Targeting WNT signaling in the treatment of osteoporosis

Identification of potential sclerostin inhibiting flavonoids from Oroxylum indicum: an insilico approach

Flavonoids are secondary metabolites that are widely found in various medicinal plants. They are known for their medicinal benefits and have been extensively used in healthcare industries and in the management of age-related diseases. This paper focuses on flavonoids from Oroxylum indicum, a significant medicinal tree in the practice of traditional Indian medicine. O. indicum has been utilized in a variety of polyherbal formulations for the management of musculoskeletal disorders, however the mechanism of action of its bioactive flavonoids remains unknown. The present study aimed to identify the flavonoids of O. indicum with the potential to target sclerostin, an antagonist of canonical Wnt signaling pathway for the treatment of bone-related disorders. Molecular docking, coarse-grained and molecular dynamics simulations were performed to screen the major flavonoids and investigate their interaction with sclerostin. Flavonoids with highest binding affinity and interacting with at least one of the amino acids of the PNAIG motif residues were selected from docking studies and subjected to further drug likeness and ADMET screening. Further screening from coarse-grained and molecular dynamic simulations results showed that baicalein, compared to other screened flavonoids, stably binds with the important residues of the LRP6 binding site of sclerostin, resulting in pronounced structural changes in the protein. These findings suggest that baicalein from O. indicum can potentially inhibit sclerostin and can elicit skeletal protective effects, providing an insight for further in vitro and in vivo studies.Communicated by Ramaswamy H. Sarma.

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

Tumour necrosis factor α regulates the miR-27a-3p-Sfrp1 axis in a mouse model of osteoporosis

Osteoporosis is a metabolic bone disease that involves gradual loss of bone density and mass, thus resulting in increased fragility and risk of fracture. Inflammatory cytokines, such as tumour necrosis factor α (TNF-α), inhibit osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), and several microRNAs are implicated in osteoporosis development. This study aimed to explore the correlation between TNF-α treatment and miR-27a-3p expression in BMSC osteogenesis and further understand their roles in osteoporosis. An osteoporosis animal model was established using ovariectomized (OVX) mice. Compared with Sham mice, the OVX mice had a significantly elevated level of serum TNF-α and decreased level of bone miR-27a-3p, and in vitro TNF-α treatment inhibited miR-27a-3p expression in BMSCs. In addition, miR-27a-3p promoted osteogenic differentiation of mouse BMSCs in vitro, as evidenced by alkaline phosphatase staining and Alizarin Red-S staining, as well as enhanced expression of the osteogenic markers Runx2 and Osterix. Subsequent bioinformatics analysis combined with experimental validation identified secreted frizzled-related protein 1 (Sfrp1) as a downstream target of miR-27a-3p. Sfrp1 overexpression significantly inhibited the osteogenic differentiation of BMSCs in vitro and additional TNF-α treatment augmented this inhibition. Moreover, Sfrp1 overexpression abrogated the promotive effect of miR-27a-3p on the osteogenic differentiation of BMSCs. Furthermore, the miR-27a-3p-Sfrp1 axis was found to exert its regulatory function in BMSC osteogenic differentiation via regulating Wnt3a-β-catenin signalling. In summary, this study revealed that TNF-α regulated a novel miR-27a-3p-Sfrp1 axis in osteogenic differentiation of BMSCs. The data provide new insights into the development of novel therapeutic strategies for osteoporosis.

Amyloid-β neuropathology induces bone loss in male mice by suppressing bone formation and enhancing bone resorption

Alzheimer's disease (AD) and osteoporosis often coexist in the elderly. Although observational studies suggest an association between these two diseases, the pathophysiologic link between AD and skeletal health has been poorly defined. We examined the skeletal phenotype of 5xFAD mice, an AD model with accelerated neuron-specific amyloid-β accumulation causing full-blown AD phenotype by the age of 8 months. Micro-computed tomography indicated significantly lower trabecular and cortical bone parameters in 8-month-old male, but not female, 5xFAD mice than sex-matched wild-type littermates. Dynamic histomorphometry revealed reduced bone formation and increased bone resorption, and quantitative RT-PCR showed elevated skeletal RANKL gene expression in 5xFAD males. These mice also had diminished body fat percentage with unaltered lean mass, as determined by dual-energy X-ray absorptiometry (DXA), and elevated Ucp1 mRNA levels in brown adipose tissue, consistent with increased sympathetic tone, which may contribute to the osteopenia observed in 5xFAD males. Nevertheless, no significant changes could be detected between male 5xFAD and wild-type littermates regarding the serum and skeletal concentrations of norepinephrine. Thus, brain-specific amyloid-β pathology is associated with osteopenia and appears to affect both bone formation and bone resorption. Our findings shed new light on the pathophysiologic link between Alzheimer's disease and osteoporosis.

Natural Compounds for Bone Remodeling: A Computational and Experimental Approach Targeting Bone Metabolism-Related Proteins

Osteoporosis, characterized by reduced bone density and increased fracture risk, affects over 200 million people worldwide, predominantly older adults and postmenopausal women. The disruption of the balance between bone-forming osteoblasts and bone-resorbing osteoclasts underlies osteoporosis pathophysiology. Standard treatment includes lifestyle modifications, calcium and vitamin D supplementation and specific drugs that either inhibit osteoclasts or stimulate osteoblasts. However, these treatments have limitations, including side effects and compliance issues. Natural products have emerged as potential osteoporosis therapeutics, but their mechanisms of action remain poorly understood. In this study, we investigate the efficacy of natural compounds in modulating molecular targets relevant to osteoporosis, focusing on the Mitogen-Activated Protein Kinase (MAPK) pathway and the gut microbiome's influence on bone homeostasis. Using an in silico and in vitro methodology, we have identified quercetin as a promising candidate in modulating MAPK activity, offering a potential therapeutic perspective for osteoporosis treatment.

Bone-Targeted Supramolecular Nanoagonist Assembled by Accurate Ratiometric Herbal-Derived Therapeutics for Osteoporosis Reversal

Developing novel strategies for defeating osteoporosis has become a world-wide challenge with the aging of the population. In this work, novel supramolecular nanoagonists (NAs), constructed from alkaloids and phenolic acids, emerge as a carrier-free nanotherapy for efficacious osteoporosis treatment. These precision nanoagonists are formed through the self-assembly of berberine (BER) and chlorogenic acid (CGA), utilizing noncovalent electrostatic, π-π, and hydrophobic interactions. This assembly results in a 100% drug loading capacity and stable nanostructure. Furthermore, the resulting weights and proportions of CGA and BER within the NAs are meticulously controlled with strong consistency when the CGA/BER assembly feed ratio is altered from 1:1 to 1:4. As anticipated, our NAs themselves could passively target osteoporotic bone tissues following prolonged blood circulation, modulate Wnt signaling, regulate osteogenic differentiation, and ameliorate bone loss in ovariectomy-induced osteoporotic mice. We hope this work will open a new strategy to design efficient herbal-derived Wnt NAs for dealing with intractable osteoporosis.

Mechanical induction of osteoanabolic Wnt1 promotes osteoblast differentiation via Plat

Physical activity-induced mechanical stimuli play a crucial role in preserving bone mass and structure by promoting bone formation. While the Wnt pathway is pivotal for mediating the osteoblast response to loading, the exact mechanisms are not fully understood. Here, we found that mechanical stimulation induces osteoblastic Wnt1 expression, resulting in an upregulation of key osteogenic marker genes, including Runx2 and Sp7, while Wnt1 knockdown using siRNA prevented these effects. RNAseq analysis identified Plat as a major target through which Wnt1 exerts its osteogenic influence. This was corroborated by Plat depletion using siRNA, confirming its positive role in osteogenic differentiation. Moreover, we demonstrated that mechanical stimulation enhances Plat expression, which, in turn leads to increased expression of osteogenic markers like Runx2 and Sp7. Notably, Plat depletion by siRNA prevented this effect. We have established that Wnt1 regulates Plat expression by activating β-Catenin. Silencing Wnt1 impairs mechanically induced β-Catenin activation, subsequently reducing Plat expression. Furthermore, our findings showed that Wnt1 is essential for osteoblasts to respond to mechanical stimulation and induce Runx2 and Sp7 expression, in part through the Wnt1/β-Catenin/Plat signaling pathway. Additionally, we observed significantly reduced Wnt1 and Plat expression in bones from ovariectomy (OVX)-induced and age-related osteoporotic mouse models compared with non-OVX and young mice, respectively. Overall, our data suggested that Wnt1 and Plat play significant roles in mechanically induced osteogenesis. Their decreased expression in bones from OVX and aged mice highlights their potential involvement in post-menopausal and age-related osteoporosis, respectively.

Study on Synergistic Effects of Nanohydroxyapatite/High-Viscosity Carboxymethyl Cellulose Scaffolds Stimulated by LIPUS for Bone Defect Repair of Rats

Despite the self-healing capacity of bone, the regeneration of critical-size bone defects remains a major clinical challenge. In this study, nanohydroxyapatite (nHAP)/high-viscosity carboxymethyl cellulose (hvCMC, 6500 mPa·s) scaffolds and low-intensity pulsed ultrasound (HA-LIPUS) were employed to repair bone defects. First, hvCMC was prepared from ramie fiber, and the degree of substitution (DS), purity, and content of NaCl of hvCMC samples were 0.91, 99.93, and 0.017%, respectively. Besides, toxic metal contents were below the permissible limits for pharmaceutically used materials. Our results demonstrated that the hvCMC is suitable for pharmaceutical use. Second, nHAP and hvCMC were employed to prepare scaffolds by freeze-drying. The results indicated that the scaffolds were porous, and the porosity was 35.63 ± 3.52%. Subsequently, the rats were divided into four groups (n = 8) randomly: normal control (NC), bone defect (BD), bone defect treated with nHAP/hvCMC scaffolds (HA), and bone defect treated with nHAP/hvCMC scaffolds and stimulated by LIPUS (HA-LIPUS). After drilling surgery, nHAP/hvCMC scaffolds were implanted in the defect region of HA and HA-LIPUS rats. Meanwhile, HA-LIPUS rats were treated by LIPUS (1.5 MHz, 80 mW cm-2) irradiation for 2 weeks. Compared with BD rats, the maximum load and bone mineral density of HA-LIPUS rats were increased by 20.85 and 51.97%, respectively. The gene and protein results indicated that nHAP/hvCMC scaffolds and LIPUS promoted the bone defect repair and regeneration of rats significantly by activating Wnt/β-catenin and inhibiting OPG/RANKL signaling pathways. Overall, compared with BD rats, nHAP/hvCMC scaffolds and LIPUS promoted bone defect repair significantly. Furthermore, the research results also indicated that there are synergistic effects for bone defect repair between the nHAP/hvCMC scaffolds and LIPUS.

Investigating the impact of Wnt pathway-related genes on biomarker and diagnostic model development for osteoporosis in postmenopausal females

The Wnt signaling pathway is essential for bone development and maintaining skeletal homeostasis, making it particularly relevant in osteoporosis patients. Our study aimed to identify distinct molecular clusters associated with the Wnt pathway and develop a diagnostic model for osteoporosis in postmenopausal Caucasian women. We downloaded three datasets (GSE56814, GSE56815 and GSE2208) related to osteoporosis from the GEO database. Our analysis identified a total of 371 differentially expressed genes (DEGs) between low and high bone mineral density (BMD) groups, with 12 genes associated with the Wnt signaling pathway, referred to as osteoporosis-associated Wnt pathway-related genes. Employing four independent machine learning models, we established a diagnostic model using the 12 osteoporosis-associated Wnt pathway-related genes in the training set. The XGB model showed the most promising discriminative potential. We further validate the predictive capability of our diagnostic model by applying it to three external datasets specifically related to osteoporosis. Subsequently, we constructed a diagnostic nomogram based on the five crucial genes identified from the XGB model. In addition, through the utilization of DGIdb, we identified a total of 30 molecular compounds or medications that exhibit potential as promising therapeutic targets for osteoporosis. In summary, our comprehensive analysis provides valuable insights into the relationship between the osteoporosis and Wnt signaling pathway.

Exploring the Role of Wnt Ligands in Osteogenic Differentiation of Human Periodontal Ligament Stem Cells

OBJECTIVES

This study aimed to investigate the functions of 19 types of Wnt ligands during the process of osteogenic differentiation in human periodontal ligament stem cells (hPDLSCs), with particular attention to WNT3A and WNT4.

MATERIALS AND METHODS

The expression levels of 19 types of Wnt ligands were examined using real-time quantitative polymerase chain reaction (real-time qPCR) during hPDLSCs osteogenic differentiation at 7, 10, and 14 days. Knockdown of WNT3A and WNT4 expression was achieved using adenovirus vectors, and conditioned medium derived from WNT3A and WNT4 overexpression plasmids was employed to investigate their roles in hPDLSCs osteogenesis. Osteogenic-specific genes were analyzed using real-time qPCR. Alkaline phosphatase (ALP) and alizarin red S activities and staining were employed to assess hPDLSCs' osteogenic differentiation ability.

RESULTS

During hPDLSCs osteogenic differentiation, the expression of 19 types of Wnt ligands varied, with WNT3A and WNT4 showing significant upregulation. Inhibiting WNT3A and WNT4 expression hindered hPDLSCs' osteogenic capacity. Conditioned medium of WNT3A promoted early osteogenic differentiation, while WNT4 facilitated late osteogenesis slightly.

CONCLUSION

Wnt ligands, particularly WNT3A and WNT4, play an important role in hPDLSCs' osteogenic differentiation, highlighting their potential as promoters of osteogenesis.

CLINICAL RELEVANCE

Given the challenging nature of alveolar bone regeneration, therapeutic strategies that target WNT3A and WNT4 signaling pathways offer promising opportunities. Additionally, innovative gene therapy approaches aimed at regulating of WNT3A and WNT4 expression hold potential for improving alveolar bone regeneration outcomes.

Association between AXIN1 gene polymorphism (rs9921222) of WNT signaling pathway and susceptibility to osteoporosis in Egyptian patients: a case-control study

BACKGROUND

Osteoporosis (OP) is the most prevalent metabolic bone disease. Numerous genetic loci are strongly related to OP. AXIN1 is a significant gene that serves an important role in the WNT signaling pathway. The aim of this study was to explore the association between the AXIN1 genetic polymorphism (rs9921222) and OP susceptibility.

METHODS

A total of 101 subjects were enrolled in the study (50 patients with OP and 51 healthy individuals). Genomic DNA was extracted from whole blood using the QIAamp DNA Blood Mini Kit, and the AXIN1 gene polymorphism (rs9921222) was genotyped by TaqMan allelic discrimination assays. A logistic regression analysis was used to assess the association between genotypes and OP risk.

RESULTS

We found that AXIN1 rs9921222 had a significant association with the susceptibility of OP under the homozygote model (TT vs. CC: OR = 16.6, CI = 2.03-136.4, p = 0.009), (CT vs. CC: OR = 6.3, CI = 1.23-31.8, p = 0.027), recessive genetic model (TT vs.TC-CC: OR = 13.6, CI = 1.7-110.4, p = 0.015), and the dominant model (TT-TC vs. CC: OR = 9.7, CI = 2.6-36.3, p < 0.001). Allele T was significantly associated with OP risk (T vs. C: OR = 10.5, CI = 3.5-31.15, p = 0.001). There was a statistically significant difference between genotypes in mean platelet volume (p = 0.004), and platelet distribution width (p = 0.025). In addition, lumbar spine bone density, and femur neck bone density were significantly different between genotypes (p < 0.001).

CONCLUSION

AXIN1 rs9921222 was associated with OP susceptibility in the Egyptian population and should be considered a potential determinant risk for OP.

Antibodies to sclerostin or G-CSF receptor partially eliminate bone or marrow adipocyte loss, respectively, following vertical sleeve gastrectomy

Vertical sleeve gastrectomy (VSG), the most utilized bariatric procedure in clinical practice, greatly reduces body weight and improves a variety of metabolic disorders. However, one of its long-term complications is bone loss and increased risk of fracture. Elevated circulating sclerostin (SOST) and granulocyte-colony stimulating factor (G-CSF) concentrations have been considered as potential contributors to VSG-associated bone loss. To test these possibilities, we administrated antibodies to SOST or G-CSF receptor and investigated alterations to bone and marrow niche following VSG. Neutralizing either SOST or G-CSF receptor did not alter beneficial effects of VSG on adiposity and hepatic steatosis, and anti-SOST treatment provided a further improvement to glucose tolerance. SOST antibodies partially reduced trabecular and cortical bone loss following VSG by increasing bone formation, whereas G-CSF receptor antibodies had no effects on bone mass. The expansion in myeloid cellularity and reductions in bone marrow adiposity seen with VSG were partially eliminated by treatment with Anti-G-CSF receptor. Taken together, these experiments demonstrate that antibodies to SOST or G-CSF receptor may act through independent mechanisms to partially block effects of VSG on bone loss or marrow niche cells, respectively.

Effects of E'Jiao on Skeletal Mineralisation, Osteocyte and WNT Signalling Inhibitors in Ovariectomised Rats

E'Jiao is a traditional Chinese medicine derived from donkey skin. E'Jiao is reported to suppress elevated bone remodelling in ovariectomised rats but its mechanism of action is not known. To bridge this research gap, the current study aims to investigate the effects of E'Jiao on skeletal mineralisation, osteocyte and WNT signalling inhibitors in ovariectomised rats. Female Sprague-Dawley rats (3 months old) were ovariectomised and supplemented with E'Jiao at 0.26 g/kg, 0.53 g/kg and 1.06 g/kg, or 1% calcium carbonate (w/v) in drinking water. The rats were euthanised after two months of supplementation and their bones were collected for Fourier-transform infrared spectroscopy, histomorphometry and protein analysis. Neither ovariectomy nor treatment affected the skeletal mineral/matrix ratio, osteocyte number, empty lacunar number, and Dickkopf-1 and sclerostin protein levels (p > 0.05). Rats treated with calcium carbonate had a higher Dickkopf-1 level than baseline (p = 0.002) and E'Jiao at 0.53 g/kg (p = 0.002). In conclusion, E'Jiao has no significant effect on skeletal mineralisation, osteocyte and WNT signalling inhibitors in ovariectomised rats. The skeletal effect of E'Jiao might not be mediated through osteocytes.

The Role of Consumption of Molybdenum Biofortified Crops in Bone Homeostasis and Healthy Aging

Osteoporosis is a chronic disease and public health issue in aging populations. Inadequate intake of micronutrients increases the risk of bone loss during an adult's lifespan and therefore of osteoporosis. The aim of the study was to analyze the effects of consumption of biofortified crops with the micronutrient molybdenum (Mo) on bone remodeling and metabolism in a population of adults and seniors. The trial enrolled 42 senior and 42 adult people randomly divided into three groups that consumed lettuce biofortified with molybdenum (Mo-biofortified group) or without biofortification (control group) or molybdenum in a tablet (Mo-tablet group) for 12 days. We chose an experimental period of 12 days because the bone remodeling marker levels are influenced in the short term. Therefore, a period of 12 days allows us to determine if there are changes in the indicators. Blood samples, obtained at time zero and at the end of the study, were compared within the groups adults and seniors for the markers of bone resorption, C-terminal telopeptide (CTX) and bone formation osteocalcin, along with the markers of bone metabolism, parathyroid hormone (PTH), calcitonin, albumin-adjusted calcium, vitamin D, phosphate and potassium. Consumption of a Mo tablet did not affect bone metabolism in the study. Consumption of Mo-biofortified lettuce significantly reduced levels of CTX and PTH and increased vitamin D in adults and seniors while levels of osteocalcin, calcitonin, calcium, potassium and phosphate were not affected. The study opens up new considerations about the role of nutrition and supplementation in the prevention of chronic diseases in middle-aged and older adults. Consumption of Mo-biofortified lettuce positively impacts bone metabolism in middle-aged and older adults through reduced bone resorption and improved bone metabolism while supplementation of Mo tablets did not affect bone remodeling or metabolism. Therefore, Mo-biofortified lettuce may be used as a nutrition intervention to improve bone homeostasis and prevent the occurrence of osteoporosis in the elderly.

Long Noncoding RNA NORAD Promotes Fracture Healing through Interacting with Osteoblast Differentiation via Targeting miR-26a

The present study was designed to evaluate the dynamic expression of lncRNA NORAD in fracture healing of patients with brittle fractures and explore the function and mechanism of NORAD in regulating osteoblastic proliferation, differentiation, and apoptosis. The expression level of NORAD was detected by quantitative real-time PCR. The proliferation, differentiation, and apoptosis of osteoblasts were analyzed by MTT assay, ELISA, and flow cytometry. Luciferase report analysis was used to confirm the interaction between NORAD and its target ceRNA miR-26a. This study showed no significant differences in serum NORAD expression on the 7th day during fracture healing in patients, but increased expression of NORAD was certified on the 14, 21, and 28 days after fixation. Overexpression of NORAD promoted the proliferation and differentiation of osteoblasts and suppressed the apoptosis of osteoblasts. miR-26a proved to be the target gene of NORAD and was inhibited by overexpression of NORAD in osteoblasts. The enhanced expression of miR-26a was negatively linked to the lessened expression of NORAD. NORAD could accelerate the proliferation and differentiation of osteoblasts and inhibit apoptosis, thereby promoting fracture healing.

Romosozumab for the treatment of postmenopausal women at high risk of fracture

INTRODUCTION

Romosozumab is a monoclonal antibody that binds to sclerostin (an inhibitor of the Wingless-related integration site (Wnt) signaling pathway). It is a new osteoanabolic drug that simultaneously increases bone formation and decreases bone resorption. It has recently been approved by the US and EU authorities in postmenopausal women with at high risk of fractures.

AREAS COVERED

The literature on romosozumab in preclinical and in phase II and III clinical studies has been reviewed about the effect on bone, bone markers, and fracture reduction and its safety.

EXPERT OPINION

Compared to antiresorptive agents, its unique mechanism of action results in a quicker and greater increase in bone mineral density, it repairs and restores trabecular and cortical bone microarchitecture, and reduces fracture risk more rapidly and more effectively than alendronate, with persisting effects for at least two years after transition to antiresorptive agents. This finding has introduced the concept that, in patients at very high risk of fractures, the optimal sequence of treatment is to start with an osteoanabolic agent, followed by a potent AR drug. Recent national and international guidelines recommend the use of romosozumab as an initial treatment in patients at very high fracture risk without a history of stroke or myocardial infarction.

ED-71 Prevents Glucocorticoid-Induced Osteoporosis by Regulating Osteoblast Differentiation via Notch and Wnt/β-Catenin Pathways

PURPOSE

Long-term glucocorticoid- usage can lead to glucocorticoid-induced osteoporosis (GIOP). The study focused on the preventative effects of a novel active vitamin D3 analog, eldecalcitol (ED-71), against GIOP and explored the underlying molecular mechanisms.

METHODS

Intraperitoneal injection of methylprednisolone (MPED) or dexamethasone (DEX) induced the GIOP model within C57BL/6 mice in vivo. Simultaneously, ED-71 was orally supplemented. Bone histological alterations, microstructure parameters, novel bone formation rates, and osteogenic factor changes were evaluated by hematoxylin-eosin (HE) staining, micro-computed tomography, calcein/tetracycline labeling, and immunohistochemical (IHC) staining. The osteogenic differentiation level and mineralization in pre-osteoblast MC3T3-E1 cells were evaluated in vitro using alkaline phosphatase (ALP) staining, alizarin red (AR) staining, quantitative polymerase chain reaction (qPCR), Western blotting, and immunofluorescence staining.

RESULTS

ED-71 partially prevented bone mass reduction and microstructure parameter alterations among GIOP-induced mice. Moreover, ED-71 also promoted new bone formation and osteoblast activity while inhibiting osteoclasts. In vitro, ED-71 promoted osteogenic differentiation and mineralization in DEX-treated MC3T3-E1 cells and boosted the levels of osteogenic-related factors. Additionally, GSK3-β and β-catenin expression levels were elevated after ED-71 was added to cells and were accompanied by reduced Notch expression. The Wnt signaling inhibitor XAV939 and Notch overexpression reversed the ED-71 promotional effects toward osteogenic differentiation and mineralization.

CONCLUSION

ED-71 prevented GIOP by enhancing osteogenic differentiation through Notch and Wnt/GSK-3β/β-catenin signaling. The results provide a novel translational direction for the clinical application of ED-71 against GIOP.

Molecular mechanisms, physiological roles, and therapeutic implications of ion fluxes in bone cells: Emphasis on the cation-Cl- cotransporters

Bone turnover diseases are exceptionally prevalent in human and come with a high burden on physical health. While these diseases are associated with a variety of risk factors and causes, they are all characterized by common denominators, that is, abnormalities in the function or number of osteoblasts, osteoclasts, and/or osteocytes. As such, much effort has been deployed in the recent years to understand the signaling mechanisms of bone cell proliferation and differentiation with the objectives of exploiting the intermediates involved as therapeutic preys. Ion transport systems at the external and in the intracellular membranes of osteoblasts and osteoclasts also play an important role in bone turnover by coordinating the movement of Ca²⁺ , PO₄ ^2- , and H⁺ ions in and out of the osseous matrix. Even if they sustain the terminal steps of osteoformation and osteoresorption, they have been the object of very little attention in the last several years. Members of the cation-Cl^- cotransporter (CCC) family are among the systems at work as they are expressed in bone cells, are known to affect the activity of Ca²⁺ -, PO₄ ^2- -, and H⁺ -dependent transport systems and have been linked to bone mass density variation in human. In this review, the roles played by the CCCs in bone remodeling will be discussed in light of recent developments and their potential relevance in the treatment of skeletal disorders.

The effects of romosozumab combined with active vitamin D3 on fracture healing in ovariectomized rats

Background

In this study, we investigated the potential acceleration of fracture healing and bone mineral density-increasing effects of romosozumab and active vitamin D₃ combination therapy for fractures in ovariectomized rats.

Methods

Ovariectomy was performed on 40 24-week-old female Sprague–Dawley rats. After 8 weeks, the rats were subjected to periosteum removal and osteotomy of the femoral shaft followed by osteosynthesis with intramedullary nailing to create fracture models. The rats were then divided into four groups: C group (control), R group (receiving romosozumab at 25 mg/kg once a month via subcutaneous injection), VD group (receiving active vitamin D₃ at 0.2 µg/kg twice a week via subcutaneous injection), and R + VD group. Further, 10 rats were included in a sham group. At 10 weeks after the intervention, both femurs were removed and blood samples were collected from all rats. Soft X-ray imaging was used to evaluate bone union, and microcomputed tomography (micro-CT) was used for bone morphometric evaluation. Toluidine blue staining was used for the histopathological evaluation of the undecalcified specimens, and bone turnover marker levels were measured using enzyme-linked immunosorbent assay.

Results

Bone morphometry analysis via micro-CT revealed increased mineral density of the trabecular bone in the R + VD group femurs, demonstrating the effectiveness of romosozumab plus active vitamin D₃ combination therapy. However, there were no differences in bone union evaluated using soft X-ray imaging, indicating no acceleration of fracture healing.

Conclusions

Although romosozumab and active vitamin D₃ combination therapy increased trabecular bone volume, there was no evidence on its ability to accelerate fracture healing.

Graphical abstract

Salt inducible kinases and PTH1R action

Parathyroid hormone is a central regulator of calcium homeostasis. PTH protects the organism from hypocalcemia through its actions in bone and kidney. Recent physiologic studies have revealed key target genes for PTH receptor (PTH1R) signaling in these target organs. However, the complete signal transduction cascade used by PTH1R to accomplish these physiologic actions has remained poorly defined. Here we will review recent studies that have defined an important role for salt inducible kinases downstream of PTH1R in bone, cartilage, and kidney. PTH1R signaling inhibits the activity of salt inducible kinases. Therefore, direct SIK inhibitors represent a promising novel strategy to mimic PTH actions using small molecules. Moreover, a detailed understanding of the molecular circuitry used by PTH1R to exert its biologic effects will afford powerful new models to better understand the diverse actions of this important G protein coupled receptor in health and disease.

Structural Analysis and Development of Notum Fragment Screening Hits

The Wnt signaling suppressor Notum is a promising target for osteoporosis, Alzheimer's disease, and colorectal cancers. To develop novel Notum inhibitors, we used an X-ray crystallographic fragment screen with the Diamond-SGC Poised Library (DSPL) and identified 59 fragment hits from the analysis of 768 data sets. Fifty-eight of the hits were found bound at the enzyme catalytic pocket with potencies ranging from 0.5 to >1000 μM. Analysis of the fragments' diverse binding modes, enzymatic inhibitory activities, and chemical properties led to the selection of six hits for optimization, and five of these resulted in improved Notum inhibitory potencies. One hit, 1-phenyl-1,2,3-triazole 7, and its related cluster members, have shown promising lead-like properties. These became the focus of our fragment development activities, resulting in compound 7d with IC50 0.0067 μM. The large number of Notum fragment structures and their initial optimization provided an important basis for further Notum inhibitor development.

Potential of RNA-binding protein human antigen R as a driver of osteogenic differentiation in osteoporosis

Background

Emerging evidence has correlated the human antigen R (HuR) with the low-density lipoprotein receptor-related protein 6 (LRP6) gene, an important therapeutic target for osteoporosis. Herein, we sought to probe the regulatory role of HuR in the LRP6 gene and their interaction in the progression of osteoporosis.

Methods

HuR and downstream potential target genes were predicted by bioinformatics analysis to identify their potential functions in bone metabolism following osteoporosis. The effect of HuR on the osteoblastic differentiation and viability and apoptosis of mouse embryo osteoblast precursor cells (MC3T3-E1) was evaluated after artificial modulation of HuR expression.

Results

Bone phenotypes were observed in ovariectomized mice in response to adenovirus-mediated HuR overexpression. Poor expression of HuR was identified in the bone tissues of ovariectomized mice. Silencing of HuR inhibited the osteoblastic differentiation of MC3T3-E1 cells, as evidenced by decreased expression of Runx2 and Osterix along with reduced ALP activity. Mechanistically, HuR stabilized LRP6 mRNA and promoted its translation by binding to the 3'UTR of LRP6 mRNA, leading to activation of the downstream Wnt pathway. By this mechanism, osteoblastic differentiation of MC3T3-E1 cells was induced. In ovariectomized mice, overexpression of HuR alleviated osteoporosis-related phenotypes.

Conclusion

Overall, these data together support the promoting role of HuR in the osteoblastic differentiation, highlighting a potential novel strategy for osteoporosis treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-03073-w.

The effects and mechanism of paeoniflorin in promoting osteogenic differentiation of MC3T3-E1

Background

The incidence of osteoporosis and osteoporotic fractures is increasing every year. Traditional Chinese Medicine (TCM) can shed new light on the treatment of osteoporosis. This study aimed to explore the role and mechanism of paeoniflorin in promoting osteogenic differentiation of an osteoblast precursor cell line (MC3T3-E1).

Methods

MC3T3-E1 cells were cultured in osteogenic induction medium (OIM) and OIM combined with different concentrations of paeoniflorin. The optimal dose of paeoniflorin was assessed by a cell counting kit-8 (CCK-8) assay. Then, alkaline phosphatase (ALP) and Alizarin Red S (ARS) staining were performed to assess the osteogenic capacity of paeoniflorin. The transcription of osteogenic genes and the expression of osteogenic proteins were assessed by RT-PCR and Western blotting, respectively. The transcription of Wnt/β-catenin signaling pathway genes and proteins was assessed by RT-PCR and Western blotting, respectively. Finally, Dickkopf-1 (DKK-1), a Wnt/β-catenin signaling pathway inhibitor, was used to identify whether the Wnt/β-catenin signaling pathway was involved in the osteogenic differentiation of paeoniflorin. Osteoclastogenesis in RAW264.7 cells was identified by tartrate-resistant acid phosphatase (TRAP) staining.

Results

At concentrations ranging from 0.1 to 100 μM, paeoniflorin was not cytotoxic to MC3T3-E1 cells. Paeoniflorin significantly increased the osteogenic differentiation of MC3T3-E1 cells in a dose-dependent manner. Moreover, paeoniflorin significantly increased osteogenic differentiation gene and protein expression. Through bioinformatic analysis, paeoniflorin-affected genes were found to be involved in different signaling pathways, such as the Wnt/β-catenin signaling pathway. Paeoniflorin enhanced β-catenin and CyclinD1 expression compared with that of the control groups. DKK-1 partially reversed the promoting effects of paeoniflorin in promoting osteogenic differentiation of MC3T3-E1 cells. Moreover, paeoniflorin inhibited the osteoclastogenesis of RAW264.7 cells.

Conclusion

Paeoniflorin promotes osteogenic differentiation in MC3T3-E1 cells by regulating the Wnt/β-catenin pathway. Paeoniflorin is a potential therapeutic agent for the treatment of osteoporosis.

N-myc downstream regulated gene 1 suppresses osteoblast differentiation through inactivating Wnt/β-catenin signaling

Background

N-myc downstream regulated gene 1 (NDRG1) plays a role in a variety of biological processes including differentiation of osteoclasts. However, it is not known if and how NDRG1 regulates osteogenic differentiation of marrow stromal progenitor cells.

Methods

Gene expression profiling analysis was performed to study the expression level of Ndrg1 during osteogenic and adipogenic differentiation. Gain-of-function and/or loss-of function experiments were carried out to study the role of NDRG1 in the proliferation and differentiation of marrow stromal progenitor cells and the mechanism underlying the function was investigated. Finally, in vivo transfection of Ndrg1 siRNA was done and its effect on osteogenic and adipogenic differentiation in mice was explored.

Results

Gene expression profiling analysis revealed that NDRG1 level was regulated during osteogenic and adipogenic differentiation of progenitor cells. The functional experiments demonstrated that NDRG1 negatively regulated the cell growth, and reciprocally modulated the osteogenic and adipogenic commitment of marrow stromal progenitor cells, driving the cells to differentiate toward adipocytes at the expense of osteoblast differentiation. Moreover, NDRG1 interacted with low-density lipoprotein receptor-related protein 6 (LRP6) in the stromal progenitor cells and inactivated the canonical Wnt/β-catenin signaling cascade. Furthermore, the impaired differentiation of progenitor cells induced by Ndrg1 siRNA could be attenuated when β-catenin was simultaneously silenced. Finally, in vivo transfection of Ndrg1 siRNA to the marrow of mice prevented the inactivation of canonical Wnt signaling in the BMSCs of ovariectomized mice, and ameliorated the reduction of osteoblasts on the trabeculae and increase of fat accumulation in the marrow observed in the ovariectomized mice.

Conclusion

This study has provided evidences that NDRG1 plays a role in reciprocally modulating osteogenic and adipogenic commitment of marrow stromal progenitor cells through inactivating canonical Wnt signaling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02714-5.

Carfilzomib alleviated osteoporosis by targeting PSME1/2 to activate Wnt/β-catenin signaling

Osteoporosis (OP) is characterized by decreased bone mineral density and impaired bone strength. Carfilzomib (CFZ) is a new-generation proteasome inhibitor and has been found to affect bone metabolism. However, the effect and mechanism of CFZ on OP has not been investigated systematically. In this study, we found that protein levels of proteasome activator subunit 1/2 (PSME1/2) increased in OP, and accumulated mostly in osteoblasts and osteoclasts. Treatment with PSME1/2 recombinant protein inhibited osteogenesis and promoted osteoclast formation in vitro. Also, PSME1/2 inhibited the expression of β-catenin protein, resulting in limitation of Wnt/β-catenin signaling. CFZ inhibited PSME1 and PSME2 proteasome activities and increased β-catenin protein level, resulting in the translocation of β-catenin to the nucleus and activation of canonical Wnt/β-catenin signaling, further promoting osteogenesis and inhibiting osteoclastic differentiation. In vivo, we conducted ovariectomy (OVX) to create a model of OVX-induced postmenopausal OP in mice. When analyzed by micro-CT scanning, enhancement of bone mineral density, bone volume, trabecular number, and thickness was seen in the CFZ-treated mice. Also, we noticed increased osteogenesis and decreased osteoclastogenesis, diminished expression of PSME1 and PSME2 and activated Wnt/β-catenin signaling in bone sections from OP mice treated with CFZ. Overall, our data indicated that PSME1/2 may serve as new targets for the treatment of OP, and targeting PSME1/2 with CFZ provides a candidate therapeutic molecule for postmenopausal OP.

Wnt7b Inhibits Osteoclastogenesis via AKT Activation and Glucose Metabolic Rewiring

The imbalance between bone formation and bone resorption causes osteoporosis, which leads to severe bone fractures. It is known that increases in osteoclast numbers and activities are the main reasons for increasing bone resorption. Although extensive studies have investigated the regulation of osteoclastogenesis of bone marrow macrophages (BMMs), new pharmacological avenues still need to be unveiled for clinical purpose. Wnt ligands have been widely demonstrated as stimulators of bone formation; however, the inhibitory effect of the Wnt pathway in osteoclastogenesis is largely unknown. Here, we demonstrate that Wnt7b, a potent Wnt ligand that enhances bone formation and increases bone mass, also abolishes osteoclastogenesis in vitro. Importantly, enforced expression of Wnt in bone marrow macrophage lineage cells significantly disrupts osteoclast formation and activity, which leads to a dramatic increase in bone mass. Mechanistically, Wnt7b impacts the glucose metabolic process and AKT activation during osteoclastogenesis. Thus, we demonstrate that Wnt7b diminishes osteoclast formation, which will be beneficial for osteoporosis therapy in the future.

Integrating genome-wide association and transcriptome prediction model identifies novel target genes for osteoporosis

In this study, we integrated large-scale GWAS summary data and used the predicted transcriptome-wide association study method to discover novel genes associated with osteoporosis. We identified 204 candidate genes, which provide novel clues for understanding the genetic mechanism of osteoporosis and indicate potential therapeutic targets.

INTRODUCTION

Osteoporosis is a highly polygenetic disease characterized by low bone mass and deterioration of the bone microarchitecture. Our objective was to discover novel candidate genes associated with osteoporosis.

METHODS

To identify potential causal genes of the associated loci, we investigated trait-gene expression associations using the transcriptome-wide association study (TWAS) method. This method directly imputes gene expression effects from genome-wide association study (GWAS) data using a statistical prediction model trained on GTEx reference transcriptome data. We then performed a colocalization analysis to evaluate the posterior probability of biological patterns: associations characterized by a single causal variant or multiple distinct causal variants. Finally, a functional enrichment analysis of gene sets was performed using the VarElect and CluePedia tools, which assess the causal relationships between genes and a disease and search for potential gene's functional pathways. The osteoporosis-associated genes were further confirmed based on the differentially expressed genes profiled from mRNA expression data of bone tissue.

RESULTS

Our analysis identified 204 candidate genes, including 154 genes that have been previously associated with osteoporosis, 50 genes that have not been previously discovered. A biological function analysis found that 20 of the candidate genes were directly associated with osteoporosis. Further analysis of multiple gene expression profiles showed that 15 genes were differentially expressed in patients with osteoporosis. Among these, SLC11A2, MAP2K5, NFATC4, and HSP90B1 were enriched in four pathways, namely, mineral absorption pathway, MAPK signaling pathway, Wnt signaling pathway, and PI3K-Akt signaling pathway, which indicates a causal relationship with the occurrence of osteoporosis.

CONCLUSIONS

We demonstrated that transcriptome fine-mapping identifies more osteoporosis-related genes and provides key insight into the development of novel targeted therapeutics for the treatment of osteoporosis.

Integrative Analysis of LGR5/6 Gene Variants, Gut Microbiota Composition and Osteoporosis Risk in Elderly Population

Objective: This study aimed to explore the relationships between the common variants of R-spondin/Wnt signaling genes, gut microbiota composition, and osteoporosis (OP) risk in elderly Chinese Han population.

Design: Dual-energy X-ray absorptiometry was used to obtain the OP-associated measurements at multiple skeleton sites among all 1,168 participants. Genotyping data was obtained by using the next-generation sequencing in the discovery stage (n = 400, 228 OP patients) and SNPscan technology in the replication stage (n = 768, 356 OP patients). Bioinformatic analysis was performed to provide more evidence for the genotype-OP associations. The 16S ribosomal RNA gene high-throughput sequencing technology was adopted to explore OP-associated gut microbiota variations.

Results: The genetic variants of rs10920362 in the LGR6 gene (P-FDR = 1.19 × 10^–6) and rs11178860 in the LGR5 gene (P-FDR = 1.51 × 10^–4) were found to associate with OP risk significantly. Several microbial taxa were associated with the BMDs and T-scores at multiple skeleton sites. The associations between rs10920362 and BMD-associated microbiota maintained significance after adjusting confounders. The rs10920362 CT/TT genotype associated with a decreased relative abundance of Actinobacteria (β = −1.32, P < 0.001), Bifidobacteriaceae (β = −1.70, P < 0.001), and Bifidobacterium (β = −1.70, P < 0.001) compared to the CC genotype.

Conclusion: Our findings suggested that the variants loci of LGR6 may be associate with OP pathogenesis via gut microbiota modifications. The relationship between host genetics and gut microbiome provides new perspectives about OP prevention and treatment.

Targeting Filamin A alleviates ovariectomy-induced bone loss in mice via the WNT/β-catenin signaling pathway

Osteoporosis (OP) is a worldwide prevalent chronic metabolic bone disease, causing by a disruption of the balance between bone resorption and formation. Estrogen deficiency and aging are the main causes for disturbances in bone remodeling activity and bone loss, however, the mechanisms underlying bone remodeling regulation require clarification if novel targets for OP treatment are to be identified. In this investigation, we showed that filamin A (FLNA) accumulated in osteoblasts (OBs) and osteoclasts (OC) in bone from human OP samples, and mice with age-related and postmenopausal OP. FLNA negatively modulated in vitro osteogenic differentiation and positively promoted RANKL-induced osteoclastic differentiation. Mechanistically, FLNA interacted with low-density lipoprotein receptor-related proteins 6 (LRP6) to inhibit β-catenin expression, and enhanced nuclear factor of activated T cell c1 (NFATc1)-dependent osteoclastogenic gene expression to inhibit osteogenesis, and promote osteoclastogenesis. Inhibiting FLNA with calpeptin activated WNT/β-catenin signaling, resulting in prominent protective effects of bone loss in ovariectomy (OVX)-induced postmenopausal OP mice. Our findings revealed that FLNA not only participated in OP pathogenesis, but could be a new target to stimulate bone formation and inhibit bone resorption. Targeting FLNA with calpeptin may be a promising therapeutic approach for postmenopausal OP in the future.

Effects of sclerostin antibody on bone healing

Promoting bone healing after a fracture has been a frequent subject of research. Recently, sclerostin antibody (Scl-Ab) has been introduced as a new anabolic agent for the treatment of osteoporosis. Scl-Ab activates the canonical Wnt (cWnt)-β-catenin pathway, leading to an increase in bone formation and decrease in bone resorption. Because of its rich osteogenic effects, preclinically, Scl-Ab has shown positive effects on bone healing in rodent models; researchers have reported an increase in bone mass, mechanical strength, histological bone formation, total mineralized callus volume, bone mineral density, neovascularization, proliferating cell nuclear antigen score, and bone morphogenic protein expression at the fracture site after Scl-Ab administration. In addition, in a rat critical-size femoral-defect model, the Scl-Ab-treated group demonstrated a higher bone healing rate. On the other hand, two clinical reports have researched Scl-Ab in bone healing and failed to show positive effects in the femur and tibia. This review discusses why Scl-Ab appears to be effective in animal models of fracture healing and not in clinical cases.

The Development of Molecular Biology of Osteoporosis

Osteoporosis is one of the major bone disorders that affects both women and men, and causes bone deterioration and bone strength. Bone remodeling maintains bone mass and mineral homeostasis through the balanced action of osteoblasts and osteoclasts, which are responsible for bone formation and bone resorption, respectively. The imbalance in bone remodeling is known to be the main cause of osteoporosis. The imbalance can be the result of the action of various molecules produced by one bone cell that acts on other bone cells and influence cell activity. The understanding of the effect of these molecules on bone can help identify new targets and therapeutics to prevent and treat bone disorders. In this article, we have focused on molecules that are produced by osteoblasts, osteocytes, and osteoclasts and their mechanism of action on these cells. We have also summarized the different pharmacological osteoporosis treatments that target different molecular aspects of these bone cells to minimize osteoporosis.

Wnt-C59 inhibits proinflammatory cytokine expression by reducing the interaction between β-catenin and NF-κB in LPS-stimulated epithelial and macrophage cells

Dysregulation of the Wnt pathway causes various diseases including cancer, Parkinson’s disease, Alzheimer’s disease, schizophrenia, osteoporosis, obesity and chronic kidney diseases. The modulation of dysregulated Wnt pathway is absolutely necessary. In the present study, we evaluated the anti-inflammatory effect and the mechanism of action of Wnt-C59, a Wnt signaling inhibitor, in lipopolysaccharide (LPS)-stimulated epithelial cells and macrophage cells. Wnt-C59 showed a dose-dependent anti-inflammatory effect by suppressing the expression of proinflammatory cytokines including IL6, CCL2, IL1A, IL1B, and TNF in LPS-stimulated cells. The dysregulation of the Wnt/β-catenin pathway in LPS stimulated cells was suppressed by Wnt-C59 treatment. The level of β-catenin, the executor protein of Wnt/β-catenin pathway, was elevated by LPS and suppressed by Wnt-C59. Overexpression of β-catenin rescued the suppressive effect of Wnt-C59 on proinflammatory cytokine expression and nuclear factor-kappa B (NF-κB) activity. We found that the interaction between β-catenin and NF-κB, measured by co-immunoprecipitation assay, was elevated by LPS and suppressed by Wnt-C59 treatment. Both NF-κB activity for its target DNA binding and the reporter activity of NF-κB-responsive promoter showed identical patterns with the interaction between β-catenin and NF-κB. Altogether, our findings suggest that the anti-inflammatory effect of Wnt-C59 is mediated by the reduction of the cellular level of β-catenin and the interaction between β-catenin and NF-κB, which results in the suppressions of the NF-κB activity and proinflammatory cytokine expression.

Phosphocreatine Promotes Osteoblastic Activities in H2O2-Induced MC3T3-E1 Cells by Regulating SIRT1/FOXO1/PGC-1α Signaling Pathway

BACKGROUND

Osteoporosis, characterized by bone loss, usually occurs with the increased bone resorption and decreased bone formation. H₂O₂-induced MC3T3-E1 cells are commonly used for the study of osteoblastic activities, which play a crucial role in bone formation.

OBJECTIVE

This study aimed to investigate the effects of Phosphocreatine (PCr) on the osteoblastic activities in H₂O₂-induced MC3T3-E1 cells and elaborate on the possible molecular mechanism.

METHODS

The Osteoprotegerin (OPG)/Receptor Activator of NF-κB Ligand (RANKL) ratio and osteogenic markers were detected to investigate the effects of PCr on osteoblastic activities, and the osteoblastic apoptosis was detected using Hochest staining. Moreover, oxidative stress, Adenosine Triphosphate (ATP) generation and the expression of Sirtuin 1 (SIRT1), Forkhead Box O 1 (FOXO1) and Peroxisome Proliferator-Activated Receptor Γ Coactivator-1α (PGC-1α) were also examined to uncover the possible molecular mechanism in H₂O₂-induced MC3T3-E1 cells.

RESULT

The results showed that PCr promoted the osteoblastic differentiation by increasing the expression levels of osteogenic markers of Alkaline Phosphatase (ALP) and Runt-related transcription factor 2 (Runx2), as well as increased the OPG/RANKL ratio and suppressed the osteoblastic apoptosis in H₂O₂-induced MC3T3-E1 cells. Moreover, treatment with PCr suppressed reactive oxygen species (ROS) over-generation and promoted the ATP production as well as increased the PGC-1α, FOXO1 and SIRT1 protein expression levels in H₂O₂-induced MC3T3-E1 cells.

CONCLUSION

PCr treatment could promote osteoblastic activities via suppressing oxidative stress and increasing the ATP generation in H₂O₂-induced MC3T3-E1 cells. In addition, the positive effects of PCr on osteoblasts might be regulated by SIRT1/FOXO1/ PGC-1α signaling pathway.

Identification of the specific microRNAs and competitive endogenous RNA mechanisms in osteoporosis

Objective

Osteoporosis and osteoarthritis are metabolic skeletal disorders. This study aimed to identify specific networks of competitive endogenous RNA (ceRNA) in osteoporosis that differ from those in osteoarthritis.

Methods

The dataset GSE74209 was downloaded from the Gene Expression Omnibus, and differentially expressed microRNAs (DEmiRNAs) in osteoporotic samples and osteoarthritic samples were identified. After predicting target genes and linked long noncoding (lnc)RNAs, ceRNA networks of DEmiRNAs were constructed. The nodes that overlapped between ceRNA networks and the Comparative Toxicogenomics Database were selected as key candidates.

Results

Fifteen DEmiRNAs (including 2 downregulated and 13 upregulated miRNAs) were identified in osteoporotic samples versus osteoarthritic samples; these targeted 161 genes and linked to 60 lncRNAs. The ceRNA network consisted of 6 DEmiRNAs, 63 target genes, and 53 lncRNAs. After searching the Comparative Toxicogenomics Database and mining the literature, 2 lncRNAs (MALAT1 and NEAT1), 2 DEmiRNAs (hsa-miR-32-3p, downregulated; and hsa-miR-22-3p, upregulated) and 6 genes (SP1, PTEN, ESR1, ERBB3, CSF1R, and CDK6) that relate to cell death, growth, and differentiation were identified as key candidates separating osteoporosis from osteoarthritis.

Conclusions

Two miRNA–ceRNA networks (including NEAT1/MALAT1-hsa-miR-32-3p-SP1/FZD6 and NEAT1/MALAT1-hsa-miR-22-3p-PTEN/ESR1/ERBB3/CSF1R/CDK6) might have crucial and specific roles in osteoporosis.

Chemotherapy-elicited exosomal miR-378a-3p and miR-378d promote breast cancer stemness and chemoresistance via the activation of EZH2/STAT3 signaling

Background

Not all breast cancer (BC) patients who receive neoadjuvant chemotherapy achieve a pathologic complete response (pCR), but the reasons for this are unknown. Previous studies have shown that exosomes produced in the tumor microenvironment in response to chemotherapy promote a chemotherapy-resistant phenotype in tumors. However, the role of BC chemotherapy-elicited exosomes in regulating chemoresistance is poorly understood.

Methods

Using commercial kits, serum exosomes were extracted from patients before neoadjuvant chemotherapy, after one cycle of chemotherapy and after four cycles of chemotherapy consisting of doxorubicin (DOX) and paclitaxel (PTX). Their miRNAs were sequenced, and the correlation between the sequencing results and chemotherapy effects was further verified by RT-qPCR using patient serum exosomes. Cell Counting Kit-8 (CCK-8) was used to detect chemosensitivity. Stemness was assessed by CD44+/CD24- population analysis and mammosphere formation assays. Chromatin immunoprecipitation (ChIP) experiments were performed to verify the binding of signal transducer and activator of transcription 3 (STAT3) to the promoter of miRNAs.

Results

Here, we provide clinical evidence that chemotherapy-elicited exosomal miR-378a-3p and miR-378d are closely related to the chemotherapy response and that exosomes produced by BC cells after stimulation with DOX or PTX deliver miR-378a-3p and miR-378d to neighboring cells to activate WNT and NOTCH stemness pathways and induce drug resistance by targeting Dickkopf 3 (DKK3) and NUMB. In addition, STAT3, which is enhanced by zeste homolog 2 (EZH2), bound to the promoter regions of miR-378a-3p and miR-378d, thereby increasing their expression in exosomes. More importantly, chemotherapeutic agents combined with the EZH2 inhibitor tazemetostat reversed chemotherapy-elicited exosome-induced drug resistance in a nude mouse tumor xenograft model.

Conclusion

This study revealed a novel mechanism of acquired chemoresistance whereby chemotherapy activates the EZH2/STAT3 axis in BC cells, which then secrete chemotherapy-elicited exosomes enriched in miR-378a-3p and miR-378d. These exosomes are absorbed by chemotherapy-surviving BC cells, leading to activation of the WNT and NOTCH stem cell pathways via the targeting of DKK3 and NUMB and subsequently resulting in drug resistance. Therefore, blocking this adaptive mechanism during chemotherapy may reduce the development of chemotherapy resistance and maximize the therapeutic effect.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-01901-1.

Detecting causal relationship between metabolic traits and osteoporosis using multivariable Mendelian randomization

By adopting the extension approaches of Mendelian randomization, we successfully detected and prioritized the potential causal risk factors for BMD traits, which might provide us novel insights for treatment and intervention into bone-related complex traits and diseases.

INTRODUCTION

Osteoporosis (OP) is a common metabolic skeletal disease characterized by reduced bone mineral density (BMD). The identified SNPs for BMD can only explain approximately 10% of the variability, and very few causal factors have been identified so far.

METHODS

The Mendelian randomization (MR) approach enables us to assess the potential causal effect of a risk factor on the outcome by using genetic IVs. By using extension methods of MR-multivariable MR (mvMR) and MR based on Bayesian model averaging (MR-BMA)-we intend to estimate the causal relationship between fifteen metabolic risk factors for BMD and try to prioritize the most potential causal risk factors for BMD.

RESULTS

Our analysis identified three risk factors T2D, FG, and HCadjBMI for FN BMD; four risk factors FI, T2D, HCadjBMI, and WCadjBMI for FA BMD; and three risk factors FI, T2D, and HDL cholesterol for LS BMD, and all risk factors were causally associated with heel BMD except for triglycerides and WCadjBMI. Consistent with the mvMR results, MR-BMA confirmed those risk factors as top risk factors for each BMD trait individually.

CONCLUSIONS

By combining MR approaches, we identified the potential causal risk factors for FN, FA, LS, and heel BMD individually and we also prioritized and ranked the potential causal risk factors for BMD, which might provide us novel insights for treatment and intervention into bone-related complex traits and diseases.

Disparate bone anabolic cues activate bone formation by regulating the rapid lysosomal degradation of sclerostin protein

The downregulation of sclerostin in osteocytes mediates bone formation in response to mechanical cues and parathyroid hormone (PTH). To date, the regulation of sclerostin has been attributed exclusively to the transcriptional downregulation of the Sost gene hours after stimulation. Using mouse models and rodent cell lines, we describe the rapid, minute-scale post-translational degradation of sclerostin protein by the lysosome following mechanical load and PTH. We present a model, integrating both new and established mechanically and hormonally activated effectors into the regulated degradation of sclerostin by lysosomes. Using a mouse forelimb mechanical loading model, we find transient inhibition of lysosomal degradation or the upstream mechano-signaling pathway controlling sclerostin abundance impairs subsequent load-induced bone formation by preventing sclerostin degradation. We also link dysfunctional lysosomes to aberrant sclerostin regulation using human Gaucher disease iPSCs. These results reveal how bone anabolic cues post-translationally regulate sclerostin abundance in osteocytes to regulate bone formation.

Lnc13728 facilitates human mesenchymal stem cell adipogenic differentiation via positive regulation of ZBED3 and downregulation of the WNT/β-catenin pathway

Background

Obesity has received increasing attention because of its widespread worldwide occurrence and many threats to health. Human adipose-derived mesenchymal stem cells (hADSCs) are a critical source of adipocytes. Long noncoding RNAs (lncRNAs) play pivotal roles in cell fate determination and differentiation. The objective of the present study was to identify and investigate the function and regulatory mechanism of lncRNAs on adipogenic differentiation of hADSCs.

Methods

We used lncRNA arrays to identify the prominent differentially expressed lncRNAs before and after hADSC adipogenic differentiation and verified their biological function through antisense oligonucleotide knockdown or lentivirus overexpression. The adipogenic differentiation of hADSCs was assessed by oil red O staining as well as the mRNA and protein levels of adipogenic marker genes through qRT-PCR and western blot. Bioinformatic tool LncPro and immunofluorescence was performed to uncover the interaction between lnc13728 and ZBED3. WNT/β-catenin signaling pathway was evaluated by western blot and immunofluorescence.

Results

The lncRNA arrays showed that lnc13728 expression was significantly upregulated after hADSC adipogenic differentiation and was correlated positively with the expression of the adipogenesis-related genes in human adipose tissue. Lnc13728 knockdown in hADSCs suppressed the expression of the adipogenesis-related genes at both mRNA and protein level and weakened lipid droplet production. Accordingly, lnc13728 overexpression enhanced hADSC adipogenic differentiation. Beyond that, lnc13728 co-localized with ZBED3 in the cytoplasm and regulated its expression positively. Downregulating ZBED3 had a negative effect on adipogenic differentiation, while the expression of WNT/β-catenin signaling pathway-related proteins was upregulated.

Conclusions

Lnc13728 promotes hADSC adipogenic differentiation possibly by positively regulating the expression of ZBED3 which plays a role in inhibiting the WNT/β-catenin pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02250-8.

Prostate cancer-secreted CCN3 uses the GSK3β and β-catenin pathways to enhance osteogenic factor levels in osteoblasts

Prostate cancer osteoblastic bone metastases are incurable and associated with chronic bone pain and a high mortality rate. Osteoclast-targeting drugs intended to prevent skeletal-related events associated with prostate cancer bone metastases do not prolong overall survival. Improved understanding of the bone-derived factors that contribute to prostate cancer osteoblastic bone metastases is required to design treatments that will improve morbidities and overall survival. Activated osteoblasts stimulate prostate cancer growth in bone. In this study, we report that prostate cancer conditioned medium (CM) promoted bone morphogenetic protein (BMP)-2, -4 and -7 production and the expression of osteogenic transcription factors Runx2 and osterix in osteoblasts. Treating the prostate cancer CM with antibody against CCN3 (nephroblastoma-overexpressed), a cysteine-rich protein that belongs to the CCN family, reduced all of these increases. Incubation of osteoblasts with CCN3 facilitated phosphorylation of GSK3β and β-catenin. GSK3β and β-catenin inhibitors or siRNAs all abolished CCN3-induced promotion of BMPs, Runx2 and osterix expression in osteoblasts. Our results indicate that prostate cancer-secreted CCN3 enhances BMP, Runx2 and osterix expression in osteoblasts via the GSK3β and β-catenin signaling pathways. This understanding of the role played by CCN3 in osteoblastic prostate bone metastasis may lead to more efficient targeted therapies.

Running Against the Wnt: How Wnt/β-Catenin Suppresses Adipogenesis

Mesenchymal stem cells (MSCs) give rise to adipocytes, osteocytes, and chondrocytes and reside in various tissues, including bone marrow and adipose tissue. The differentiation choices of MSCs are controlled by several signaling pathways, including the Wnt/β-catenin signaling. When MSCs undergo adipogenesis, they first differentiate into preadipocytes, a proliferative adipocyte precursor cell, after which they undergo terminal differentiation into mature adipocytes. These two steps are controlled by the Wnt/β-catenin pathway, in such a way that when signaling is abrogated, the next step in adipocyte differentiation can start. This sequence suggests that the main role of Wnt/β-catenin signaling is to suppress differentiation while increasing MSC and preadipocytes cell mass. During later steps of MSC differentiation, however, active Wnt signaling can promote osteogenesis instead of keeping the MSCs undifferentiated and proliferative. The exact mechanisms behind the various functions of Wnt signaling remain elusive, although recent research has revealed that during lineage commitment of MSCs into preadipocytes, Wnt signaling is inactivated by endogenous Wnt inhibitors. In part, this process is regulated by histone-modifying enzymes, which can lead to increased or decreased Wnt gene expression. The role of Wnt in adipogenesis, as well as in osteogenesis, has implications for metabolic diseases since Wnt signaling may serve as a therapeutic target.

Osteoblastic Wnt1 regulates periosteal bone formation in adult mice

Compelling clinical data together with genetically modified mouse models have demonstrated that Wnt1 is a key Wnt ligand in bone metabolism, regulating both osteoblast activity and osteoclast differentiation. We have previously shown that deletion of Wnt1 in limb mesenchymal cells leads to severe ostepenic bone phenotype and spontaneous fractures very early after birth. However, the function of Wnt1 in mature skeleton remained unknown. To investigate the role of Wnt1 specifically in adult bone metabolism, we generated an osteoblast lineage-targeted inducible Wnt1 knockout mouse model using tetracycline-controlled Osterix-Cre mouse line (Osx-Cre). In this model, the Cre recombinase expression is suppressed by administering doxycycline (Dox) in drinking water. As expected, Wnt1_Osx^-/- mice without Dox developed spontaneous fractures early by 3 weeks of age due to severe trabecular and cortical osteopenia. Administration of Dox to Wnt1_Osx-Dox^-/- and control mice until 4 weeks of age suppressed Wnt1 deletion and completely prevented the fractures. Withdrawal of Dox led to deletion in Wnt1 allele but the fracture incidence progressively decreased in Wnt1_Osx-Dox^-/- mice at 8 or 12 weeks of age (4 and 8 weeks after Dox withdrawal). Interestingly, deletion of Wnt1 at 4 weeks of age resulted only in a modest and transient trabecular osteopenia that was more pronounced in females and was normalized by 12 weeks of age. However, diaphyseal cortical bone mass and cortical thickness in the femurs were significantly decreased in Wnt1_Osx-Dox^-/- mice of both genders. Mechanisticly, this was due to impaired periosteal bone formation. Based on our data, in addition to its essential role in early skeletal growth, Wnt1 is an important regulator of modeling-based bone formation and cortical thickness in adult mice.

Do polyunsaturated fatty acids protect against bone loss in our aging and osteoporotic population?

Age-related bone loss is inevitable in both men and women and there will soon be more people of extreme old age than ever before. Osteoporosis is a common chronic disease and as the proportion of older people, rate of obesity and the length of life increases, a rise in age-related degenerating bone diseases, disability, and prolonged dependency is projected. Fragility fractures are one of the most severe complications associated with both primary and secondary osteoporosis and current treatment strategies target weight-bearing exercise and pharmacological intervention, both with limited long-term success. Obesity and osteoporosis are intimately interrelated, and diet is a variable that plays a significant role in bone regeneration and repair. The Western Diet is characterized by its unhealthy components, specifically excess amounts of saturated fat intake. This review examines the impact of saturated and polyunsaturated fatty acid consumption on chronic inflammation, osteogenesis, bone architecture, and strength and explores the hypothesis that dietary polyunsaturated fats have a beneficial effect on osteogenesis, reducing bone loss by decreasing chronic inflammation, and activating bone resorption through key cellular and molecular mechanisms in our aging population. We conclude that aging, obesity and a diet high in saturated fatty acids significantly impairs bone regeneration and repair and that consumption of ω-3 polyunsaturated fatty acids is associated with significantly increased bone regeneration, improved microarchitecture and structural strength. However, ω-6 polyunsaturated fatty acids were typically pro-inflammatory and have been associated with an increased fracture risk. This review suggests a potential role for ω-3 fatty acids as a non-pharmacological dietary method of reducing bone loss in our aging population. We also conclude that contemporary amendments to the formal nutritional recommendations made by the Food and Nutrition Board may be necessary such that our aging population is directly considered.

Diffuse Idiopathic Skeletal Hyperostosis (DISH) in Type 2 Diabetes: A New Imaging Possibility and a New Biomarker

We performed a cross-sectional study to investigate the prevalence of Diffuse Idiopathic Skeletal Hyperostosis (DISH) through Dual-Energy X-ray absorptiometry (DXA) Vertebral Fracture Assessment (VFA) in a group of post-menopausal women with Type 2 Diabetes Mellitus (T2DM). We also explored several biomarkers of bone turnover metabolism, including Wnt pathway modulators. DXA-VFA was performed to detect the presence of DISH. Serum samples were collected from all patients at the time of study recruitment. 16 different serum biomarkers were tested between the two subgroups. Given the exploratory nature of the study, we did not adjust for multiplicity. At VFA analysis, among 96 individuals enrolled in the study 20 (20.8%) showed features of DISH. No statistically significant difference was found for BMD values, between the DISH and NO-DISH subgroups. Concerning blood biomarkers, DISH patients showed a significant difference only in the sclerostin serum levels (32 vs 35.5 pmol/L, for the DISH and NO-DISH subgroup, respectively; p = 0.010). After adjustment for confounding factors, sclerostin serum levels remained significantly lower in DISH group (p = 0.002). We demonstrated a non-negligible prevalence of DISH in a population of post-menopausal women affected by T2DM and suggested low serum sclerostin as a possible key feature associated with DISH presence. In addition, we propose DXA-VFA analysis, whose radiation dose is considerably lower than conventional radiography, as a viable diagnostic and prognostic mean to obtain data not only on bone health, but also for the screening for DISH in subjects at risk.

Osteoporosis: Mechanism, Molecular Target and Current Status on Drug Development

CDATA[Osteoporosis is a pathological loss of bone mass due to an imbalance in bone remodeling where osteoclast-mediated bone resorption exceeds osteoblast-mediated bone formation resulting in skeletal fragility and fractures. Anti-resorptive agents, such as bisphosphonates and SERMs, and anabolic drugs that stimulate bone formation, including PTH analogues and sclerostin inhibitors, are current treatments for osteoporosis. Despite their efficacy, severe side effects and loss of potency may limit the long term usage of a single drug. Sequential and combinational use of current drugs, such as switching from an anabolic to an anti-resorptive agent, may provide an alternative approach. Moreover, there are novel drugs being developed against emerging new targets such as Cathepsin K and 17β-HSD2 that may have less side effects. This review will summarize the molecular mechanisms of osteoporosis, current drugs for osteoporosis treatment, and new drug development strategies.

Deciphering the Relevance of Bone ECM Signaling

Bone mineral density, a bone matrix parameter frequently used to predict fracture risk, is not the only one to affect bone fragility. Other factors, including the extracellular matrix (ECM) composition and microarchitecture, are of paramount relevance in this process. The bone ECM is a noncellular three-dimensional structure secreted by cells into the extracellular space, which comprises inorganic and organic compounds. The main inorganic components of the ECM are calcium-deficient apatite and trace elements, while the organic ECM consists of collagen type I and noncollagenous proteins. Bone ECM dynamically interacts with osteoblasts and osteoclasts to regulate the formation of new bone during regeneration. Thus, the composition and structure of inorganic and organic bone matrix may directly affect bone quality. Moreover, proteins that compose ECM, beyond their structural role have other crucial biological functions, thanks to their ability to bind multiple interacting partners like other ECM proteins, growth factors, signal receptors and adhesion molecules. Thus, ECM proteins provide a complex network of biochemical and physiological signals. Herein, we summarize different ECM factors that are essential to bone strength besides, discussing how these parameters are altered in pathological conditions related with bone fragility.

Metaanalysis Reveals Genetic Correlates of Osteoporosis Pathogenesis

OBJECTIVE

Osteoporosis is a growing healthcare burden. By identifying osteoporosis-promoting genetic variations, we can spotlight targets for new pharmacologic therapies that will improve patient outcomes. In this metaanalysis, we analyzed mesenchymal stem cell (MSC) biomarkers in patients with osteoporosis.

METHODS

We employed our Search Tag Analyze Resource for the Gene Expression Omnibus (STARGEO) platform to conduct a metaanalysis to define osteoporosis pathogenesis. We compared 15 osteoporotic and 14 healthy control MSC samples. We then analyzed the genetic signature in Ingenuity Pathway Analysis.

RESULTS

The top canonical pathways identified that were statistically significant included the serine peptidase inhibitor kazal type 1 pancreatic cancer pathway, calcium signaling, pancreatic adenocarcinoma signaling, axonal guidance signaling, and glutamate receptor signaling. Upstream regulators involved in this disease process included ESR1, dexamethasone, CTNNβ1, CREB1, and ERBB2.

CONCLUSION

Although there has been extensive research looking at the genetic basis for inflammatory arthritis, very little literature currently exists that has identified genetic pathways contributing to osteoporosis. Our study has identified several important genes involved in osteoporosis pathogenesis including ESR1, CTNNβ1, CREB1, and ERBB2. ESR1 has been shown to have numerous polymorphisms, which may play a prominent role in osteoporosis. The Wnt pathway, which includes the CTNNβ1 gene identified in our study, plays a prominent role in bone mass regulation. Wnt pathway polymorphisms can increase susceptibility to osteoporosis. Our analysis also suggests a potential mechanism for ERBB2 in osteoporosis through Semaphorin 4D (SEMA4D). Our metaanalysis identifies several genes and pathways that can be targeted to develop new anabolic drugs for osteoporosis treatment.

5-Phenyl-1,3,4-oxadiazol-2(3H)-ones Are Potent Inhibitors of Notum Carboxylesterase Activity Identified by the Optimization of a Crystallographic Fragment Screening Hit

Carboxylesterase Notum is a negative regulator of the Wnt signaling pathway. There is an emerging understanding of the role Notum plays in disease, supporting the need to discover new small-molecule inhibitors. A crystallographic X-ray fragment screen was performed, which identified fragment hit 1,2,3-triazole 7 as an attractive starting point for a structure-based drug design hit-to-lead program. Optimization of 7 identified oxadiazol-2-one 23dd as a preferred example with properties consistent with drug-like chemical space. Screening 23dd in a cell-based TCF/LEF reporter gene assay restored the activation of Wnt signaling in the presence of Notum. Mouse pharmacokinetic studies with oral administration of 23dd demonstrated good plasma exposure and partial blood-brain barrier penetration. Significant progress was made in developing fragment hit 7 into lead 23dd (>600-fold increase in activity), making it suitable as a new chemical tool for exploring the role of Notum-mediated regulation of Wnt signaling.

Daphnetin ameliorates glucocorticoid-induced osteoporosis via activation of Wnt/GSK-3β/β-catenin signaling

Glucocorticoids have been widely used in multiple inflammatory and autoimmune diseases. However, long-term glucocorticoid therapy may result in osteoporosis. The present study aimed to evaluate the potential therapeutic effects and investigate the underlying mechanisms of Daphnetin (Daph) on glucocorticoid-induced osteoporosis (GIOP). In vivo, male Sprague Dawley rats were intramuscularly injected with dexamethasone (DEX) to induce GIOP and Daph was given intraperitoneally. Bone histological changes, mineral content, microstructure parameters and bone turnover markers were detected. Gut microbiota composition and intestinal barrier function were further assessed. In vitro, MC3T3-E1 pre-osteoblasts were treated with DEX and the abilities of Daph on osteoblast proliferation, differentiation and mineralization were assessed. A Wnt signaling inhibitor, XAV939, was added additionally to evaluate the effect of Daph on Wnt signaling. The results showed that in vivo, Daph increased the DEX-induced reduction in body weight gain, bone mineral content and microstructure parameters and restored the levels of bone turnover markers in GIOP rats. In vitro, Daph promoted osteoblast proliferation, differentiation and mineralization in DEX-treated MC3T3-E1 pre-osteoblasts. Moreover, Daph activated the Wnt/GSK-3β/β-catenin signaling pathway. XAV939 successfully abolished the beneficial effects of Daph on GIOP in vitro. Besides, Daph showed improvement on gut microbiota disorder and intestinal barrier dysfunction post GIOP. Collectively, these data demonstrated that Daph effectively ameliorates GIOP and the possible mechanism may be that Daph activated Wnt/GSK-3β/β-catenin signaling.