LMHF mechanical vibration in terms of Wnt signaling expression and ALP activity. Therefore, the effects of whole-body vibration on the long bones cannot be generalized to the jaw bones. Furthermore, osteoblast-like cells mediate the cellular responses to vibration, at least in part, by secreting extracellular signaling molecules.

Interplay of Wnt β-catenin pathway and miRNAs in HBV pathogenesis leading to HCC

The prevalence of Hepatocellular carcinoma (HCC) has been identified world-wide. Plethora of factors including chronic infection of HBV/HCV has been characterized for the development of HCC. Although the onset and progression of HCC has been linked with awry of various signaling pathways but precise mechanism, still lies under the multitude layers of curiosity. HBV is spreading with insane speed throughout the world and has been found a main culprit in HCC development after regulating the several cellular pathways including Wnt/β-catenin, Raf/MAPK, Akt and affecting cell multiplication to genomic instability. The role of Wnt/FZD/β-catenin signaling pathway is centralized in liver functions and its anomalous activation leads to HCC development. β-catenin mainly plays a pivotal role in canonical pathway of the system. Altered mainly overexpression of β-catenin along its nuclear localization tunes the aberrations in liver functions and set disease progression. In the development of HCC, modulation of Wnt/FZD/β-catenin signaling pathway by HBV has been established. As HBV infects the cell it affects the miRNAs, the master regulators of cell. Previous studies showed the connection between HBV and cellular miRNAs. In the present review, we unveiled how HBV is deciphering the cellular miRNAs like miR-26a, miR-15a, miR-16-1, miR-148a, miR-132, miR-122, miR-34a, miR-21, miR-29a, miR-222 and miR-199a/b-3p to modulate the Wnt/FZD/β-catenin signaling pathway and develop HCC. These HBV mediated miRNAs may prove future therapeutic options to treat HBV-Wnt/FZD/β-catenin associated HCC.

Bone microenvironment signaling of cancer stem cells as a therapeutic target in metastatic prostate cancer

Prostate cancer (PCa) is one of the most prevalent cancers and the second leading cause of cancer death among US males. When diagnosed in an early disease stage, primary tumors of PCa may be treated with surgical resection or radiation, sometimes combined with androgen deprivation therapy, with favorable outcomes. Unfortunately, the treatment efficacy of each approach decreases significantly in later stages of PCa that involve metastasis to soft tissues and bone. Metastatic PCa is a heterogeneous disease containing host cells, mature cancer cells, and subpopulation of cancer stem cells (CSC). CSCs are highly tumorigenic due to their self-renewing and differentiating potential, clinically resulting in recurrence and resistance to standard therapies. Therefore, there is a large unmet clinical need to develop therapies, which target CSC activity. In this review, we summarize the main signaling pathways that are implicated in the current pre-clinical and clinical studies of recurrent metastatic PCa within the bone microenvironment targeting CSCs and discuss the trajectory of therapeutics moving forward.

Role of the Wnt/β-Catenin Pathway in Renal Osteodystrophy

Vascular calcification and bone fragility are common and interrelated health problems that affect chronic kidney disease (CKD) patients. Bone fragility, which leads to higher risk of fracture and mortality, arises from the abnormal bone remodeling and mineralization that are seen in chronic kidney disease. Recently, sclerostin and Dickkopf-related protein 1 were suggested to play a significant role in CKD-related bone disease as they are known inhibitors of the Wnt pathway, thus preventing bone formation. This review focuses on new knowledge about the Wnt pathway in bone, how its function is affected by chronic kidney disease and how this affects bone structure. Expression of components and inhibitors of the Wnt pathway has been shown to be affected by the loss of kidney function, and a better understanding of the bone effects of Wnt pathway inhibitors could allow the development of new therapies to prevent bone fragility in this population.

MODEL-BASED ANALYSIS OF IGF-1 EFFECT ON OSTEOBLAST AND OSTEOCLAST REGULATION IN BONE TURNOVER

The main determinant of bone Ca accretion is a bimolecular regulatory network on osteoblast (OB) and osteoclast (OC). Even though IGF-1 is known as an important regulator in bone cell cycle, little has been done to model IGF-1 action in bone cell regulation. Thus, the objective is to develop a mathematical model that depicts the regulatory action of IGF-1 onto the OB and OC interaction, and to evaluate adolescent and adult bone Ca accretion in response to differences in IGF-1 levels. As a result, a dynamic model of OB and OC with two main regulatory systems, i.e., Receptor Activator for Nuclear Factor [Formula: see text]B (RANK)-RANK Ligand (RANKL)-osteoprogerin (OPG) system, and TGF-[Formula: see text], was augmented with the IGF-1, and incorporated into Ca kinetic data to predict exchangeable bone Ca. The developed model could predict a change in OB and OC levels in response to perturbations in regulators, producing results consistent with bone physiology and published experimental data. The model also estimated parametric difference in regulators between adults and adolescents, suggesting that RANKL/OPG in adolescents was about 4 times higher than in adults, while adolescent serum PTH and IGF-1 concentrations were 60% and 220% of those of adults, respectively. This study highlighted the influence of IGF-1 on the regulation of bone cells in positively modulating bone Ca, suggesting that IGF-1 may be an effective target for reducing bone loss by promoting mature OB.

Anthraquinone Glycoside Aloin Induces Osteogenic Initiation of MC3T3-E1 Cells: Involvement of MAPK Mediated Wnt and Bmp Signaling

Osteoporosis is a bone pathology leading to increased fracture risk and challenging the quality of life. The aim of this study was to evaluate the effect of an anthraquinone glycoside, aloin, on osteogenic induction of MC3T3-E1 cells. Aloin increased alkaline phosphatase (ALP) activity, an early differentiation marker of osteoblasts. Aloin also increased the ALP activity in adult human adipose-derived stem cells (hADSC), indicating that the action of aloin was not cell-type specific. Alizarin red S staining revealed a significant amount of calcium deposition in cells treated with aloin. Aloin enhanced the expression of osteoblast differentiation genes, Bmp-2, Runx2 and collagen 1a, in a dose-dependent manner. Western blot analysis revealed that noggin and inhibitors of p38 MAPK and SAPK/JNK signals attenuated aloin-promoted expressions of Bmp-2 and Runx2 proteins. siRNA mediated blocking of Wnt-5a signaling pathway also annulled the influence of aloin, indicating Wnt-5a dependent activity. Inhibition of the different signal pathways abrogated the influence of aloin on ALP activity, confirming that aloin induced MC3T3-E1 cells into osteoblasts through MAPK mediated Wnt and Bmp signaling pathway.

Biological Events in Periodontal Ligament and Alveolar Bone Associated with Application of Orthodontic Forces

Orthodontic force-induced stresses cause dynamic alterations within the extracellular matrix and within the cytoskeleton of cells in the periodontal ligament and alveolar bone, mediating bone remodelling, ultimately enabling orthodontic tooth movement. In the periodontal ligament and alveolar bone, the mechanically induced tensile strains upregulate the expression of osteogenic genes resulting in bone formation, while mechanically induced compressive strains mediate predominantly catabolic tissue changes and bone resorption. In this review article we summarize some of the currently known biological events occurring in the periodontal ligament and in the alveolar bone in response to application of orthodontic forces and how these facilitate tooth movement.

Fluid flow modulates the expression of genes involved in the Wnt signaling pathway in osteoblasts in 3D culture conditions

The balance between osteoclastic bone resorption and osteoblastic bone formation maintains bone mass, while mechanical loads stimulate bone formation and suppress resorption. The molecular mechanisms responsible for this process have not yet been fully elucidated. In the present study, we assessed whether mechanical stimulation by pulsating fluid flow (PFF) leads to functional Wnt production and affects the function of osteoblasts. ROS17/2.8 osteoblasts were submitted to 1-4 h PFF (0.8 Pa) by three-dimensional (3D) cell culture system with fluid flow. PFF upregulated the gene expression levels of adenomatous polyposis coli, alkaline phosphatase, low density lipoprotein receptor-related protein 5 (LRP5), Wnt3a and β-catenin [catenin beta 1 (CTNNB1)] in all the groups of osteoblasts. Our results suggest that mechanical stimulation by PFF induces the differentiation of osteoblasts and the activation of the Wnt/β-catenin signaling pathway in a 3D cell culture system. Furthermore, mechanical stress plays an important role in the Wnt/β-catenin signaling pathway and is involved in bone formation.

The clinical utility of bone marker measurements in osteoporosis

Osteoporosis is characterised by low bone mass and structural deterioration of bone tissue, resulting in increased fragility and susceptibility to fracture. Osteoporotic fractures are a significant cause of morbidity and mortality. Direct medical costs from such fractures in the UK are currently estimated at over two billion pounds per year, resulting in a substantial healthcare burden that is expected to rise exponentially due to increasing life expectancy. Currently bone mineral density is the WHO standard for diagnosis of osteoporosis, but poor sensitivity means that potential fractures will be missed if it is used alone. During the past decade considerable progress has been made in the identification and characterisation of specific biomarkers to aid the management of metabolic bone disease. Technological developments have greatly enhanced assay performance producing reliable, rapid, non-invasive cost effective assays with improved sensitivity and specificity. We now have a greater understanding of the need to regulate pre-analytical sample collection to minimise the effects of biological variation. However, bone turnover markers (BTMs) still have limited clinical utility. It is not routinely recommended to use BTMs to select those at risk of fractures, but baseline measurements of resorption markers are useful before commencement of anti-resorptive treatment and can be checked 3–6 months later to monitor response and adherence to treatment. Similarly, formation markers can be used to monitor bone forming agents. BTMs may also be useful when monitoring patients during treatment holidays and aid in the decision as to when therapy should be recommenced. Recent recommendations by the Bone Marker Standards Working Group propose to standardise research and include a specific marker of bone resorption (CTX) and bone formation (P1NP) in all future studies. It is hoped that improved research in turn will lead to optimised markers for the clinical management of osteoporosis and other bone diseases.

A1330V polymorphism of the low-density lipoprotein receptor-related protein 5 gene and bone mineral density in Japanese male workers

OBJECTIVES

Both genetic and lifestyle factors have been shown to influence bone mineral density (BMD). We investigated the correlations between BMD and low-density lipoprotein receptor-related protein 5 (LRP5) A1330V (rs3736228) polymorphism, exercise, smoking, and alcohol intake in Japanese male workers.

METHODS

The subjects were 829 male employees (aged 20-59 years) of a large-scale integrated manufacturing facility in Japan. BMD was measured at the nondominant radius by dual-energy X-ray absorptiometry. Lifestyle information was obtained by a questionnaire at the same time, and genomic DNA was isolated from peripheral leukocytes.

RESULTS

Mean ± standard deviation (SD) BMD was 0.557 ± 0.059 g/cm(2). The genotype frequencies of LRP5 gene polymorphism were 51, 42, and 7% for AA, AV, and VV, respectively. Analysis of variance and post hoc Tukey test indicated that mean BMD was significantly lower in subjects with VV genotype than in those with AA genotype (0.540 ± 0.048 versus 0.562 ± 0.062 g/cm(2)). According to multiple linear regression analysis, LRP5 A1330V polymorphism was an independent determinant of BMD, after adjusting for age, body mass index (BMI), and lifestyle variables. Exercise (past or current) also influenced BMD.

CONCLUSIONS

These findings suggest that LRP5 A1330V polymorphism and exercise may influence BMD in Japanese male workers.