Wnt signalling in osteoblasts regulates expression of the receptor activator of NFkappaB ligand and inhibits osteoclastogenesis in vitro

UPLC-Q-TOF/MS characterization of efficacy substances on osteoblasts differentiation and function in rat serum after administration of Wang-Bi tablet

Wang-Bi tablet (WB) is popularly used for the treatment of rheumatoid arthritis. However, few studies have been carried out on its active ingredients and mechanism. In this study, the effect of WB medicated serum on the changes in differentiation and function in osteoblast was investigated, the results showed that WB induced the production of ALP and mineralized nodules to promote the final maturation of osteoblasts and enhance the function of osteoblasts. The potential mechanism may that WB significantly inhibits gene expressions of RANKL and miR-141, up-regulates the gene expressions of RUNX2 and OPG, decreases expression of DKK-1 and increases levels of β-catenin protein to promote the activation of Wnt/β-catenin signaling pathways, which enhances osteogenesis and bone repair function. To investigate which compounds contributed to the activity and mechanisms, a total of 138 compounds were characterized from WB, and 13 parent molecules and eight metabolites in rat serum were rapidly characterized by UPLC-Q-TOF/MS. Total glycosides of paeony, loganin, α-linolenic acid, linoleic acid and naringin from WB may contribute to the actions on osteoblasts according to our study and literature review. Our research provides a method to explore the bioactive ingredients and action mechanisms of WB.

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

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

Protective effects of Wang-Bi tablet on bone destruction in collagen-induced arthritis by regulating osteoclast-osteoblast functions

ETHNOPHARMACOLOGICAL RELEVANCE

Wang-bi tablet (WB) consists of 17 traditional Chinese medicines and has been used for treating rheumatoid arthritis (RA) in China for many years, however, its pharmacologic mechanism is not clear.

AIM OF STUDY

The aim of this study was to investigate the therapeutic effect of WB on collagen-induced mouse arthritis and explored the underlying mechanism.

MATERIALS AND METHODS

DBA/1 mice were used to establish a type II collagen-induced arthritis (CIA) model. From the day of arthritis onset, mice were treated daily by gavage with either total glucosides of paeony (TGP, 0.37  g/kg/d) or WB at a lower (1.11  g/kg/d, WBL) or higher dose of (3.33  g/kg/d, WBH) for 8 weeks. The severity of arthritis, levels of cytokines and the activation of signaling pathways were determined.

RESULTS

Our results revealed that WB treatment effectively alleviated inflammatory symptoms and prevented bone erosions and joint destructions. It obviously decreased the serum concentration of pro-inflammatory cytokines TNF-α, IL-6 and IL-17α, while increased the concentration of anti-inflammatory cytokine IL-10. Interestingly, the proportion of splenic Treg cells were increased significantly. In vitro experiments showed that WB inhibited the differentiation of osteoclasts. Consistently, the mRNA levels of tartrate-resistant acid phosphatase (TRAP) and cathepsin K (CtsK), and the activation of NF-κB and JAK-STAT3 signaling pathways in the paws of CIA mice were inhibited by WB treatment. On the other hand, up-regulation of osteogenic genes Runx2, Osterix mRNA, and activation of Wnt/β-catenin signaling pathway along with a decreased receptor activator of nuclear factor κB ligand (RANKL) expression were found in WB treated mice.

CONCLUSION

Our results suggest that the therapeutic effect of Wang-bi tablet could be attributed to its inhibitory activity on NF-κB and STAT3 signaling pathway-mediated osteoclast differentiation, and its enhancement on Wnt/β-catenin signaling pathway-mediated osteoblast functions.

Inverse correlation between trabecular bone volume and bone marrow adipose tissue in rats treated with osteoanabolic agents

There is currently an unmet clinical need for improved treatments for skeletal diseases such as osteoporosis and cancer-induced bone disease. This is due in part to a paucity of novel targets and an incomplete understanding of the mechanisms of action for established therapies. We defined the effects of anabolic treatments on bone and the bone marrow adipocyte (BMA). Sclerostin-neutralizing antibodies (Scl-Ab), romosozumab, human parathyroid hormone (hPTH, 1-34), and hPTH/hPTHrP analogues (e.g. teriparatide and abaloparatide) stimulate bone formation and have been studied in clinical trials for severe osteoporosis. In this study, eight-week-old male and female rats were administered vehicle, Scl-Ab (3 mg/kg or 50 mg/kg) weekly, or hPTH (1-34) (75 μg/kg) daily for 4 or 26 weeks. Histological analyses of distal femura were performed using a novel ImageJ method for trabecular bone and bone marrow adipose tissue (BMAT). Adipocyte number, circumference, and total adipose area were compared within the tissue area (T.Ar) or the marrow area (Ma.Ar), (defined as the T.Ar minus the trabecular bone area). After 26 weeks of treatment, a significant inverse correlation between bone and tissue adiposity (total adipocyte area divided by T.Ar) were observed in males and females (p < 0.0001). However, there were no significant correlations between bone and marrow adiposity (total adipocyte area divided by Ma.Ar) for either sex after 26 weeks of treatments. Scl-Ab treatments also resulted in no effect on adipocytes based on marrow adiposity for either sex after 26 weeks. However, chronic hPTH treatments significantly reduced adipocyte number and adiposity within the T.Ar and within the Ma.Ar in males. Overall, our data suggest that with long-term treatment, Scl-Abs decrease total tissue adiposity mainly by increasing trabecular bone, resulting in an overall reduction in the space in which adipocytes can reside. These findings were determined by developing and comparing two different methods of assessment of the marrow cavity, defined to either include or exclude trabecular bone. Thus, researchers should consider which adiposity measurement is more informative and relevant for their studies. Overall, our findings should help design improved therapies or combination treatments to target a potential new contributor to bone diseases: the bone marrow adipocyte.

The Glycogen Synthase Kinase-3β Inhibitor LSN 2105786 Promotes Zebrafish Fin Regeneration

The Wnt pathway has been shown to regulate bone homeostasis and to influence some bone disease states. We utilized a zebrafish model system to study the effects of a synthetic, orally bioavailable glycogen synthase kinase-3β (GSK3β) inhibitor LSN 2105786, which activates Wnt signaling during bone healing and embryogenesis. GSK3β inhibitor treatment was used to phenocopy GSK3β morpholino oligonucleotide (MO) knockdown in zebrafish embryos. Human and zebrafish synthetic mRNA injection were similarly effective at rescue of GSK3β MO knockdown. During caudal fin regeneration, bony rays are the first structure to differentiate in zebrafish fins, providing a useful model to study bone healing. Caudal fin regeneration experiments were conducted using various concentrations of a GSK3β inhibitor, examining duration and concentration dependence on regenerative outgrowth. Experiments revealed continuous low concentration (4-5 nM) treatment to be more effective at increasing regeneration than intermittent dosing. Higher concentrations inhibited fin growth, perhaps by excessive stimulation of differentiation programs. Increased Wnt responsive gene expression and differentiation were observed in response to GSK3b inhibitor treatment. Activating Wnt signaling also increased cell proliferation and osteoblast differentiation in fin regenerates. Together, these data indicate that bone healing in zebrafish fin regeneration was improved by activating Wnt signaling using GSK3b inhibitor treatment. In addition, caudal fin regeneration is useful to evaluate dose-dependent pharmacological efficacy in bone healing, various dosing regimens and possible toxicological effects of compounds.

Bone Disease in Mastocytosis

Systemic mastocytosis can give very different bone pictures: from osteosclerosis to osteoporosis. Osteoporosis is one of the most frequent manifestations particularly in adults and the most clinical relevant. It is often complicated by a high recurrence of mainly vertebral fragility fractures. The main factor of bone loss is the osteoclast with a relative or absolute predominance of bone resorption. The RANK-RANKL pathway seems of key importance, but histamine and other cytokines also play a significant role in the process. The predominance of resorption made bisphosphonates, as anti-resorptive drugs, the most rational treatment of bone involvement in systemic mastocytosis.

Therapeutic Irradiation: Consequences for Bone and Bone Marrow Adipose Tissue

Radiotherapy continues to be one of the most accepted medical treatments for cancer. Localized irradiation is the most common treatment for prostate, pancreatic, rectal, cervical and endometrial malignancies. Conventional localized fractions are total doses of 30-62Gy at 1.8-2Gy per fraction, with administration of ~60Gy often used for tumor ablation. However, even the lowest dose of localized irradiation exposure can result in adverse complications to adjacent organs, tissues, and vessels, which absorb a portion of the treatment. Skeletal complications are common amongst cancer patients undergoing these localized treatments. Irradiation exposure causes deterioration to the overall quantity and quality of bone by interfering with the trabecular architecture through increased osteoclast activity and decreased osteoblast activity. Irradiation-induced bone damage parallels adipocyte infiltration of the bone marrow (BM) resulting in compositional alterations of the microenvironment that may further affect bone quality and disease state. There may also be direct effects of irradiation on the BM adipocyte/pre-adipocyte, although in vitro findings do not always agree and cellular response is dependent on irradiation dosage. Hematopoietic cells also become apoptotic upon irradiation, which causes a range of skeletal effects. Bone loss leaves patients at a greater risk for osteopenia, osteoporosis, osteonecrosis, and skeletal fractures that drastically reduce quality of life. Osteoanabolic agents stimulate bone formation and reduce fracture risk in patients with low bone density; thus, osteoanabolic or anti-resorptive agents may be useful co-treatments with irradiation. This review discusses these topics and proposes further research directions using novel or combination therapies to enhance bone health during irradiation.

Dkk1 involvement and its potential as a biomarker in pancreatic ductal adenocarcinoma

Dickkopf-1 (Dkk1)'s dysregulation has been implicated in the pathogenesis of a variety of cancers. It is part of the Dkk family of proteins that includes Dkk2, Dkk3 and Dkk4. This family of secreted proteins shares similar conserved cysteine domains and inhibits the Wnt/b-catenin pathway by causing proteasomal B-catenin degradation, inducing apoptosis, and preventing cell proliferation. Pancreatic ductal adenocarcinoma (PDAC) is the 4th leading cause of cancer mortality in the United States due to the late stage of diagnosis and the limited effectiveness of current therapy. Dkk1 is found increased in PADC patients' specimens and serum. Dkk1 can be a promising biomarker specific to PDAC, which has the potential to increase PDAC survival rates through improving early stage detection and monitoring progression compared to current biomarker gold standards. In addition, recent studies suggest that Dkk1 could be an excellent target for cancer immunotherapy. Interestingly, Dkk1-CKAP4-PI3K/AKT signal pathway also plays role in pancreatic cancer cell proliferation. In this review, we present the multiple mechanisms of Dkk1 in PDAC studied thus far and explore its function, regulation, and clinical applications in gynecological cancers including pancreatic ductal adenocarcinoma (PDAC), breast, ovarian, cervical, and endometrial cancer. Further research into Dkk1's mechanism and use as a diagnostic tool, alone or in combination with other biomarkers, could prove clinically useful for better understanding the pathology of PDAC and improving its early detection and treatment.

TIMP Loss Activates Metalloproteinase-TNFα-DKK1 Axis To Compromise Wnt Signaling and Bone Mass

Deregulated proteolysis invariably underlies most human diseases including bone pathologies. Metalloproteinases constitute the largest of the five protease families, and the metzincin metalloproteinases are inhibited by the four tissue inhibitors of metalloproteinase called TIMPs. We hypothesized that Timp genes are essential for skeletal homeostasis. We bred individual Timp knockout mice to generate unique mouse models, the quadruple Timp null strain (QT) as well as mice harboring only a single Timp3 allele (QT3^+/- ). QT mice are grossly smaller and exhibit a dramatic reduction of trabeculae in long bones by μCT imaging with a corresponding increase in metalloproteinase activity. At the cellular level, Timp deficiency compromised differentiation markers, matrix deposition and mineralization in neonatal osteoblasts from calvariae, as well as the fibroblastic colony-forming unit (CFU-F) capacity of bone marrow-derived stromal cells. In contrast, we observed that osteoclasts were overactive in the Timp null state, consistent with the noted excessive bone resorption of QT bones. Immunohistochemistry (IHC) and immunofluorescence (IF) analyses of bone sections revealed higher Cathepsin K and RANKL signals upon Timp loss. Seeking the molecular mechanism, we identified abnormal TNFα bioactivity to be a central event in Timp-deficient mice. Specifically, TNFα triggered induction of the Wnt signaling inhibitor Dkk1 in the osteoblasts at the mRNA and protein levels, with a simultaneous increase in RANKL. Neutralizing TNFα antibody was capable of rescuing the induction of Dkk1 as well as RANKL. Therefore, the generation of novel Timp-deficient systems allowed us to uncover the essential and collective function of TIMP proteins in mammalian long-bone homeostasis. Moreover, our study discovers a functional TIMP/metalloproteinase-TNFα-Dkk1/RANKL nexus for optimal control of the bone microenvironment, which dictates coexistence of the osteoblast and osteoclast lineages. © 2018 American Society for Bone and Mineral Research.

Iron-enriched diet contributes to early onset of osteoporotic phenotype in a mouse model of hereditary hemochromatosis

Osteoporosis is associated with chronic iron overload secondary to hereditary hemochromatosis (HH), but the causative mechanisms are incompletely understood. The main objective of this study was to investigate the role of dietary iron on osteoporosis, using as biological model the Hfe-KO mice, which have a systemic iron overload. We showed that these mice show an increased susceptibility for developing a bone loss phenotype compared to WT mice, which can be exacerbated by an iron rich diet. The dietary iron overload caused an increase in inflammation and iron incorporation within the trabecular bone in both WT and Hfe-KO mice. However, the osteoporotic phenotype was only evident in Hfe-KO mice fed the iron-enriched diet. This appeared to result from an imbalance between bone formation and bone resorption driven by iron toxicity associated to Hfe-KO and confirmed by a decrease in bone microarchitecture parameters (identified by micro-CT) and osteoblast number. These findings were supported by the observed downregulation of bone metabolism markers and upregulation of ferritin heavy polypeptide 1 (Fth1) and transferrin receptor-1 (Tfrc), which are associated with iron toxicity and bone loss phenotype. In WT mice the iron rich diet was not enough to promote a bone loss phenotype, essentially due to the concomitant depression of bone resorption observed in those animals. In conclusion the dietary challenge influences the development of osteoporosis in the HH mice model thus suggesting that the iron content in the diet may influence the osteoporotic phenotype in systemic iron overload conditions.

Sclerosteosis: Report of type 1 or 2 in three Indian Tamil families and literature review

Sclerosteosis (SOST) refers to two extremely rare yet similar skeletal dysplasias featuring a diffusely radiodense skeleton together with congenital syndactyly. SOST1 is transmitted as an autosomal recessive (AR) trait and to date caused by ten homozygous loss-of-function mutations within the gene SOST that encodes the inhibitor of Wnt-mediated bone formation, sclerostin. SOST2 is transmitted as an autosomal dominant (AD) or AR trait and to date caused by one heterozygous or two homozygous loss-of-function mutation(s), respectively, within the gene LRP4 that encodes the sclerostin interaction protein, low-density lipoprotein receptor-related protein 4 (LRP4). Herein, we investigated two teenagers and one middle-aged man with SOST in three families living in the state of Tamil Nadu in southern India. Next generation sequencing of their genomic DNA using our high bone density gene panel revealed SOST1 in the teenagers caused by a unique homozygous nonsense SOST mutation (c.129C > G, p.Tyr43X) and SOST2 in the man caused by homozygosity for one of the two known homozygous missense LRP4 mutations (c.3508C > T, p.Arg1170Trp). He becomes the fourth individual and the first non-European recognized with SOST2. His clinical course was milder than the life-threatening SOST1 demonstrated by the teenagers who suffered blindness, deafness, and raised intracranial pressure, yet his congenital syndactyly was more striking by featuring bony fusion of digits. All three patients were from consanguineous families and heterozygosity for the SOST mutation was documented in the mothers of both teenagers. Thus, on the endogamous genetic background of Indian Tamils, SOST1 from sclerostin deficiency compared to SOST2 from LRP4 deactivation is a more severe and life-threatening disorder featuring complications due to osteosclerosis of especially the skull. In contrast, the syndactyly of SOST2 is particularly striking by involving bony fusion of some digits. Both the SOST and LRP4 mutations in this ethnic population likely reflect genetic founders.

Postnatal Skeletal Deletion of Dickkopf-1 Increases Bone Formation and Bone Volume in Male and Female Mice, Despite Increased Sclerostin Expression

The Wnt antagonist Dickkopf-1 (Dkk1) is a negative regulator of osteoblast function and bone mass. However, because of the lack of appropriate models, many aspects of its role in the regulation of postnatal bone turnover and its cellular source have remained unknown. In this study, we deleted Dkk1 postnatally and in different cell types using various Cre-drivers (Rosa26-ERT2-Cre, Osx-cre, Dmp1-Cre) and assessed to which extent cells of the osteoblastic lineage contribute to the effects of Dkk1 on bone turnover and homeostasis. Female and male mice were examined at 12 weeks of age. Mice with a global or cell type-specific deletion of Dkk1 showed a two- to threefold higher bone volume compared with their Cre-negative littermates. The mineral apposition rate and the bone formation rate were increased two- to fourfold in all three mouse lines, despite a significant increase in systemic and skeletal levels of sclerostin. Dkk1 deletion further reduced the number of osteoclasts about twofold, which was accompanied by a strong decrease in the receptor activator of nuclear factor-κB ligand/osteoprotegerin mRNA ratio in femoral bone. Despite similar increases in bone mass, the deletion of Dkk1 in osterix-expressing cells reduced circulating Dkk1 significantly (males, -79%; females, -77%), whereas they were not changed in Dkk1^fl/fl ;Dmp1-Cre mice. However, both lines showed significantly reduced Dkk1 mRNA levels in bone. In summary, we show that lack of Dkk1 in cells of the osteoblastic lineage leads to high bone mass with increased bone formation, despite increased levels of sclerostin. Moreover, the majority of systemic Dkk1 appears to originate from osteoprogenitors but not from mature osteoblasts or osteocytes. Nevertheless, the amount of Dkk1 produced locally by more mature osteogenic cells is sufficient to modulate bone mass. Thus, this study highlights the importance of local Wnt signaling on postnatal bone homeostasis. © 2018 American Society for Bone and Mineral Research.

Multiple Myeloma and Bone: The Fatal Interaction

Multiple myeloma (MM) is the second-most-common hematologic malignancy and the most frequent cancer to involve bone. MM bone disease (MMBD) has devastating consequences for patients, including dramatic bone loss, severe bone pain, and pathological fractures that markedly decrease the quality of life and impact survival of MM patients. MMBD results from excessive osteoclastic bone resorption and persistent suppressed osteoblastic bone formation, causing lytic lesions that do not heal, even when patients are in complete and prolonged remission. This review discusses the cellular and molecular mechanisms that regulate the uncoupling of bone remodeling in MM, the effects of MMBD on tumor growth, and potential therapeutic approaches that may prevent severe bone loss and repair damaged bone in MM patients.

Circulating levels of sclerostin are associated with cardiovascular mortality

Cardiovascular diseases are a health problem throughout the world, especially in people with diabetes. The identification of cardiovascular disease biomarkers can improve risk stratification. Sclerostin is a modulator of the Wnt/β-catenin signalling pathway in different tissues, and it has recently been linked to vascular biology. The current study aimed to evaluate the relationship between circulating sclerostin levels and cardiovascular and non-cardiovascular mortality in individuals with and without type 2 diabetes. We followed up a cohort of 130 participants (mean age 56.8 years; 48.5% females; 75 with type 2 diabetes; 46 with prevalent cardiovascular disease) in which serum sclerostin levels were measured at the baseline. Time to death (both of cardiovascular and non-cardiovascular causes) was assessed to establish the relationship between sclerostin and mortality. We found that serum sclerostin concentrations were significantly higher in patients with prevalent cardiovascular disease (p<0.001), and independently associated with cardiovascular mortality (p = 0.008), showing sclerostin to be a stronger predictor of mortality than other classical risk factors (area under the curve = 0.849 vs 0.823). The survival analysis showed that an increase of 10 pmol/L in the serum sclerostin level resulted in a 31% increase in cardiovascular mortality. However, no significant association was observed between sclerostin levels and non-cardiovascular mortality (p = 0.346).

From these results, we conclude that high sclerostin levels are related to mortality due to cardiovascular causes. The clinical implication of these findings is based on the possible use of serum sclerostin as a new biomarker of cardiovascular mortality risk in order to establish preventive strategies.

YAP promotes osteogenesis and suppresses adipogenic differentiation by regulating β-catenin signaling

YAP (yes-associated protein) is a transcriptional factor that is negatively regulated by Hippo pathway, a conserved pathway for the development and size control of multiple organs. The exact function of YAP in bone homeostasis remains controversial. Here we provide evidence for YAP’s function in promoting osteogenesis, suppressing adipogenesis, and thus maintaining bone homeostasis. YAP is selectively expressed in osteoblast (OB)-lineage cells. Conditionally knocking out Yap in the OB lineage in mice reduces cell proliferation and OB differentiation and increases adipocyte formation, resulting in a trabecular bone loss. Mechanistically, YAP interacts with β-catenin and is necessary for maintenance of nuclear β-catenin level and Wnt/β-catenin signaling. Expression of β-catenin in YAP-deficient BMSCs (bone marrow stromal cells) diminishes the osteogenesis deficit. These results thus identify YAP-β-catenin as an important pathway for osteogenesis during adult bone remodeling and uncover a mechanism underlying YAP regulation of bone homeostasis.

A key regulatory gene both promotes bone formation and suppresses production of fat-storing bone marrow cells, thus supporting the key process of bone remodeling. As adults, our bones are in a constant state of flux, constantly being dissolved and rebuilt to maintain a steady state known as homeostasis. An international team led by Wen-Cheng Xiong, of Case Western Reserve University, Cleveland, Ohio, studied the role of the gene ‘yes-associated protein’ (YAP), a transcription factor (gene controlling the activity of other genes). Using mice, they found that YAP is essential for osteogenesis, and prevents adipocyte (fat-storing cell) formation. Without a functional YAP gene, mice experienced a loss of a softer type of bone known as trabecular bone. The molecular pathways controlled by YAP may thus be important for bone remodeling in vertebrates.

Bisphosphonates hinder osteoblastic/osteoclastic differentiation in the maxillary sinus mucosa-derived stem cells

OBJECTIVES

Although bisphosphonates (BPs) are known to be associated with osteonecrosis of the maxilla, the precise effects of BPs on bone metabolism in human maxillary sinus mucosal cells (HMSMCs) are not yet known. The purposes of this study were to examine the effects of the BPs zoledronate (ZOL) and alendronate (ALN) on osteoblastic and osteoclastic differentiation in HMSMCs and to investigate the signaling pathways involved.

MATERIALS AND METHODS

The effects of ZOL and ALN were assessed for osteoblast differentiation by alkaline phosphatase (ALP) activity, alizarin red staining, and RT-PCR for genes encoding Runx2 and osterix. Receptor activator of nuclear factor-κB ligand (RANKL)-mediated osteoclast differentiation in bone marrow macrophages (BMMs) was also examined.

RESULTS

ZOL and ALN both suppressed osteoblastic differentiation, as evidenced by their effects on ALP activity, mineralization nodule formation, and the mRNA expression levels of osteoblastic transcript factors. The RANKL/osteoprotegerin ratio in HMSMCs was increased by ALN, whereas ZOL had the opposite effect. Conditioned medium obtained from ALN-treated HMSMCs stimulated osteoclast formation and upregulated NFATc1 expression, whereas conditioned medium from ZOL-treated cells did not. ALN was more cytotoxic and stimulated apoptosis more strongly than ZOL. BPs decreased the protein levels of the non-canonical Wnt signaling protein Wnt5a and calmodulin-dependent kinase II. Moreover, recombinant human Wnt5a reversed the effects of BPs on osteoblastic and osteoclastic differentiation.

CONCLUSION

This study is the first demonstration that BPs exert negative effects on osteoblastic and osteoclastic processes via the non-canonical Wnt pathway in HMSMSCs.

CLINICAL RELEVANCE

It suggests that patients taking BPs during the period of maxillary sinus lifting and amentation should be given special attention.

Repression of MAP3K1 expression and JNK activity by canonical Wnt signaling

Morphogenesis is a complex and highly coordinated process orchestrated by temporal spatial activity of developmental pathways. How the different pathways interact to guide the developmental program remains an intriguing and open question. MAP3K1-JNK and Wnt are signaling pathways crucial for embryonic eyelid closure, an epithelial morphogenetic event conserved in mammals. Here we used a mouse model of eyelid development and genetic and biochemistry tools to investigate the relationships between the two pathways. We found that Wnt activation repressed MAP3K1 expression. Using Axin-LacZ reporter mice, spatial Wnt activity was detected in the leading edge of the developing eyelid. Conditional knockout of Wntless (Wls) in ocular surface ectoderm blocked eyelid formation, and significantly increased MAP3K1 expression in eyelid cells at the nasal canthus region. Conversely, knockout of Dkk2, encoding a canonical Wnt antagonist, resulted in an increase of Wnt activity in cells at the upper eyelid margin near the nasal canthus. Up-regulation of Wnt signaling in the Dkk2-knockout embryos corresponded to down-regulation of MAP3K1 expression. In vitro data showed that Wnt3a treatment decreased MAP3K1 promoter activity, whereas activation of Wnt by lithium chloride inhibited MAP3K1 expression, and attenuated MAP3K1-mediated JNK activity. Our data identify a unique signal crosstalk between Wnt signaling and the MAP3K1-JNK pathway in epithelial morphogenesis.

Targeting sphingosine-1-phosphate lyase as an anabolic therapy for bone loss

Sphingosine-1-phosphate (S1P) signaling influences bone metabolism, but its therapeutic potential in bone disorders has remained unexplored. We show that raising S1P levels in adult mice through conditionally deleting or pharmacologically inhibiting S1P lyase, the sole enzyme responsible for irreversibly degrading S1P, markedly increased bone formation, mass and strength and substantially decreased white adipose tissue. S1P signaling through S1P₂ potently stimulated osteoblastogenesis at the expense of adipogenesis by inversely regulating osterix and PPAR-γ, and it simultaneously inhibited osteoclastogenesis by inducing osteoprotegerin through newly discovered p38-GSK3β-β-catenin and WNT5A-LRP5 pathways. Accordingly, S1P₂-deficient mice were osteopenic and obese. In ovariectomy-induced osteopenia, S1P lyase inhibition was as effective as intermittent parathyroid hormone (iPTH) treatment in increasing bone mass and was superior to iPTH in enhancing bone strength. Furthermore, lyase inhibition in mice successfully corrected severe genetic osteoporosis caused by osteoprotegerin deficiency. Human data from 4,091 participants of the SHIP-Trend population-based study revealed a positive association between serum levels of S1P and bone formation markers, but not resorption markers. Furthermore, serum S1P levels were positively associated with serum calcium , negatively with PTH , and curvilinearly with body mass index. Bone stiffness, as determined through quantitative ultrasound, was inversely related to levels of both S1P and the bone formation marker PINP, suggesting that S1P stimulates osteoanabolic activity to counteract decreasing bone quality. S1P-based drugs should be considered as a promising therapeutic avenue for the treatment of osteoporotic diseases.

The serum level of Dickkopf-1 in patients with rheumatoid arthritis: A systematic review and meta-analysis

OBJECTIVE

Dickkopf-1 (DKK-1) is an endogenous inhibitor of canonical Wnt pathway that was implicated in the pathogenesis of rheumatoid arthritis (RA), but the serum levels of DKK-1 in RA were inconsistent among studies. Therefore, we conducted a meta-analysis to systematically evaluate the relationship between serum DKK-1 levels and RA.

METHODS

PubMed, Web of Science and Cochrane Library were comprehensively retrieved till 1 January 2018 for pertinent studies. The pooled standard mean differences (SMDs) of serum DKK-1 levels were calculated according to the random effects model.

RESULTS

Nine original studies containing 1305 RA patients and 504 healthy controls were included in the meta-analysis. The pooled SMD of serum DKK-1 between RA patients and healthy controls was 0.79 (95% CI = 0.11 to 1.48, Z = 2.28 and P = 0.023), indicating a significantly higher serum level of DKK-1 in RA patients.

CONCLUSION

Serum level of DKK-1 is elevated in patients with RA compared to healthy controls, suggesting an important role of DKK-1 in the pathogenesis and treatment of RA.

Biology and treatment of myeloma related bone disease

Myeloma bone disease (MBD) is the most common complication of multiple myeloma (MM), resulting in skeleton-related events (SREs) such as severe bone pain, pathologic fractures, vertebral collapse, hypercalcemia, and spinal cord compression that cause significant morbidity and mortality. It is due to an increased activity of osteoclasts coupled to the suppressed bone formation by osteoblasts. Novel molecules and pathways that are implicated in osteoclast activation and osteoblast inhibition have recently been described, including the receptor activator of nuclear factor-kB ligand/osteoprotegerin pathway, activin-A and the wingless-type signaling inhibitors, dickkopf-1 (DKK-1) and sclerostin. These molecules interfere with tumor growth and survival, providing possible targets for the development of novel drugs for the management of lytic disease in myeloma but also for the treatment of MM itself. Currently, bisphosphonates are the mainstay of the treatment of myeloma bone disease although several novel agents such as denosumab and sotatercept appear promising. This review focuses on recent advances in MBD pathophysiology and treatment, in addition to the established therapeutic guidelines.

Fine Tuning of Canonical Wnt Stimulation Enhances Differentiation of Pluripotent Stem Cells Independent of β-Catenin-Mediated T-Cell Factor Signaling

The canonical Wnt/β-catenin pathway is crucial for early embryonic patterning, tissue homeostasis, and regeneration. While canonical Wnt/β-catenin stimulation has been used extensively to modulate pluripotency and differentiation of pluripotent stem cells (PSCs), the mechanism of these two seemingly opposing roles has not been fully characterized and is currently largely attributed to activation of nuclear Wnt target genes. Here, we show that low levels of Wnt stimulation via ectopic expression of Wnt1 or administration of glycogen synthase kinase-3 inhibitor CHIR99021 significantly increases PSC differentiation into neurons, cardiomyocytes and early endodermal intermediates. Our data indicate that enhanced differentiation outcomes are not mediated through activation of traditional Wnt target genes but by β-catenin's secondary role as a binding partner of membrane bound cadherins ultimately leading to the activation of developmental genes. In summary, fine-tuning of Wnt signaling to subthreshold levels for detectable nuclear β-catenin function appears to act as a switch to enhance differentiation of PSCs into multiple lineages. Our observations highlight a mechanism by which Wnt/β-catenin signaling can achieve dosage dependent dual roles in regulating self-renewal and differentiation. Stem Cells 2018;36:822-833.

Treadmill running exercise prevents senile osteoporosis and upregulates the Wnt signaling pathway in SAMP6 mice

This study examined the effects of different exercise intensities and durations on bone mineral density (BMD) and bone strength in senescence-accelerated mouse prone 6 (SAMP6) and determined the involvement of the Wnt signaling pathway in exercise-induced osteogenesis. Three-month-old male SAMP6 mice were randomly assigned to different speeds of treadmill running exercise representing low, medium and high intensity, with the duration of five and nine weeks, respectively. We showed that medium-intensity exercise had positive effects on skeletal health, including BMD and bone strength, and the efficacy was higher than that of low-intensity exercise. Interestingly, high-intensity exercise can maintain or even increase bone strength, despite its negative effects on bone mass. Nine weeks of exercise was superior to 5 weeks of exercise, particularly for low-intensity exercise. Furthermore, these effects of exercise-induced osteogenesis are accompanied by activation of the Wnt signaling pathway. Taken together, these results suggest that the positive effects of exercise on osteoporosis prevention are intensity and duration-dependent, and may involve the regulation of Wnt signaling pathways.

Calycosin Orchestrates Osteogenesis of Danggui Buxue Tang in Cultured Osteoblasts: Evaluating the Mechanism of Action by Omics and Chemical Knock-out Methodologies

Danggui Buxue Tang (DBT), an ancient Chinese herbal decoction commonly used to mitigate menopausal osteoporosis, contains two herbs: Astragali Radix (AR) and Angelicae Sinensis Radix (ASR). The exact efficacy of individual chemical(s) within DBT, or in any herbal mixture, is hard to be revealed. Calycosin and ferulic acid have been reported to be the predominant chemicals found within DBT, and its roles in regulating osteoblastic differentiation have been proposed here. To probe the roles of calycosin and ferulic acid, these chemicals were specifically depleted from the DBT extracts. Here, calycosin-depleted DBT (DBT_Δcal) and ferulic acid-depleted DBT (DBT_Δfa), generated by semi-preparative HPLC, were coupled with RNA-seq and metabolomics analyses to reveal the synergistic functions of individual chemicals within a complex herbal mixture. The expressions of osteogenic differentiation markers were significantly increased under the treatments of DBT and DBT_Δfa. The DBT-induced genes were markedly reduced in the absent of calycosin, i.e., DBT_Δcal. In cultured osteoblasts, the DBT-activated Wnt/β-catenin and MAPK/Erk and signaling pathways were greatly affected when calycosin was depleted. By metabolomics analysis in DBT-treated osteoblasts, the profile of metabolites triggered by DBT_Δcal showed distinction to that of DBT and/or DBT_Δfa. Thus, our findings indicated that calycosin, rather than ferulic acid, could be an indispensable chemical in DBT to orchestrate multi-components of DBT in achieving maximal osteogenic properties.

Role of sclerostin and dkk1 in bone remodeling in type 2 diabetic patients

PURPOSE

This study aimed to investigate the role of sclerostin and dkk1 in the bone metabolism of type 2 diabetic patients.

METHODS

This cross-sectional study included 95 inpatients with type 2 diabetes mellitus. We divided the patients into three groups (i.e., the normal bone mineral density (BMD) group, osteopenia group and osteoporosis group) based on their different BMD levels and measured the serum levels of sclerostin, dkk1, 25-hydroxyvitamin D₃ (25OHD₃), bone turnover markers and other biochemical data in each group.

RESULTS

Significantly increased levels of serum sclerostin and dkk1 were found in the osteoporosis group, even when the male and female cohorts were considered separately. Ordinal logistic regression analysis suggested that the levels of serum sclerostin were independently associated with the presence of osteopenia and osteoporosis after adjusting for age, gender and 25OHD₃ (sclerostin: OR = 1.02, p = 0.001). The areal BMDs were negatively correlated with the levels of serum sclerostin and dkk1 and positively correlated with 25OHD₃. In addition, age, glycosylated hemoglobin and serum sclerostin levels were predictors for N-terminal propeptide of type 1 procollagen and serum dkk1 levels were the only predictors for crosslinked carboxyterminal telopeptide in type 1 collagen.

CONCLUSIONS

The sclerostin and dkk1 levels increased in conjunction with the reduction of BMD, confirming that the Wnts, inhibited by sclerostin and dkk1, were potentially responsible for bone fragility in type 2 diabetes patients with osteoporosis. Note that the serum sclerostin levels were predictors for bone formation, while the DKK1 levels predicted bone resorption.

Wnt Signaling in Hematological Malignancies

Leukemia and lymphoma are a wide encompassing term for a diverse set of blood malignancies that affect people of all ages and result in approximately 23,000 deaths in the United States per year (Siegel RL, Miller KD, Jemal A. Cancer statistics, 2016. CA Cancer J Clin. 2016;66(1):7-30.). Hematopoietic stem cells (HSCs) are tissue-specific stem cells at the apex of the hierarchy that gives rise to all of the terminally differentiated blood cells, through progressively restricted progenitor populations, a process that is known to be Wnt-responsive. In particular, the progenitor populations are subject to uncontrolled expansion during oncogenic processes, namely the common myeloid progenitor and common lymphoid progenitor, as well as the myeloblast and lymphoblast. Unregulated growth of these cell-types leads to mainly three types of blood cancers (i.e., leukemia, lymphoma, and myeloma), which frequently exhibit deregulation of the Wnt signaling pathway. Generally, leukemia is caused by the expansion of myeloid progenitors, leading to an overproduction of white blood cells; as such, patients are unable to make sufficient numbers of red blood cells and platelets. Likewise, an overproduction of lymphocytes leads to clogging of the lymph system and impairment of the immune system in lymphomas. Finally, cancer of the plasma cells in the blood is called myeloma, which also leads to immune system failure. Within each of these three types of blood cancers, there are multiple subtypes, usually characterized by their timeline of onset and their cell type of origin. Of these, 85% of leukemias are encompassed by the four most common diseases, that is, acute myeloid leukemia (AML), chronic myeloid leukemia (CML), acute lymphoblastic leukemia (ALL), and chronic lymphocytic leukemia (CLL); AML accounts for the majority of leukemia-related deaths (Siegel RL, Miller KD, Jemal A. Cancer statistics, 2016. CA Cancer J Clin. 2016;66(1):7-30.). Through understanding how HSCs are normally developed and maintained, we can understand how the normal functions of these pathways are disrupted during blood cancer progression; the Wnt pathway is important in regulation of both normal and malignant hematopoiesis. In this chapter, we will discuss the role of Wnt signaling in normal and aberrant hematopoiesis. Our understanding the relationship between Wnt and HSCs will provide novel insights into therapeutic targets.

Mammalian target of rapamycin as a therapeutic target in osteoporosis

The mechanistic target of rapamycin (mTOR) plays a key role in sensing and integrating large amounts of environmental cues to regulate organismal growth, homeostasis, and many major cellular processes. Recently, mounting evidences highlight its roles in regulating bone homeostasis, which sheds light on the pathogenesis of osteoporosis. The activation/inhibition of mTOR signaling is reported to positively/negatively regulate bone marrow mesenchymal stem cells (BMSCs)/osteoblasts-mediated bone formation, adipogenic differentiation, osteocytes homeostasis, and osteoclasts-mediated bone resorption, which result in the changes of bone homeostasis, thereby resulting in or protect against osteoporosis. Given the likely importance of mTOR signaling in the pathogenesis of osteoporosis, here we discuss the detailed mechanisms in mTOR machinery and its association with osteoporosis therapy.

Mechanisms of bone destruction in multiple myeloma

Osteolytic bone disease is a frequent complication of multiple myeloma, resulting in skeletal complications that are a significant cause of morbidity and mortality. It is the result of an increased activity of osteoclasts, which is not followed by reactive bone formation by osteoblasts. Recent studies have revealed novel molecules and pathways that are implicated in osteoclast activation and osteoblast inhibition. Among them, the most important include the receptor activator of nuclear factor-kappa B ligand/osteoprotegerin pathway, the macrophage inflammatory proteins and the activin-A that play a crucial role in osteoclast stimulation in myeloma, while the wingless-type (Wnt) signalling inhibitors (sclerostin and dickkopf-1) along with the growth factor independence-1 are considered the most important factors for the osteoblast dysfunction of myeloma patients. Finally, the role of osteocytes, which is the key cell for normal bone remodelling, has also revealed during the last years through their interaction with myeloma cells that leads to their apoptosis and the release of RANKL and sclerostin maintaining bone loss in these patients. This review focuses on the latest available data for the mechanisms of bone destruction in multiple myeloma.

Romosozumab for the treatment of osteoporosis

INTRODUCTION

Sclerostin, a glycoprotein produced primarily by osteocytes, blocks the canonical Wnt signaling bone formation pathway. Romosozumab is a humanized monoclonal antibody to sclerostin that binds to sclerostin, permitting the engagement of Wnt ligands with their co-receptors, resulting in an increase in bone formation and bone mineral density (BMD). Clinical studies with romosozumab have shown dramatic improvements in BMD at the spine and hip. Romosozumab is associated with improvement in bone strength through mechanisms that include increases in bone formation and, different from classical osteoanabolic agents, suppression of bone resorption. Areas covered: Herein, the authors highlight the available data on romosozumab for the treatment of osteoporosis. This includes the latest data on the efficacy, pharmacokinetics and pharmacodynamics as well as safety and tolerability data. Expert opinion: Monthly subcutaneous dosing of romosozumab reduces the risk of vertebral and clinical fractures in women with postmenopausal osteoporosis, with a favorable balance of benefits and risks. Romosozumab is a promising emerging anabolic agent with a novel mechanism of action that may expand the options for treating osteoporotic patients at high risk of fracture.

The role of stromal cells in inflammatory bone loss

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

In psoriatic arthritis Dkk-1 and PTH are lower than in rheumatoid arthritis and healthy controls

Psoriatic Arthritis (PsA) is characterized by bone erosive damage often associated with exuberant bone formation especially in enthesial sites. Dkk-1 and sclerostin are the main inhibitors of the WNT/β-catenin signaling pathway and play a key role in the regulation of both bone formation and resorption. We performed this study in order to compare the serum levels of the WNT-pathway regulators along with bone turnover markers (BTM) and parathyroid hormone (PTH) between three different groups: one group of female patients affected by PsA, one group of female patients affected by rheumatoid arthritis (RA), and healthy female controls (HC). This is a cross-sectional study including 33 patients with PsA classified with the CASPAR criteria, 35 HC, and 28 patients with RA classified with the ACR/EULAR 2010 criteria. Intact N-propeptide of type I collagen (PINP), C-terminal telopeptide of type I collagen (CTX-I), Dickkopf-related-protein 1 (Dkk-1), sclerostin, PTH, and 25OH-vitamin D serum levels were dosed. The PsA group showed significantly lower Dkk-1 levels when compared to the HC and RA groups. Dkk-1 in the RA group was significantly higher than HC. A similar trend was documented for PTH. In the PsA group, CTX-I was found to be lower than in both the RA and HC groups. This study demonstrated for the first time that Dkk-1 levels in PsA are lower than HC, in contrast with RA, in which they are increased. These results might contribute to explain the different bone involvement of the two different diseases.

Transglutaminases factor XIII-A and TG2 regulate resorption, adipogenesis and plasma fibronectin homeostasis in bone and bone marrow

Appropriate bone mass is maintained by bone-forming osteoblast and bone-resorbing osteoclasts. Mesenchymal stem cell (MSC) lineage cells control osteoclastogenesis via expression of RANKL and OPG (receptor activator of nuclear factor κB ligand and osteoprotegerin), which promote and inhibit bone resorption, respectively. Protein crosslinking enzymes transglutaminase 2 (TG2) and Factor XIII-A (FXIII-A) have been linked to activity of myeloid and MSC lineage cells; however, in vivo evidence has been lacking to support their function. In this study, we show in mice that TG2 and FXIII-A control monocyte-macrophage cell differentiation into osteoclasts as well as RANKL production in MSCs and in adipocytes. Long bones of mice lacking TG2 and FXIII-A transglutaminases, show compromised biomechanical properties and trabecular bone loss in axial and appendicular skeleton. This was caused by increased osteoclastogenesis, a cellular phenotype that persists in vitro. The increased potential of TG2 and FXIII-A deficient monocytes to form osteoclasts was reversed by chemical inhibition of TG activity, which revealed the presence of TG1 in osteoclasts and assigned different roles for the TGs as regulators of osteoclastogenesis. TG2- and FXIII-A-deficient mice had normal osteoblast activity, but increased bone marrow adipogenesis, MSCs lacking TG2 and FXIII-A showed high adipogenic potential and significantly increased RANKL expression as well as upregulated TG1 expression. Chemical inhibition of TG activity in the null cells further increased adipogenic potential and RANKL production. Altered differentiation of TG2 and FXIII-A null MSCs was associated with plasma fibronectin (FN) assembly defect in cultures and FN retention in serum and marrow in vivo instead of assembly into bone. Our findings provide new functions for TG2, FXIII-A and TG1 in bone cells and identify them as novel regulators of bone mass, plasma FN homeostasis, RANKL production and myeloid and MSC cell differentiation.

Monocytes, Macrophages, and Osteoclasts in Osteosarcoma

Macrophages appear to have a fundamental role in the pathogenesis of osteosarcoma. These highly diverse plastic cells are subdivided into classical or inflammatory macrophages known as M1 and alternative macrophages, which decrease inflammation and are reparative, called M2. Although primary and metastatic osteosarcomas are infiltrated with M2 macrophages, targeting the M1 macrophages with the immune adjuvant muramyl tripeptide phosphatidyl ethanolamine (MTP-PE) has been the greatest recent therapeutic advance in osteosarcoma. This discrepancy between the presence of M2 and activation of M1 macrophages is intriguing and is likely explained either by the plasticity of M1 and M2 macrophages or nonclassical patrolling monocytes (PMos). To date, MTP-PE has been approved in combination with chemotherapy for nonmetastatic osteosarcoma, but its use in metastatic tumors has not been investigated. In this review, we focus on macrophages, monocytes, and osteoclasts, their role in osteosarcoma, and the potential for targeting these cells in this disease.

TNFα Increases RANKL Expression via PGE₂-Induced Activation of NFATc1

Tumor necrosis factor α (TNFα) is known to upregulate the expression of receptor activator of NF-κB ligand (RANKL). We investigated the role of the calcineurin/nuclear factor of activated T-cells (NFAT) signaling pathway in TNFα-induced RANKL expression in C2C12 and primary cultured mouse calvarial cells. TNFα-induced RANKL expression was blocked by the calcineurin/NFAT pathway inhibitors. TNFα increased NFAT transcriptional activity and subsequent RANKL promoter binding. Mutations in the NFAT-binding element (MT(N)) suppressed TNFα-induced RANKL promoter activity. TNFα increased prostaglandin E2 (PGE₂) production, which in turn enhanced NFAT transcriptional activity and binding to the RANKL promoter. MT(N) suppressed PGE₂-induced RANKL promoter activity. TNFα and PGE₂ increased the expression of RANKL, NFAT cytoplasmic-1 (NFATc1), cAMP response element-binding protein (CREB), and cyclooxygenase 2 (COX2); which increment was suppressed by indomethacin, a COX inhibitor. Mutations in the CRE-like element blocked PGE₂-induced RANKL promoter activity. PGE₂ induced the binding of CREB to the RANKL promoter, whereas TNFα increased the binding of both CREB and NFATc1 to this promoter through a process blocked by indomethacin. The PGE₂ receptor antagonists AH6809 and AH23848 blocked TNFα-induced expression of RANKL, NFATc1, and CREB; transcriptional activity of NFAT; and binding of NFATc1 or CREB to the RANKL promoter. These results suggest that TNFα-induced RANKL expression depends on PGE₂ production and subsequent transcriptional activation/enhanced binding of NFATc1 and CREB to the RANKL promoter.

Teriparatide and denosumab combination therapy and skeletal metabolism

Several therapies are available for osteoporis. Understanding the bone turnover changes and their mutual realtionship gives an overall view and might lead to a target therapy INTRODUCTION: The aim of this study is to compare the changes in bone turnover markers in patients treated with either denosumab alone, teriparatide (TPTD) alone, or in a third therapeutic scheme, when TPTD was added to patients previously treated with denosumab.

METHODS

Fifty-nine women over 65 years old with severe postmenopausal osteoporosis (evidence of at least two moderate-severe vertebral fractures) were enrolled in the study. Serum samples were collected every 3 months. They were assayed for intact N-propeptide of type I collagen (P1NP), C-terminal telopeptide of type I collagen (CTX), intact parathyroid hormone (PTH), 25 hydroxy-vitamin D (25 OHD), Sclerostin (SOST), and Dickkopf-related protein 1 (DKK1). Bone mass density was assessed by dual-energy X-ray absorptiometry at the lumbar spine and at the total hip.

RESULTS

In the groups treated only with TPTD or with denosumab, bone turnover markers increased and decreased, respectively. In TPTD group, a later significant increase in DKK1 was observed, while in denosumab group, a progressive increase in SOST was associated with a progressive significant decrease in DKK1. In the group treated first with denosumab and in which TPTD was added 3 months later, both CTX and P1NP increased 3 months after the beginning of TPTD. The strong effect of denosumab on bone turnover seems to be reversed by TPTD treatment.

CONCLUSIONS

In this study, we showed that TPTD is able to express its biological activity even when bone turnover is fully suppressed by denosumab treatment. The combination therapy is associated with significant increases in both DKK1 and SOST.

Sclerostin expression in the subchondral bone of patients with knee osteoarthritis

The aim of this study was to assess the expression of β-catenin, transcription factor-4 (TCF-4) and sclerostin in the subchondral bone of patients with primary knee osteoarthritis (OA). Tibial plateau specimens from patients with OA who underwent total knee arthroplasty were classified into the early stage (n=15), intermediate stage (n=13) and late stage (n=17) groups using the Mankin score. Structural parameters, including total articular cartilage (TAC), subchondral bone plate (SCP) thickness and trabecular bone volume (BV/TV), were assessed using Image-Pro Plus 6.0 analysis software. Subsequently, β-catenin and sclerostin expression levels in subchondral bone were determined by immunohistochemistry. In addition, the mRNA and protein levels of β-catenin, TCF-4 and sclerostin were evaluated by RT-qPCR and western blot analysis, respectively. As regards the cartilage and subchondral bone structural parameters, TAC was reduced, while SCP thickness and BV/TV were increased due to OA, with significant differences observed among the different stages (all P<0.05). The results of immunohistochemistry revealed that the β-catenin levels in the intermediate- and late-stage samples were significantly increased, while the levels of sclerostin were markedly decreased compared with the values in the early-stage samples (all P<0.05). Compared with the intermediate-stage samples, the sclerostin levels were decreased, and SCP thickness and the β-catenin levels were increased in the late-stage samples (all P<0.05). The results of RT-qPCR and western blot analysis revealed that the β-catenin and TCF-4 mRNA and protein levels in the intermediate- and late-stage samples were significantly increased, while sclerostin expression was significantly decreased compared with the early-stage samples; a similar trend was observed between the intermediate- and late-stage samples (all P<0.05). Finally, the β-catenin and TCF-4 levels positively correlated with the Mankin scores, while there was a negative correlation with sclerostin expression. Our findings demonstrate that sclerostin expression is closely associated with the degree of joint damage in patients with OA, confirming its involvement in the development of OA.

β-catenin activity in late hypertrophic chondrocytes locally orchestrates osteoblastogenesis and osteoclastogenesis

Trabecular bone formation is the last step in endochondral ossification. This remodeling process of cartilage into bone involves blood vessel invasion and removal of hypertrophic chondrocytes (HTCs) by chondroclasts and osteoclasts. Periosteal- and chondrocyte-derived osteoprogenitors utilize the leftover mineralized HTC matrix as a scaffold for primary spongiosa formation. Here, we show genetically that β-catenin (encoded by Ctnnb1), a key component of the canonical Wnt pathway, orchestrates this remodeling process at multiple levels. Conditional inactivation or stabilization of β-catenin in HTCs by a Col10a1-Cre line locally modulated osteoclastogenesis by altering the Rankl:Opg ratio in HTCs. Lack of β-catenin resulted in a severe decrease of trabecular bone in the embryonic long bones. Gain of β-catenin activity interfered with removal of late HTCs and bone marrow formation, leading to a continuous mineralized hypertrophic core in the embryo and resulting in an osteopetrotic-like phenotype in adult mice. Furthermore, β-catenin activity in late HTCs is required for chondrocyte-derived osteoblastogenesis at the chondro-osseous junction. The latter contributes to the severe trabecular bone phenotype in mutants lacking β-catenin activity in HTCs.

Summary: The conditional modulation of β-catenin activity in late hypertrophic chondrocytes locally regulates osteoclast differentiation and the transdifferentiation of chondrocytes into osteoblasts.

Influence of single and binary doping of strontium and lithium on in vivo biological properties of bioactive glass scaffolds

Effects of strontium and lithium ion doping on the biological properties of bioactive glass (BAG) porous scaffolds have been checked in vitro and in vivo. BAG scaffolds were prepared by conventional glass melting route and subsequently, scaffolds were produced by evaporation of fugitive pore formers. After thorough physico-chemical and in vitro cell characterization, scaffolds were used for pre-clinical study. Soft and hard tissue formation in a rabbit femoral defect model after 2 and 4 months, were assessed using different tools. Histological observations showed excellent osseous tissue formation in Sr and Li + Sr scaffolds and moderate bone regeneration in Li scaffolds. Fluorochrome labeling studies showed wide regions of new bone formation in Sr and Li + Sr doped samples as compared to Li doped samples. SEM revealed abundant collagenous network and minimal or no interfacial gap between bone and implant in Sr and Li + Sr doped samples compared to Li doped samples. Micro CT of Li + Sr samples showed highest degree of peripheral cancellous tissue formation on periphery and cortical tissues inside implanted samples and vascularity among four compositions. Our findings suggest that addition of Sr and/or Li alters physico-chemical properties of BAG and promotes early stage in vivo osseointegration and bone remodeling that may offer new insight in bone tissue engineering.

Effect of the Chronic Use of Lithium Carbonate on Induced Tooth Movement in Wistar Rats

Patients who seek dental treatment may have bipolar disorder, and lithium carbonate (LC) is the drug of choice used in the treatment of this disorder. Taking into consideration the controversial results found in the literature, and the possible influence of LC on induced tooth movement, the objective was to evaluate tooth movement induced in rats after administration of lithium carbonate. One hundred and ninety-two rats were divided into 3 groups. In the L group, the animals received daily 60mg/kg of LC, they were not subjected to orthodontic movement, and they were euthanized after 33, 37, 44 or 51 days. In the LM group, the LC was administered for 30 days and during the subsequent 3, 7, 14 and 21 days, corresponding to the period of induced tooth movement, and they received a spring that produced a 30cN force. In the SM group, saline solution was applied. Measurements were made of tooth displacement, the numbers of osteoclasts and serum lithium phosphate (PO4), alkaline phosphatase (ALP) and creatinine levels. The tooth displacement was lower in the LM group compared to the SM group at 44 days. A tendency toward reduction in the number of osteoclasts was observed in the LM group compared to the SM group at 44 days. The average lithium were higher in the L and LM groups compared to the SM group. The opposite was observed for the PO4 group. A higher value for the ALP was found in the L group. The average creatinine level was lower in the LM group. LC inhibited tooth movement for 14 days, possibly due to the reduction in the number of osteoclasts.

Animal Models of Bone Loss in Inflammatory Arthritis: from Cytokines in the Bench to Novel Treatments for Bone Loss in the Bedside-a Comprehensive Review

Throughout life, bone is continuously remodelled. Bone is formed by osteoblasts, from mesenchymal origin, while osteoclasts induce bone resorption. This process is tightly regulated. During inflammation, several growth factors and cytokines are increased inducing osteoclast differentiation and activation, and chronic inflammation is a condition that initiates systemic bone loss. Rheumatoid arthritis (RA) is a chronic inflammatory auto-immune disease that is characterised by active synovitis and is associated with early peri-articular bone loss. Peri-articular bone loss precedes focal bone erosions, which may progress to bone destruction and disability. The incidence of generalised osteoporosis is associated with the severity of arthritis in RA and increased osteoporotic vertebral and hip fracture risk. In this review, we will give an overview of different animal models of inflammatory arthritis related to RA with focus on bone erosion and involvement of pro-inflammatory cytokines. In addition, a humanised endochondral ossification model will be discussed, which can be used in a translational approach to answer osteoimmunological questions.

P2X7 nucleotide receptor signaling potentiates the Wnt/β-catenin pathway in cells of the osteoblast lineage

The P2X7 and Wnt/β-catenin signaling pathways regulate osteoblast differentiation and are critical for the anabolic responses of bone to mechanical loading. However, whether these pathways interact to control osteoblast activity is unknown. The purpose of this study was to investigate the effects of P2X7 activation on Wnt/β-catenin signaling in osteoblasts. Using MC3T3-E1 cells, we found that combined treatment with Wnt3a and the P2X7 agonist 2'(3')-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP) elicited more sustained β-catenin nuclear localization than that induced by Wnt3a alone. Wnt3a-induced increases in β-catenin transcriptional activity were also potentiated by treatment with BzATP. Consistent with involvement of P2X7, a high ATP concentration (1 mM) potentiated Wnt3a-induced β-catenin transcriptional activity, whereas a low concentration (10 μM) of ATP, adenosine 5'-diphosphate (ADP), or uridine 5'-triphosphate (UTP) failed to elicit a response. The potentiation of β-catenin transcriptional activity elicited by BzATP was also inhibited by two distinct P2X7 antagonists: A 438079 and A 740003. Furthermore, responses to Wnt3a in calvarial cells isolated from P2rx7 knockout mice were significantly less than in cells from wild-type controls. In MC3T3-E1 cells, BzATP increased inhibitory phosphorylation of glycogen synthase kinase 3β (GSK3β), a process that was blocked by A 438079 and diminished by inhibition of protein kinase C. Thus, P2X7 signaling may potentiate the canonical Wnt pathway through GSK3β inhibition. Taken together, we show that P2X7 activation prolongs and potentiates Wnt/β-catenin signaling. Consequently, cross-talk between P2X7 and Wnt/β-catenin pathways may modulate osteoblast activity in response to mechanical loading.

Epithelium-Derived Wnt Ligands Are Essential for Maintenance of Underlying Digit Bone

Clinically, many nail disorders accompany bone deformities, but whether the two defects are causally related is under debate. To investigate the potential interactions between the two tissue types, we analyzed epithelial-specific β-catenin-deficient mice, in which nail differentiation is abrogated. These mice showed regression of not only the nail plate but also of the underlying digit bone. Characterization of these bone defects revealed active bone resorption, which is suppressed by Wnt activation in osteoblast and osteoclast precursors. Furthermore, we found that Wntless expression, essential for Wnt ligand secretion, was lacking in the β-catenin-deficient nail epithelium and that genetic deletion of Wntless (Wls) in the nail epithelium led to the lack of Wnt activation in osteoblast and osteoclast precursors and subsequently led to defective regression of the underlying digit bone. Together, these data show that epithelial Wnt ligands can ultimately regulate Wnt signaling in osteoblast and osteoclast precursors, known to regulate bone homeostasis. These results reveal a critical role for the nail epithelium on the digit bone during homeostatic regeneration and show that Wnt/β-catenin signaling is critical for this interaction.

Tumor necrosis factor alpha suppresses osteogenic differentiation of MSCs by inhibiting semaphorin 3B via Wnt/β-catenin signaling in estrogen-deficiency induced osteoporosis

The proinflammatory cytokines, especially tumor necrosis factor alpha (TNF-α), have been shown to inhibit osteogenic differentiation of mesenchymal stem cells (MSCs) and bone formation in estrogen-deficiency-induced osteoporosis, but the mechanisms of TNF-α impaired bone formation remain poorly understood. Semaphorins have been shown to regulate cell growth, cell migration, and cell differentiation in a variety of tissues, including bone tissue. Here, we identified a novel mechanism whereby TNF-α, suppressing Semaphorin3B expression contributes to estrogen-deficiency-induced osteoporosis. In this study, we found that TNF-α could decrease Semaphorin3B expression in osteogenic differentiation of MSCs. Overexpression of Semaphorin3B in MSCs attenuated the inhibitory effects of TNF-α on MSCs proliferation and osteoblastic differentiation. Mechanistically, activation of the Wnt/β-catenin signaling markedly rescued TNF-α-inhibited Semaphorin3B expression, suggesting that Wnt/β-catenin signaling was involved in the regulation of Semaphorin3B expression by TNF-α. Taken together, our results revealed a novel function for Semaphorin3B and suggested that suppressed Semaphorin3B may contribute to impaired bone formation by elevated TNF-α in estrogen-deficiency-induced osteoporosis. This study may indicate a therapeutic target gene of Semaphorin3B for osteoporosis.

Effect of Pulsed Electromagnetic Field on Bone Formation and Lipid Metabolism of Glucocorticoid-Induced Osteoporosis Rats through Canonical Wnt Signaling Pathway

Pulsed electromagnetic field (PEMF) has been suggested as a promising method alternative to drug-based therapies for treating osteoporosis (OP), but the role of PEMF in GIOP animal models still remains unknown. This study was performed to investigate the effect of PEMF on bone formation and lipid metabolism and further explored the several important components and targets of canonical Wnt signaling pathway in GIOP rats. After 12 weeks of intervention, bone mineral density (BMD) level of the whole body increased significantly, serum lipid levels decreased significantly, and trabeculae were thicker in GIOP rats of PEMF group. PEMF stimulation upregulated the mRNA and protein expression of Wnt10b, LRP5, β-catenin, OPG, and Runx2 and downregulated Axin2, PPAR-γ, C/EBPα, FABP4, and Dkk-1. The results of this study suggested that PEMF stimulation can prevent bone loss and improve lipid metabolism disorders in GIOP rats. Canonical Wnt signaling pathway plays an important role in bone formation and lipid metabolism during PEMF stimulation.