Wnt signalling pathway: a new target for the treatment of osteoporosis

Multifunctional scaffolds for bone repair following age-related biological decline: Promising prospects for smart biomaterial-driven technologies

The repair of large bone defects due to trauma, disease, and infection can be exceptionally challenging in the elderly. Despite best clinical practice, bone regeneration within contemporary, surgically implanted synthetic scaffolds is often problematic, inconsistent, and insufficient where additional osteobiological support is required to restore bone. Emergent smart multifunctional biomaterials may drive important and dynamic cellular crosstalk that directly targets, signals, stimulates, and promotes an innate bone repair response following age-related biological decline and when in the presence of disease or infection. However, their role remains largely undetermined. By highlighting their mechanism/s and mode/s of action, this review spotlights smart technologies that favorably align in their conceivable ability to directly target and enhance bone repair and thus are highly promising for future discovery for use in the elderly. The four degrees of interactive scaffold smartness are presented, with a focus on bioactive, bioresponsive, and the yet-to-be-developed autonomous scaffold activity. Further, cell- and biomolecular-assisted approaches were excluded, allowing for contemporary examination of the capabilities, demands, vision, and future requisites of next-generation biomaterial-induced technologies only. Data strongly supports that smart scaffolds hold significant promise in the promotion of bone repair in patients with a reduced osteobiological response. Importantly, many techniques have yet to be tested in preclinical models of aging. Thus, greater clarity on their proficiency to counteract the many unresolved challenges within the scope of aging bone is highly warranted and is arguably the next frontier in the field. This review demonstrates that the use of multifunctional smart synthetic scaffolds with an engineered strategy to circumvent the biological insufficiencies associated with aging bone is a viable route for achieving next-generation therapeutic success in the elderly population.

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.

Comparative Study of the Cytokine Profiles of Serum and Tissues from Patients with the Ossification of the Posterior Longitudinal Ligament

BACKGROUND

The ossification of the posterior longitudinal ligament (OPLL) is one of the contributing factors leading to severe cervical spondylotic myelopathy (CSM). The mechanism causing ossification is still unclear. The current study was designed to analyze the specimens of patients with or without OPLL.

METHODS

The study collected 51 patients with cervical spondylosis. There were six serum samples in both the non-OPLL (NOPLL) and OPLL groups. For tissue analysis, there were seven samples in the NOPLL group and five samples in the OPLL group. The specimens of serum and tissue were analyzed by using Human Cytokine Antibody Arrays to differentiate biomarkers between the OPLL and NOPLL groups, as well as between serum and OPLL tissue. Immunohistochemical staining of the ligament tissue was undertaken for both groups.

RESULTS

For OPLL vs. NOPLL, the serum leptin levels are higher in the OPLL group, corroborating others' observations that it may serve as a disease marker. In the tissue, angiogenin (ANG), osteopontin (OPN), and osteopro-tegerin (OPG) are higher than they are in the OPLL group (p < 0.05). For serum vs. OPLL tissue, many chemotactic cytokines demonstrated elevated levels of MIP1 delta, MCP-1, and RANTES in the serum, while many cytokines promoting or regulating bone genesis were up-regulated in tissue (oncostatin M, FGF-9, LIF, osteopontin, osteoprotegerin, TGF-beta2), as well as the factor that inhibits osteoclastogenesis (IL-10), with very few cytokines responsible for osteoclastogenesis. Molecules promoting angiogenesis, including angiotensin, vEGF, and osteoprotegerin, are abundant in the OPLL tissue, which paves the way for robust bone growth.

The fatty acid synthase inhibitor C75 differentially affects the adipogenic differentiation of multipotent cells and preadipocytes

Previously, we revealed the dual enhancing effect of netoglitazone, an agonist of the peroxisome proliferator-activated receptor γ, on adipogenesis and osteoblastogenesis, and reported that fatty acid synthase (FASN) knockdown selectively repressed its pro-adipogenic effect. Here, we examined if a FASN inhibitor, C75, could selectively repress the pro-adipogenic effect of netoglitazone. Surprisingly, C75 promoted the adipogenic differentiation of multipotent C3H10T1/2 cells but inhibited 3T3-L1 preadipocytes. By identifying glycogen synthase kinase-3β and intracellular cAMP levels as regulatory targets of C75, we ultimately found the differential expression of adenosine receptor 3 (AR3) and AR2a on these cells. Inhibition of AR3 on C3H10T1/2 and AR2a on 3T3-L1 inhibited the effects of C75 on the differentiation of these cells. Our findings imply that cell-type-specific AR expression might account for the differential adipogenic effects of C75.

Progress of Signaling Pathways, Stress Pathways and Epigenetics in the Pathogenesis of Skeletal Fluorosis

Fluorine is widely dispersed in nature and has multiple physiological functions. Although it is usually regarded as an essential trace element for humans, this view is not held universally. Moreover, chronic fluorosis, mainly characterized by skeletal fluorosis, can be induced by long-term excessive fluoride consumption. High concentrations of fluoride in the environment and drinking water are major causes, and patients with skeletal fluorosis mainly present with symptoms of osteosclerosis, osteochondrosis, osteoporosis, and degenerative changes in joint cartilage. Etiologies for skeletal fluorosis have been established, but the specific pathogenesis is inconclusive. Currently, active osteogenesis and accelerated bone turnover are considered critical processes in the progression of skeletal fluorosis. In recent years, researchers have conducted extensive studies in fields of signaling pathways (Wnt/β-catenin, Notch, PI3K/Akt/mTOR, Hedgehog, parathyroid hormone, and insulin signaling pathways), stress pathways (oxidative stress and endoplasmic reticulum stress pathways), epigenetics (DNA methylation and non-coding RNAs), and their inter-regulation involved in the pathogenesis of skeletal fluorosis. In this review, we summarised and analyzed relevant findings to provide a basis for comprehensive understandings of the pathogenesis of skeletal fluorosis and hopefully propose more effective prevention and therapeutic strategies.

Experimental agents to improve fracture healing: utilizing the WNT signaling pathway

The process of bone healing largely recapitulates bone development in the embryo and ideally achieves complete restoration of bone shape and structure. However, because successful fracture healing requires tight interactions of numerous cell types and signaling molecules, any disruption of this highly coordinated processes can result in delayed healing or even non-union formation. The rate of fracture healing complications in orthopedic patients is reported to be 5-20%. Therefore, there is a need for new therapeutic strategies to improve fracture healing in patients with healing complications. One treatment strategy would include the easy and safe application of a pharmacological agent inducing osteoanabolic effects during fracture healing. One potential promising molecular target is the osteoanabolic WNT signaling pathway. This pathway plays an important role during embryonic bone development, homeostasis, mechanotransduction, development of osteoporosis and bone regeneration. This review focuses on preclinical studies targeting WNT signaling molecules to accelerate fracture healing. The three main investigated antagonists of the WNT signaling pathway, which can be blocked experimentally by antibodies, are Sclerostin, Dickkopf-1 and Midkine. Treating animals with antibodies against these proteins enhanced bone formation in the fracture callus. This indicates a therapeutic potential for these antibodies to accelerate fracture healing in patients with orthopedic complications.

Role of the RANK/RANKL/OPG and Wnt/β-Catenin Systems in CKD Bone and Cardiovascular Disorders

In the course of chronic kidney disease (CKD), alterations in the bone-vascular axis augment the risk of bone loss, fractures, vascular and soft tissue calcification, left ventricular hypertrophy, renal and myocardial fibrosis, which markedly increase morbidity and mortality rates. A major challenge to improve skeletal and cardiovascular outcomes in CKD patients requires a better understanding of the increasing complex interactions among the main modulators of the bone-vascular axis. Serum parathyroid hormone (PTH), phosphorus (P), calcium (Ca), fibroblast growth factor 23 (FGF23), calcidiol, calcitriol and Klotho are involved in this axis interact with RANK/RANKL/OPG system and the Wnt/β-catenin pathway. The RANK/RANKL/OPG system controls bone remodeling by inducing osteoblast synthesis of RANKL and downregulating OPG production and it is also implicated in vascular calcification. The complexity of this system has recently increased due the discovery of LGR4, a novel RANKL receptor involved in bone formation, but possibly also in vascular calcification. The Wnt/β-catenin pathway plays a key role in bone formation: when this pathway is activated, bone is formed, but when it is inhibited, bone formation is stopped. In the progression of CKD, a downregulation of the Wnt/β-catenin pathway has been described which occurs mainly through the not coincident elevations of sclerostin, Dickkopf1 (Dkk1) and the secreted Frizzled Related Proteins (sFRPs). This review analyzes the interactions of PTH, P, Ca, FGF23, calcidiol, calcitriol and Klotho with the RANKL/RANKL/OPG system and the Wnt/β-catenin, pathway and their implications in bone and cardiovascular disorders in CKD.

Osteoblast-n-Osteoclast: Making Headway to Osteoporosis Treatment

Background:

Bone is a dynamic tissue that continuously undergoes the modeling and remodeling process to maintain its strength and firmness. Bone remodeling is determined by the functioning of osteoblast and osteoclast cells. The imbalance between the functioning of osteoclast and osteoblast cells leads to osteoporosis. Osteoporosis is divided into primary and secondary osteoporosis. Generally, osteoporosis is diagnosed by measuring bone mineral density (BMD) and various osteoblast and osteoclast cell markers.

Methods:

Relevant literature reports have been studied and data has been collected using various search engines like google scholar, scihub, sciencedirect, pubmed, etc. A thorough understanding of the mechanism of bone targeting strategies has been discussed and related literature has been studied and compiled.

Results:

Bone remodeling process has been described in detail including various approaches for targeting bone. Several bone targeting moieties have been stated in detail along with their mechanisms. Targeting of osteoclasts and osteoblasts using various nanocarriers has been discussed in separate sections. The toxicity issues or Biosafety related to the use of nanomaterials have been covered.

Conclusion:

The treatment of osteoporosis targets the inhibition of bone resorption and the use of agents that promote bone mineralization to slow disease progression. Current osteoporosis therapy involves the use of targeting moieties such as bisphosphonates and tetracyclines for targeting various drugs. Nanotechnology has been used for targeting various drug molecules such as RANKLinhibitors, parathyroid hormone analogues, estrogen agonists and antagonists, Wnt signaling enhancer and calcitonin specifically to bone tissue (osteoclast and osteoblasts). So, a multicomponent treatment strategy targeting both the bone cells will be more effective rather than targeting only osteoclasts and it will be a potential area of research in bone targeting used to treat osteoporosis. The first section of the review article covers various aspects of bone targeting. Another section comprises details of various targeting moieties such as bisphosphonates, tetracyclines; and various nanocarriers developed to target osteoclast and osteoblast cells and summarized data on in vivo models has been used for assessment of bone targeting, drawbacks of current strategies and future perspectives.

Re-appraising the potential of naringin for natural, novel orthopedic biotherapies

Naringin is a naturally occurring flavonoid found in plants of the Citrus genus that has historically been used in traditional Chinese medical regimens for the treatment of osteoporosis. Naringin modulates signaling through numerous molecular pathways critical to musculoskeletal development, cellular differentiation, and inflammation. Administration of naringin increases in vitro expression of bone morphogenetic proteins (BMPs) and activation of the Wnt/β-catenin and extracellular signal-related kinase (Erk) pathways, thereby promoting osteoblastic proliferation and differentiation from stem cell precursors for bone formation. Naringin also inhibits osteoclastogenesis by both modifying RANK/RANKL interactions and inducing apoptosis in osteoclasts in vitro. In addition, naringin acts on the estrogen receptor in bone to mimic the native bone-preserving effects of estrogen, with few systemic side effects on other estrogen-sensitive tissues. The efficacy of naringin therapy in reducing the osteolysis characteristic of common musculoskeletal pathologies such as osteoporosis, degenerative joint disease, and osteomyelitis, as well as inflammatory conditions affecting bone such as diabetes mellitus, has been extensively demonstrated in vitro and in animal models. Naringin thus represents a naturally abundant, cost-efficient agent whose potential for use in novel musculoskeletal biotherapies warrants re-visiting and further exploration through human studies. Here, we review the cellular mechanisms of action that have been elucidated regarding the action of naringin on bone resident cells and the bone microenvironment, in vivo evidence of naringin’s osteostimulative and chondroprotective properties in the setting of osteolytic bone disease, and current limitations in the development of naringin-containing translational therapies for common musculoskeletal conditions.

Exploring the Mechanism of Icariin in Osteoporosis Based on a Network Pharmacology Strategy

BACKGROUND With the aging of the world's population, the incidence of osteoporosis (OP) has become a public health problem of worldwide concern. Research shows that icariin may have a therapeutic effect on OP. MATERIAL AND METHODS PharmMapper was utilized to predict the potential targets of icariin. GeneCards and Online Mendelian Inheritance in Man (OMIM) were used for the collection of OP genes. The STRING database was utilized to obtain the protein-protein interaction (PPI) data. We used Cytoscape 3.7.2 to construct and analyze the networks. The genes and targets in the networks were input into the Database for Annotation, Visualization and Integrated Discovery (DAVID) to undergo Gene Ontology (GO) and pathway enrichment analysis. Finally, animal experiments were performed to verify the prediction results of this study. RESULTS A total of 297 icariin potential targets and 262 OP genes were obtained, and an icariin-OP PPI network was constructed and analyzed. The results of the GO enrichment analysis showed that icariin can regulate the steroid hormone-mediated signaling pathway, skeletal system development, extracellular space, cytosol, and steroid hormone receptor activity. The results of the pathway enrichment analysis showed that icariin can regulate osteoclast differentiation, FoxO, estrogen, and PPAR signaling pathways. The results of the experiments showed that icariin can increase estradiol, ß-catenin, and Receptor Activator of Nuclear Factor-к B Ligand (RANKL)/osteoprotegerin (OPG) ratio in postmenopausal OP rats (P<0.05). CONCLUSIONS This research found that the icariin can regulate OP-related biological processes, cell components, molecular functions, and signaling pathways.

Novel insights into the complex architecture of osteoporosis molecular genetics

Osteoporosis is a prevalent osteodegenerative disease and silent killer linked to a decrease in bone mass and decline of bone microarchitecture, due to impaired bone matrix mineralization, raising the risk of fracture. Nevertheless, the process of bone matrix mineralization is still an unsolved mystery. Osteoporosis is a polygenic disorder associated with genetic and environmental risk factors; however, the majority of genes associated with osteoporosis remain largely unknown. Several signaling pathways regulate bone mass; therefore, dysregulation of a single signaling pathway leads to metabolic bone disease owing to high or low bone mass. Parathyroid hormone, core-binding factor α-1 (Cbfa1), Wnt/β-catenin, the receptor activator of the nuclear factor kappa-B (NF-κB) ligand (RANKL), myostatin, and osteogenic exercise signaling pathways play pivotal roles in the regulation of bone mass. The myostatin signaling pathway increases bone resorption by activating the RANKL signaling pathway, whereas osteogenic exercise inhibits myostatin and sclerostin while inducing irisin that consequentially activates the Cbfa1 and Wnt/β-catenin bone formation pathways. The aims of this review are to summarize what is known about osteoporosis-related signaling pathways; define the role of these pathways in osteoporosis drug discovery; focus light on the link between bone, muscle, pancreas, and adipose integrative physiology and osteoporosis; and underline the emerging role of osteogenic exercise in the prevention of, and care for, osteoporosis, obesity, and diabetes.

An update on therapies for the treatment of diabetes-induced osteoporosis

Introduction: Currently, 424 million people aged between 20 and 79 years worldwide are diabetic. More than 25% of adults aged over 65 years in North America have Type 2 diabetes mellitus (DM). Diabetes-induced osteoporosis (DM-OS) is caused by chronic hyperglycemia, advanced glycated end products and oxidative stress. The increase in the prevalence of DM-OS has prompted researchers to develop new biological therapies for the management of DM-OS. Areas covered: This review covered the current and novel biological agents used in the management of DM-OS. Data were retrieved from PubMed, Scopus, American Diabetes Association and International Osteoporosis Foundation websites, and ClinicalTrials.gov. The keywords for the search included: DM, osteoporosis, and management. Expert opinion: Several biological molecules have been examined in order to find efficient drugs for the treatment of DM-OS. These biological agents include anti-osteoporosis drugs: net anabolics (parathyroid hormone/analogs, androgens, calcilytics, anti-sclerostin antibody), net anti-resorptive osteoporosis drugs (calcitonin, estrogen, selective estrogen receptor modulators, bisphosphonates, RANKL antibody) and anti-diabetic drugs (alpha glucosidase inhibitors, sulfonylureas, biguanides, meglitinides, thiazolidinediones, GLP-1 receptor agonists, dipeptidylpeptidase-4 inhibitors, sodium glucose co-transporter-2 inhibitors, insulin). Biological medications that effectively decrease hyperglycemia and, at the same time, maintain bone health would be an ideal drug/drug combination for the treatment of DM-OS.

Cooperative impact of thiazolidinedione and fatty acid synthase on human osteogenesis

Previous, we found that the small molecules capable of inhibiting the expression and the pro-adipogenic activity of ZNF521 might improve the osteogenic performance of aging human bone marrow MSCs (bmMSCs), and that fatty acid synthase (FASN) was a critical effector of ZNF521's pro-adipogenic activity. Here, by characterizing the netoglitazone (MCC-555), one of the thiazolidinediones known as adipogenic enhancers, as an inhibitor of ZNF521 expression, we found that MCC-555 indeed also harbored pro-osteoblastic effect. Investigation revealed that MCC-555 might function as a GSK3β inhibitor to promote osteoblastogenesis and bone formation. Importantly, combination of MCC-555 with FASN knockdown, but not with GW9662 (a PPARγ2 antagonist), blocked the pro-adipogenic but retained the pro-osteoblastic effect of MCC-555. Using a 3-dimentional culture system, we showed that MCC-555 facilitated the FASN-knockdown of aging human bmMSCs to form cell clusters in scaffolds, and to promote osteoblastic differentiation and biomineralization in cell clusters. These data indicated that MCC-555 promoted bmMSCs to produce bone-like tissues. Our data narrate a thiazolidinedione-based novel strategy to improve the osteogenic performance of aging bmMSCs to support the application of autologous aging bmMSCs in cell therapy and in producing bone-like tissues for repairing bone injury in the elderly.

(R)‑dehydroxyabscisic alcohol β‑D‑apiofuranosyl‑(1ˮ→6')‑β‑D‑glucopyranoside enhances the osteoblastic differentiation of ST2 cells via the BMP/WNT pathways

Lonicera japonica has been used in traditional Chinese medicine as an important medicinal plant, with the ability to inhibit osteoclast development and bone loss. However, it is not clear which active ingredient exerts these effects. (R)-dehydroxyabscisic alcohol β-D-apiofuranosy l-(1ˮ→6’)-β-D-glucopyranoside (DAG) is an active constituent isolated from Lonicera japonica. In the present study, the ST2 bone marrow stromal cell line was treated by DAG at different concentrations and the osteoblastic differentiation was explored by ELISA assay, Von Kossa staining, Alizarin Red S staining, reverse transcription-quantitative polymerase chain reaction and western blot analysis. The results revealed that DAG promoted osteoblastic differentiation, as evidenced by increasing mineralization and alkaline phosphatase (ALP) activity, as well as the expression of genes encoding bone differentiation markers, including Alp, osteopontin (Opn) and osteocalcin (Ocn). In addition, DAG upregulated the gene expression of bone morphogenetic protein (Bmp)-2, Bmp4, Wnt family member (Wnt)-1, Wnt3 and runt-related transcription factor 2 (Runx2), as well as the protein expression of phosphorylated-mothers against decapentaplegic homolog (Smad) 1, Smad5 Smad8, β-catenin and Runx2 in ST2 cells. The osteogenic effects induced by DAG were attenuated by the BMP antagonist Noggin and the WNT signaling pathway inhibitor Dickkopf related protein-1. The data indicated that DAG promoted the osteoblastic differentiation of ST2 cells, at least partially through regulating the BMP/WNT signaling pathways. This provides scientific rationale for the development of DAG as a treatment for bone loss-associated diseases, such as osteoporosis.

V-ATPases and osteoclasts: ambiguous future of V-ATPases inhibitors in osteoporosis

Vacuolar ATPases (V-ATPases) play a critical role in regulating extracellular acidification of osteoclasts and bone resorption. The deficiencies of subunit a3 and d2 of V-ATPases result in increased bone density in humans and mice. One of the traditional drug design strategies in treating osteoporosis is the use of subunit a3 inhibitor. Recent findings connect subunits H and G1 with decreased bone density. Given the controversial effects of ATPase subunits on bone density, there is a critical need to review the subunits of V-ATPase in osteoclasts and their functions in regulating osteoclasts and bone remodeling. In this review, we comprehensively address the following areas: information about all V-ATPase subunits and their isoforms; summary of V-ATPase subunits associated with human genetic diseases; V-ATPase subunits and osteopetrosis/osteoporosis; screening of all V-ATPase subunits variants in GEFOS data and in-house data; spectrum of V-ATPase subunits during osteoclastogenesis; direct and indirect roles of subunits of V-ATPases in osteoclasts; V-ATPase-associated signaling pathways in osteoclasts; interactions among V-ATPase subunits in osteoclasts; osteoclast-specific V-ATPase inhibitors; perspective of future inhibitors or activators targeting V-ATPase subunits in the treatment of osteoporosis.

Inhibition of osteogenesis surrounding the titanium implant by CGRP deficiency

Previous studies have suggested one of the neurotransmitters, calcitonin gene-related peptide (CGRP), modulates local regulation of bone metabolism; however, the regulating signaling pathway is still being explored. The objective of this study was to determine whether CGRP deficiency affects the osteogenesis surrounding titanium implants in vivo. Titanium screws were implanted in 72 adult rats, which were divided into three groups randomly: Sham, inferior alveolar neurectomy (IAN), and IAN+CGRP. Saline solution containing CGRP (concentration: 100 nmol/L) was injected into the area surrounding the implants in the IAN+CGRP group every day post operation. According to histological observations and Micro-CT, osteogenesis surrounding the implant was suppressed in the IAN group compared to that in the Sham and IAN+CGRP groups; the highest degree of osteogenesis was observed in the Sham group. This effect was also proved via the gene expressions of osteocalcin and runt-related transcription factor 2 surrounding the implant by real-time (RT) PCR analysis. In addition, through immunofluorescence staining and RT-PCR analysis, levels of CGRP and β-catenin were also reduced in the IAN group, while the highest expression was observed in the Sham group (p < 0.05). Our results collectively suggest that the titanium implant bone model established by IAN exhibited CGRP deficiency and reduced osteogenesis surrounding the implant. Additionally, the expression analyses suggest that the canonical Wnt signaling pathway could be involved in this process of bone metabolism in vivo.

Thermodynamics in cancers: opposing interactions between PPAR gamma and the canonical WNT/beta-catenin pathway

Cancer cells are the site of numerous metabolic and thermodynamic abnormalities. We focus this review on the interactions between the canonical WNT/beta-catenin pathway and peroxisome proliferator-activated receptor gamma (PPAR gamma) in cancers and their implications from an energetic and metabolic point of view. In numerous tissues, PPAR gamma activation induces inhibition of beta-catenin pathway, while the activation of the canonical WNT/beta-catenin pathway inactivates PPAR gamma. In most cancers but not all, PPAR gamma is downregulated while the WNT/beta-catenin pathway is upregulated. In cancer cells, upregulation of the WNT/beta-catenin signaling induces dramatic changes in key metabolic enzymes that modify their thermodynamic behavior. This leads to activation of pyruvate dehydrogenase kinase1 (PDK-1) and monocarboxylate lactate transporter. Consequently, phosphorylation of PDK-1 inhibits the pyruvate dehydrogenase complex (PDH). Thus, a large part of pyruvate cannot be converted into acetyl-coenzyme A (acetyl-CoA) in mitochondria and only a part of acetyl-CoA can enter the tricarboxylic acid cycle. This leads to aerobic glycolysis in spite of the availability of oxygen. This phenomenon is referred to as the Warburg effect. Cytoplasmic pyruvate is converted into lactate. The WNT/beta-catenin pathway induces the transcription of genes involved in cell proliferation, i.e., MYC and CYCLIN D1. This ultimately promotes the nucleotide, protein and lipid synthesis necessary for cell growth and multiplication. In cancer, activation of the PI3K-AKT pathway induces an increase of the aerobic glycolysis. Moreover, prostaglandin E2 by activating the canonical WNT pathway plays also a role in cancer. In addition in many cancer cells, PPAR gamma is downregulated. Moreover, PPAR gamma contributes to regulate some key circadian genes. In cancers, abnormalities in the regulation of circadian rhythms (CRs) are observed. CRs are dissipative structures which play a key-role in far-from-equilibrium thermodynamics. In cancers, metabolism, thermodynamics and CRs are intimately interrelated.

Neuropeptide Y enhances proliferation and prevents apoptosis in rat bone marrow stromal cells in association with activation of the Wnt/β-catenin pathway in vitro

Neuropeptide Y (NPY) exhibits a critical but poorly understood regulatory signaling function and has been shown to promote proliferation, vascularization and migration in several types of cells and tissues. However, little is known about the specific role of NPY in the proliferation and apoptosis of bone marrow stromal cells (also known as bone marrow-derived mesenchymal stem cells, BMSCs), which contain a subpopulation of multipotent skeletal stem cells. Based on BrdU incorporation tests, Cell Counting Kit-8, flow cytometry, quantitative polymerase chain reaction and western blotting, we showed that NPY significantly promoted the proliferation of BMSCs in a concentration-dependent manner, with a maximal effect observed at a concentration of 10^-10M for pro-proliferative and 10^-12M for anti-apoptotic activities. Furthermore, NPY significantly increased the percentage of cells in S and G2/M phases. In addition, NPY exhibited a protective effect after 24h of serum starvation as illustrated by a reduction in the apoptosis rate, degree of nuclear condensation, and expression of apoptosis markers, including caspase-3, caspase-9 and Bax mRNA expression. NPY also increased the mRNA and protein expression levels of canonical Wnt signaling pathway proteins, including β-catenin and c-myc, during the induced proliferative and anti-apoptotic processes. However, the proliferative and anti-apoptotic activities of NPY were partially blocked by both PD160170 (1μM) and DKK1 (0.2μg/mL). These compounds also blocked the mRNA and protein expression of β-catenin, p-GSK-3β and c-myc. Therefore, the results of the present study demonstrated that NPY exerts a proliferative and protective effect on BMSCs in a dose- and time-dependent manner in vitro, and importantly, these effects may be mediated via its Y1 receptor and involved in activation of the canonical Wnt signaling pathway.

Interleukin 6/Wnt interactions in rheumatoid arthritis: interleukin 6 inhibits Wnt signaling in synovial fibroblasts and osteoblasts

Aim

To evaluate the impact of previously unrecognized negative interaction between the Wnt and interleukin (IL) 6 signaling pathways in skeletal tissues as a possible major mechanism leading to age- and inflammation-related destruction of bone and joints.

Methods

Luciferase reporter assays were performed to monitor Wnt pathway activation upon IL-6 and tumor necrosis factor-α (TNFα) treatment. Functional contribution of IL-6 and TNFα interaction to inhibition of bone formation was evaluated in vitro using small hairpin RNAs (shRNA) in mouse mesenchymal precursor cells (MPC) of C2C12 and KS483 lines induced to differentiate into osteoblasts by bone morphogenetic proteins (BMP).

Results

IL-6 inhibited the activation of Wnt signaling in primary human synoviocytes, and, together with TNFα and Dickkopf-1, inhibited the activation of Wnt response. ShRNA-mediated knockdown of IL-6 mRNA significantly increased early BMP2/7-induced osteogenesis and rescued it from the negative effect of TNFα in C2C12 cells, as well as intensified bone matrix mineralization in KS483 cells.

Conclusion

IL-6 is an important mediator in the inhibition of osteoblast differentiation by TNFα, and knockdown of IL-6 partially rescues osteogenesis from the negative control of inflammation. The anti-osteoblastic effects of IL-6 are most likely mediated by its negative interaction with Wnt signaling pathway.

Correlation of blood bone turnover biomarkers and Wnt signaling antagonists with AS, DISH, OPLL, and OYL

Background

Wnt signaling plays an important role in development and maintenance of many organs and tissues. The most-studied secreted Wnt inhibitors are sclerostin (SOST), Dickkopf-related protein 1 (DKK-1), and secreted frizzled related protein 1 (SFRP-1) which play important roles in bone turnover. The present study investigated the relationship between serum Wnt inhibitors and diseases with excessive ossification structures, such as ossification of posterior longitudinal ligament (OPLL), ankylosing spondylitis (AS), diffuse idiopathic skeletal hyperostosis (DISH), and ossification of yellow ligament (OYL).

Methods

Twenty-five patients with AS, DISH, OPLL, or OYL were recruited in this study. Fasting peripheral blood samples were collected from all patients and nine controls. Various biomarkers of bone turnover including osteocalcin (OSC), osteoprotegerin (OPG), SFRP-1, DKK-1, and SOST were investigated.

Results

Our data showed that serum levels of OSC were higher, but Dkk-1 levels were lower in AS, DISH, OPLL, and OYL patients than those in the controls. Serum levels of SFRP-1 were significantly higher in DISH patients than those in the controls. Serum levels of SOST were significantly higher in DISH and OPLL patients than both levels in the controls. Serum levels of OPG were lower in AS patients than those in the controls. Serum levels of OSC were higher in the OPLL patients than those in the AS patients. Serum levels of DKK-1, SFRP-1, SOST, and OPG were not significantly different between the different disease groups.

Conclusions

In this exploratory study, both OSC and DKK-1 levels are correlated with the clinical conditions associated with excessive ossification, indicating that blood OSC and DKK-1 levels may serve as diagnostic biomarkers for AS, DISH, OPLL, and OYL. These findings may also help discover potential drug therapies for management of these diseases in the future.

Animal models for glucocorticoid-induced postmenopausal osteoporosis: An updated review

Glucocorticoid-induced postmenopausal osteoporosis is a severe osteoporosis, with high risk of major osteoporotic fractures. This severe osteoporosis urges more extensive and deeper basic study, in which suitable animal models are indispensable. However, no relevant review is available introducing this model systematically. Based on the recent studies on GI-PMOP, this brief review introduces the GI-PMOP animal model in terms of its establishment, evaluation of bone mass and discuss its molecular mechanism. Rat, rabbit and sheep with their respective merits were chosen. Both direct and indirect evaluation of bone mass help to understand the bone metabolism under different intervention. The crucial signaling pathways, miRNAs, osteogenic- or adipogenic- related factors and estrogen level may be the predominant contributors to the development of glucocorticoid-induced postmenopausal osteoporosis.

Polygonatum sibiricum polysaccharide inhibits osteoporosis by promoting osteoblast formation and blocking osteoclastogenesis through Wnt/β-catenin signalling pathway

Bone homeostasis is maintained by a balance between bone formation by osteoblasts and bone resorption by osteoclasts. Osteoporosis occurs when osteoclast activity surpasses osteoblast activity. Our previous studies showed the plant-derived natural polysaccharide (Polygonatum sibiricum polysaccharide or PSP) had significant anti-ovariectomy (OVX)-induced osteoporosis effects in vivo, but the mechanisms of PSP’s anti-osteoporosis effect remains unclear. In this study, we assessed PSP’s effect on the generation of osteoblast and osteoclast in vitro. This study showed that PSP promoted the osteogenic differentiation of mouse bone marrow stromal cells (BMSCs) without affecting BMPs signaling pathway. This effect was due to the increased nuclear accumulation of β-catenin, resulting in a higher expression of osteoblast-related genes. Furthermore, the study showed PSP could inhibit the receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis and exert prophylatic protection against LPS-induced osteolysis in vivo. This effect was also related to the increased nuclear accumulation of β-catenin, resulting in the decreased expression of osteoclast-related genes. In conclusion, our results showed that PSP effectively promoted the osteogenic differentiation of mouse BMSCs and suppressed osteoclastogenesis; therefore, it could be used to treat osteoporosis.

Plumbagin exhibits an anti-proliferative effect in human osteosarcoma cells by downregulating FHL2 and interfering with Wnt/β-catenin signalling

Plumbagin, a naphthoquinone constituent of Plumbago zeylanica L. (Plumbaginaceae) is widely used in traditional Chinese medicine as an antifungal, antibacterial and anti-inflammatory agent. Plumbagin is known to exhibit proapoptotic, antiangiogenic and antimetastatic effects in cancer cells. The transcriptional co-factor four and a half LIM domains 2 (FHL2) is a multifunctional adaptor protein that is involved in the regulation of gene expression, signal transduction and cell proliferation and differentiation, and also acts as a tumor suppressor or oncoprotein depending on the tissue microenvironment. The present study investigated the effect of plumbagin on FHL2 expression, Wnt/β-catenin signalling and its anti-proliferative activity in various human osteosarcoma cell lines, including SaOS2, MG63, HOS and U2OS. The cells were exposed to plumbagin and the expression of FHL2 was evaluated using western blot analysis. Furthermore, the anti-proliferative effect of plumbagin was evaluated using a 3-(4,5 dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. In addition, since FHL2 is involved in Wnt/β-catenin signaling, the effect of plumbagin on β-catenin and its primary target genes, including v-myc avian myelocytomatosis viral oncogene homolog (c-Myc) and WNT1 inducible signaling pathway protein-1 (WISP-1), was evaluated using western blot analysis. It was observed that plumbagin suppressed the expression of FHL2 and exhibited significant anti-proliferative activity in osteosarcoma cells. It also attenuated Wnt/β-catenin signalling by downregulating β-catenin and its target genes, including c-Myc and WISP-1. In conclusion, plumbagin demonstrated anti-proliferative activity in osteosarcoma cells by downregulating FHL2 and interfering with Wnt/β-catenin signalling.

Neuropeptide Y stimulates osteoblastic differentiation and VEGF expression of bone marrow mesenchymal stem cells related to canonical Wnt signaling activating in vitro

Neuropeptide Y (NPY) is a neuropeptide secreted by sensory nerve fibers distributed in the marrow and vascular canals of bone tissue. However, the effect of NPY on the osteogenic ability of bone marrow mesenchymal stem cells (BMSCs) remains controversial and has not been thoroughly investigated. To explore the osteogenic activity and the migration and VEGF expression capabilities of BMSCs affected by NPY, as well as the underlying mechanisms, we investigated the potential relationships among NPY, osteoblastic differentiation, angiogenesis and canonical Wnt signaling in BMSCs. NPY was observed to regulate osteoblastic differentiation at concentrations ranging from 10(-8) to 10(-12)mol/L, and the effects of NPY on the levels of Wnt signaling proteins were detected using Western blotting. To unravel the underlying mechanism, BMSCs were treated with NPY after pretreatment with the NPY-1R antagonist PD160170 or the Wnt pathway antagonist DKK1, and gene expression levels of Wnt signaling molecules and osteoblastic markers were determined by qPCR. Our results indicated that NPY significantly promoted osteoblastic differentiation of BMSCs in a concentration-dependent manner and up-regulated the expression levels of proteins including β-catenin and p-GSK-3β and the mRNA level of β-catenin. Moreover, NPY promoted the translocation of β-catenin into nucleus. The effects of NPY were inhibited by PD160170 or DKK1. Additionally, NPY enhanced the ability of BMSCs to migrate and promoted the expression of vascular endothelial growth factor (VEGF) as measured by immunocytochemical staining, qPCR and Western blot. These results suggested that NPY may stimulate osteoblastic differentiation via activating canonical Wnt signaling and enhance the angiogenic capacity of BMSCs.

Genome-Wide Chromatin Landscape Transitions Identify Novel Pathways in Early Commitment to Osteoblast Differentiation

Bone continuously undergoes remodeling by a tightly regulated process that involves osteoblast differentiation from Mesenchymal Stem Cells (MSC). However, commitment of MSC to osteoblastic lineage is a poorly understood process. Chromatin organization functions as a molecular gatekeeper of DNA functions. Detection of sites that are hypersensitive to Dnase I has been used for detailed examination of changes in response to hormones and differentiation cues. To investigate the early steps in commitment of MSC to osteoblasts, we used a model human temperature-sensitive cell line, hFOB. When shifted to non-permissive temperature, these cells undergo "spontaneous" differentiation that takes several weeks, a process that is greatly accelerated by osteogenic induction media. We performed Dnase I hypersensitivity assays combined with deep sequencing to identify genome-wide potential regulatory events in cells undergoing early steps of commitment to osteoblasts. Massive reorganization of chromatin occurred within hours of differentiation. Whereas ~30% of unique DHS sites were located in the promoters, the majority was outside of the promoters, designated as enhancers. Many of them were at novel genomic sites and need to be confirmed experimentally. We developed a novel method for identification of cellular networks based solely on DHS enhancers signature correlated to gene expression. The analysis of enhancers that were unique to differentiating cells led to identification of bone developmental program encompassing 147 genes that directly or indirectly participate in osteogenesis. Identification of these pathways provided an unprecedented view of genomic regulation during early steps of differentiation and changes related to WNT, AP-1 and other pathways may have therapeutic implications.

CARP-1/CCAR1: a biphasic regulator of cancer cell growth and apoptosis

Targeted cancer therapy using small molecule inhibitors (SMIs) has been useful in targeting the tumor cells while sparing the normal cells. Despite clinical success of many targeted therapies, their off-target effects and development of resistance are emerging as significant and challenging problems. Thus, there is an urgent need to identify targets to devise new means to treat cancers and their drug-resistant phenotypes. CARP-1/CCAR1 (Cell division cycle and apoptosis regulator 1), a peri-nuclear phospho-protein, plays a dynamic role in regulating cell growth and apoptosis by serving as a co-activator of steroid/thyroid nuclear receptors, β-catenin, Anaphase Promoting Complex/Cyclosome (APC/C) E3 ligase, and tumor suppressor p53. CARP-1/CCAR1 also regulates chemotherapy-dependent apoptosis. CARP-1/CCAR1 functional mimetics (CFMs) are a novel SMIs of CARP-1/CCAR1 interaction with APC/C. CFMs promote apoptosis in a manner independent of p53. CFMs are potent inhibitors of a variety of cancer cells including the drug (Adriamycin or Tamoxifen)-resistant breast cancer cells but not the immortalized breast epithelial cells, while a nano-lipid formulation of the lead compound CFM-4 improves its bioavailability and efficacy in vivo when administered orally. This review focuses on the background and pleiotropic roles of CARP-1/CCAR1 as well as its apoptosis signaling mechanisms in response to chemotherapy in cancer cells.

Identification of miR-194-5p as a potential biomarker for postmenopausal osteoporosis

The incidence of osteoporosis is high in postmenopausal women due to altered estrogen levels and continuous calcium loss that occurs with aging. Recent studies have shown that microRNAs (miRNAs) are involved in the development of osteoporosis. These miRNAs may be used as potential biomarkers to identify women at a high risk for developing the disease. In this study, whole blood samples were collected from 48 postmenopausal Chinese women with osteopenia or osteoporosis and pooled into six groups according to individual T-scores. A miRNA microarray analysis was performed on pooled blood samples to identify potential miRNA biomarkers for postmenopausal osteoporosis. Five miRNAs (miR-130b-3p, -151a-3p, -151b, -194-5p, and -590-5p) were identified in the microarray analysis. These dysregulated miRNAs were subjected to a pathway analysis investigating whether they were involved in regulating osteoporosis-related pathways. Among them, only miR-194-5p was enriched in multiple osteoporosis-related pathways. Enhanced miR-194-5p expression in women with osteoporosis was confirmed by quantitative reverse transcription–polymerase chain reaction analysis. For external validation, a significant correlation between the expression of miR-194-5p and T-scores was found in an independent patient collection comprised of 24 postmenopausal women with normal bone mineral density, 30 postmenopausal women with osteopenia, and 32 postmenopausal women with osteoporosis (p < 0.05). Taken together, the present findings suggest that miR-194-5p may be a viable miRNA biomarker for postmenopausal osteoporosis.

Identification of transcriptional factors and key genes in primary osteoporosis by DNA microarray

Background

A number of genes have been identified to be related with primary osteoporosis while less is known about the comprehensive interactions between regulating genes and proteins. We aimed to identify the differentially expressed genes (DEGs) and regulatory effects of transcription factors (TFs) involved in primary osteoporosis.

Material/Methods

The gene expression profile GSE35958 was obtained from Gene Expression Omnibus database, including 5 primary osteoporosis and 4 normal bone tissues. The differentially expressed genes between primary osteoporosis and normal bone tissues were identified by the same package in R language. The TFs of these DEGs were predicted with the Essaghir A method. DAVID (The Database for Annotation, Visualization and Integrated Discovery) was applied to perform the GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis of DEGs. After analyzing regulatory effects, a regulatory network was built between TFs and the related DEGs.

Results

A total of 579 DEGs was screened, including 310 up-regulated genes and 269 down-regulated genes in primary osteoporosis samples. In GO terms, more up-regulated genes were enriched in transcription regulator activity, and secondly in transcription factor activity. A total 10 significant pathways were enriched in KEGG analysis, including colorectal cancer, Wnt signaling pathway, Focal adhesion, and MAPK signaling pathway. Moreover, total 7 TFs were enriched, of which CTNNB1, SP1, and TP53 regulated most up-regulated DEGs.

Conclusions

The discovery of the enriched TFs might contribute to the understanding of the mechanism of primary osteoporosis. Further research on genes and TFs related to the WNT signaling pathway and MAPK pathway is urgent for clinical diagnosis and directing treatment of primary osteoporosis.

Circadian rhythms, Wnt/beta-catenin pathway and PPAR alpha/gamma profiles in diseases with primary or secondary cardiac dysfunction

Circadian clock mechanisms are far-from-equilibrium dissipative structures. Peroxisome proliferator-activated receptors (PPAR alpha, beta/delta, and gamma) play a key role in metabolic regulatory processes, particularly in heart muscle. Links between circadian rhythms (CRs) and PPARs have been established. Mammalian CRs involve at least two critical transcription factors, CLOCK and BMAL1 (Gekakis et al., 1998; Hogenesch et al., 1998). PPAR gamma plays a major role in both glucose and lipid metabolisms and presents circadian properties which coordinate the interplay between metabolism and CRs. PPAR gamma is a major component of the vascular clock. Vascular PPAR gamma is a peripheral regulator of cardiovascular rhythms controlling circadian variations in blood pressure and heart rate through BMAL1. We focused our review on diseases with abnormalities of CRs and with primary or secondary cardiac dysfunction. Moreover, these diseases presented changes in the Wnt/beta-catenin pathway and PPARs, according to two opposed profiles. Profile 1 was defined as follows: inactivation of the Wnt/beta-catenin pathway with increased expression of PPAR gamma. Profile 2 was defined as follows: activation of the Wnt/beta-catenin pathway with decreased expression of PPAR gamma. A typical profile 1 disease is arrhythmogenic right ventricular cardiomyopathy, a genetic cardiac disease which presents mutations of the desmosomal proteins and is mainly characterized by fatty acid accumulation in adult cardiomyocytes mainly in the right ventricle. The link between PPAR gamma dysfunction and desmosomal genetic mutations occurs via inactivation of the Wnt/beta-catenin pathway presenting oscillatory properties. A typical profile 2 disease is type 2 diabetes, with activation of the Wnt/beta-catenin pathway and decreased expression of PPAR gamma. CRs abnormalities are present in numerous pathologies such as cardiovascular diseases, sympathetic/parasympathetic dysfunction, hypertension, diabetes, neurodegenerative diseases, cancer which are often closely inter-related.

Vaccination with DKK1-derived peptides promotes bone formation and bone mass in an aged mouse osteoporosis model

The investigation of agents for the treatment of osteoporosis has been a long-standing effort. The Wnt pathway plays an important role in bone formation and regeneration, and expression of Wnt pathway inhibitors, Dickkopf-1 (DKK1), appears to be associated with changes in bone mass. Inactivation of DKK1 leads to substantially increased bone mass in genetically manipulated animals. DKK1-derived peptides (DDPs) were added to BMP2-stimulated MC3T3-E1 preosteoblastic cells in vitro to evaluate inhibitory activity of DDPs in MC3T3-E1 cell differentiation. Study was extended in vivo on old female mice to show whether or not inhibition of endogenous DKK1 biological activity using DDPs vaccination approach leads to increase of bone formation, bone density, and improvement of bone microstructure. We reported that synthetic DDPs were able to reduce alkaline phosphatase activity, prevent mineralization and inhibit the differentiation of MC3T3-E1 cells in vitro. Furthermore, vaccination with these DDPs in aged female mice 4 times for a total period of 22 weeks promoted bone mass and bone microstructure. 3D microCT and histomorphometric analysis showed that there were significant increase in bone mineral densities, improvement of bone microstructure and promotion of bone formation in the vaccinated mice, especially in the mice vaccinated with DDP-A and DDP-C. Histological and scanning electron microscopy image analysis also indicated that vaccination increased trabecular bone mass and significantly decreased fragmentation of bone fibers. Taken together, these preclinical results suggest that vaccination with DDPs represents a promising new therapeutic approach for the treatment of bone-related disorders, such as osteoporosis.

Vitamin D activities for health outcomes

Reports describing significant health risks due to inadequate vitamin D status continue to generate considerable interest amongst the medical and lay communities alike. Recent research on the various molecular activities of the vitamin D system, including the nuclear vitamin D receptor and other receptors for 1,25-dihydroxyvitamin D and vitamin D metabolism, provides evidence that the vitamin D system carries out biological activities across a wide range of tissues similar to other nuclear receptor hormones. This knowledge provides physiological plausibility of the various health benefits claimed to be provided by vitamin D and supports the proposals for conducting clinical trials. The vitamin D system plays critical roles in the maintenance of plasma calcium and phosphate and bone mineral homeostasis. Recent evidence confirms that plasma calcium homeostasis is the critical factor modulating vitamin D activity. Vitamin D activities in the skeleton include stimulation or inhibition of bone resorption and inhibition or stimulation of bone formation. The three major bone cell types, which are osteoblasts, osteocytes and osteoclasts, can all respond to vitamin D via the classical nuclear vitamin D receptor and metabolize 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D to activate the vitamin D receptor and modulate gene expression. Dietary calcium intake interacts with vitamin D metabolism at both the renal and bone tissue levels to direct either a catabolic action on the bone through the endocrine system when calcium intake is inadequate or an anabolic action through a bone autocrine or paracrine system when calcium intake is sufficient.

MiR-27a targets sFRP1 in hFOB cells to regulate proliferation, apoptosis and differentiation

MicroRNAs (miRNAs) play a key role in the regulation of almost all the physiological and pathological processes, including bone metabolism. Recent studies have suggested that miR-27 might play a key role in osteoblast differentiation and bone formation. Increasing evidence indicates that the canonical Wnt signaling pathway contributes to different stages of bone formation. In this study, we identify miR-27a can promote osteoblast differentiation by repressing a new target, secreted frizzled-related proteins 1 (sFRP1) expression at the transcriptional level. Here, 21 candidate targets of miR-27a involved in canonical Wnt/β-catenin signaling were predicted, and a significant decrease in sFRP1 luciferase activity was observed both in 293T and MG63 cells co-transfected with the matched luciferase reporter constructs and miR-27a mimic. Furthermore, the presence of exogenous miR-27a significantly decreased sFRP1 mRNA and protein expression in hFOB1.19 cells during both proliferation and osteogenic differentiation. The over-expression of miR-27a or knockdown sFRP1 significantly increased the percentage of apoptotic hFOBs, the percentage of cells in the G2-M phase of the cell cycle and the expression of key osteoblastic markers, including ALP, SPP1, RUNX2 and ALP activity. Over-expression of miR-27a or knockdown of endogenous sFRP1 led to an accumulation of β-catenin in hFOBs. In the present study, we demonstrate that miR-27a induced gene silencing effect is a vital mechanism contributing to bone metabolism in hFOB cells in vitro, which is partly affected by the post-transcriptional regulation of sFRP1, during osteoblast proliferation, apoptosis and differentiation.

Polymorphisms of the bovine DKK2 and their associations with body measurement traits and meat quality traits in Qinchuan cattle

The objective of this research were to detect bovine Dickkopf 2 (DKK2) gene polymorphism and analyze their associations with body measurement traits (BMT) and meat quality traits (MQT) of animals. Blood samples were taken from a total of 541 Qinchuan cattle aged from 18 to 24 months. Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) was employed to find out DKK2 single-polymorphism nucleotide (SNPs) and to explore their possible association with BMT and MQT. Sequence analysis of DKK2 gene revealed 2 SNPs (C29 T and A169C) in 5' untranslated region (5'UTR) of exon 1.C29T and A164T SNPs are both synonymous mutation, which showed 2 genotypes namely (CC, CT) and (AA and AC), respectively. Association analysis of polymorphism with body measurement and meat quality traits at the two locus showed that there were significant effects on CT, BL, RL, PBW, BFT, LMA, and IFC. These results suggest that the DKK2 gene might have potential effects on BMT and MQT in Qinchuan cattle population and could be used for marker-assisted selection.

Cell cycle and apoptosis regulatory protein (CARP)-1 is expressed in osteoblasts and regulated by PTH

Bone mass is dependent on osteoblast proliferation, differentiation and life-span of osteoblasts. Parathyroid hormone (PTH) controls osteoblast cell cycle regulatory proteins and suppresses mature osteoblasts apoptosis. Intermittent administration of PTH increases bone mass but the mechanism of action are complex and incompletely understood. Cell Cycle and Apoptosis Regulatory Protein (CARP)-1 (aka CCAR1) is a novel transducer of signaling by diverse agents including cell growth and differentiation factors. To gain further insight into the molecular mechanism, we investigated involvement of CARP-1 in PTH signaling in osteoblasts. Immunostaining studies revealed presence of CARP-1 in osteoblasts and osteocytes, while a minimal to absent levels were noted in the chondrocytes of femora from 10 to 12-week old mice. Treatment of 7-day differentiated MC3T3-E1 clone-4 (MC-4) mouse osteoblastic cells and primary calvarial osteoblasts with PTH for 30min to 5h followed by Western blot analysis showed 2- to 3-fold down-regulation of CARP-1 protein expression in a dose- and time-dependent manner compared to the respective vehicle treated control cells. H-89, a Protein Kinase A (PKA) inhibitor, suppressed PTH action on CARP-1 protein expression indicating PKA-dependent mechanism. PMA, a Protein Kinase C (PKC) agonist, mimicked PTH action, and the PKC inhibitor, GF109203X, partially blocked PTH-dependent downregulation of CARP-1, implying involvement of PKC. U0126, a Mitogen-Activated Protein Kinase (MAPK) Kinase (MEK) inhibitor, failed to interfere with CARP-1 suppression by PTH. In contrast, SB203580, p38 inhibitor, attenuated PTH down-regulation of CARP-1 suggesting that PTH utilized an Extracellular Signal Regulated Kinase (ERK)-independent but p38 dependent pathway to regulate CARP-1 protein expression in osteoblasts. Immunofluorescence staining of differentiated osteoblasts further revealed nuclear to cytoplasmic translocation of CARP-1 protein following PTH treatment. Collectively, our studies identified CARP-1 for the first time in osteoblasts and suggest its potential role in PTH signaling and bone anabolic action.

β-Sitosterol and flavonoids isolated from Bauhinia malabarica found during screening for Wnt signaling inhibitory activity

Screening with a cell-based luciferase assay was conducted to identify bioactive natural products which inhibit Wnt signaling activity-guided separation of an MeOH extract of Bauhinia malabarica (Caesalpiniaceae) leaves yielded five compounds, which were identified as β-sitosterol (1), quercetin (2), 6,8-C-dimethyl kaempferol-3-O-rhamnopyranoside (3), hyperin (4), and 6,8-C-dimethyl kaempferol-3-methyl ether (5). The tested compounds 1, 3, and 5 exhibited Wnt signaling inhibitory activity, with IC50 values of 0.77, 0.74, and 16.6 μM, respectively.

Genome-wide pathway association studies of multiple correlated quantitative phenotypes using principle component analyses

Genome-wide pathway association studies provide novel insight into the biological mechanism underlying complex diseases. Current pathway association studies primarily focus on single important disease phenotype, which is sometimes insufficient to characterize the clinical manifestations of complex diseases. We present a multi-phenotypes pathway association study(MPPAS) approach using principle component analysis(PCA). In our approach, PCA is first applied to multiple correlated quantitative phenotypes for extracting a set of orthogonal phenotypic components. The extracted phenotypic components are then used for pathway association analysis instead of original quantitative phenotypes. Four statistics were proposed for PCA-based MPPAS in this study. Simulations using the real data from the HapMap project were conducted to evaluate the power and type I error rates of PCA-based MPPAS under various scenarios considering sample sizes, additive and interactive genetic effects. A real genome-wide association study data set of bone mineral density (BMD) at hip and spine were also analyzed by PCA-based MPPAS. Simulation studies illustrated the performance of PCA-based MPPAS for identifying the causal pathways underlying complex diseases. Genome-wide MPPAS of BMD detected associations between BMD and KENNY_CTNNB1_TARGETS_UP as well as LONGEVITYPATHWAY pathways in this study. We aim to provide a applicable MPPAS approach, which may help to gain deep understanding the potential biological mechanism of association results for complex diseases.

Basic fibroblast growth factor inhibits osteogenic differentiation of stem cells from human exfoliated deciduous teeth through ERK signaling

OBJECTIVE

Stem cells from human exfoliated deciduous teeth (SHED) are a unique postnatal stem cell population capable of regenerating mineralized tissue and treating immune disorders. However, the mechanism that controls SHED differentiation is not fully understood. Here, we showed that basic fibroblast growth factor (bFGF) treatment attenuated SHED-mediated mineralized tissue regeneration through activation of the extracellular signal-regulated kinase (ERK) 1/2 pathway.

MATERIAL AND METHOD

The level of mineralized nodule formation was assessed by alizarin red staining. Expression levels of osteogenic genes, osteocalcin and runt-related transcription factor 2, were examined by RT-PCR. Subcutaneous implantation approach was used to assess in vivo bone formation. Downstream signaling pathways of bFGF were examined by Western blotting.

RESULT

Activation of ERK1/2 signaling by bFGF treatment inhibited WNT/β-catenin pathway, leading to osteogenic deficiency of SHED. ERK1/2 inhibitor treatment rescued bFGF-induced osteogenic differentiation deficiency.

CONCLUSION

These data suggest that bFGF inhibits osteogenic differentiation of SHED via ERK1/2 pathway. Blockade ERK1/2 signaling by small molecular inhibitor treatment improves bone formation of SHED after bFGF treatment.

Effects of one year daily teriparatide treatment on trabecular bone material properties in postmenopausal osteoporotic women previously treated with alendronate or risedronate

In the present work we examined the effect of teriparatide administration following bisphosphonate treatment on bone compositional properties by Raman and Fourier Transform Infrared Imaging (FTIR) microspectroscopic analysis. Thirty two paired iliac crest biopsies (before and after 1 year teriparatide) from sixteen osteoporotic women previously treated with either Alendronate (ALN) or Risedronate (RIS) and subsequently treated 12 months with teriparatide (TPTD) were analyzed at anatomical areas of similar tissue age in bone forming areas (within the fluorescent double labels). The outcomes that were monitored and reported were mineral to matrix ratio (corresponding to ash weight), mineral maturity (indicative of the mineral crystallite chemistry and stoichiometry, and having a direct bearing on crystallite shape and size), relative proteoglycan content (regulating mineralization commencement), and the ratio of two of the major enzymatic collagen cross-links (pyridinoline/divalent). Significant differences in mineral/matrix, mineral maturity/crystallinity, and collagen cross-link ratio bone quality indices after TPTD treatment were observed, indicating a specific response of these patients to TPTD treatment. Moreover differences between ALN and RIS treated patients at baseline in the collagen cross-link ratio were observed. Since tissue areas of similar tissue age were analyzed, these differences may not be attributed to differences in bone turnover.

Association between Wnt signaling pathway gene polymorphisms and bone response to hormone therapy in postmenopausal Korean women

OBJECTIVE

The aim of this study was to explore the association between Wnt signaling pathway gene polymorphisms and response to hormone therapy (HT) as related to bone mineral density (BMD) in postmenopausal Korean women.

METHODS

The BMD and serum levels of osteoprotegerin, the soluble receptor activator of the nuclear factor κB ligand, and bone turnover markers were measured in 308 postmenopausal women receiving sequential estrogen + progestogen therapy. Results were analyzed according to the low-density lipoprotein receptor--related protein (LRP5) 5 c.266A > G, c.3893C > T, frizzled receptor 6 gene c.1033A > C, axin II c.148C > T, adenomatous polyposis coli c.5645T > A, and T-cell factor 1 c.766G > A polymorphisms.

RESULTS

The rates of 1-year changes in BMD and changes at 6 months in osteoprotegerin, soluble receptor activator of the nuclear factor κB ligand, and bone turnover markers after HT did not differ significantly between all single and haplotype genotypes of the genes studied. When a nonresponder was defined as a woman who had lost more than 3% of BMD per year after HT, women with T allele of the LRP5 c.3893C > T polymorphism showed a significantly higher risk of nonresponse at both the lumbar spine and femoral neck than did women with C allele. The risk of nonresponse at the lumbar spine was significantly higher in women with G allele of the LRP5 c.266A > G polymorphism than that in women with A allele, and the c.266G/c.3893T (GT) haplotype allele showed a similar trend.

CONCLUSIONS

The LRP5 c.266A > G and c.3893C > T polymorphisms may be associated with risk of nonresponse to HT in postmenopausal Korean women.

Evolution of the parathyroid hormone family and skeletal formation pathways

Bone is considered to be a feature of higher vertebrates and one of the features that was required for the movement from water onto land. But there are a number of evolutionarily important species that have cartilaginous skeletons, including sharks. Both bony and cartilaginous fish are believed to have a common ancestor who had a bony skeleton. A number of factors and pathways have been shown to be involved in the development and maintenance of bony skeleton including the Wnt pathway and the parathyroid hormone gene family. The study of these pathways and factors in cartilaginous animals may shed light on the evolution of the vertebrate skeleton.

Calcitonin gene-related peptide (CGRP) inhibits apoptosis in human osteoblasts by β-catenin stabilization

Transgenic mice over-expressing calcitonin gene-related peptide (CGRP) in osteoblasts have increased bone density due to increased bone formation, thus suggesting that CGRP plays a role in bone metabolism. In this study we determined the relationship between CGRP, the canonical Wnt signaling and apoptosis in human osteoblasts (hOBs) in consideration of the well-documented involvement of this pathway in bone cells. Primary cultures of hOBs were treated with CGRP 10(-8) M. Levels of β-catenin, which is the cytoplasmic protein mediator of canonical Wnt signaling, and mRNA were determined. CGRP increases both the expression and the levels of cytoplasmic β-catenin by binding to its receptor, as this effect is blocked by the antagonist CGRP(8-37). This facilitatory action on β-catenin appears to be mediated by the inhibition of the enzyme GSK-3β via protein kinase A (PKA) activation. GSK-3β is a glycogen synthase kinase that, by phosphorylating β-catenin, promotes its degradation by the proteosomal machinery. Moreover, the peptide is able to inhibit hOBs apoptosis stimulated by dexamethasone or by serum deprivation, possibly through the accumulation of β-catenin, since the inhibitor of PKA activity H89 partially prevents the antiapoptotic effect of the peptide. In conclusion CGRP, released by nerve fibers, exerts its anabolic action on bone cells by stimulating canonical Wnt signaling and by inhibiting hOBs apoptosis, thus favoring local bone regeneration.

Transgenic mice overexpressing secreted frizzled-related proteins (sFRP)4 under the control of serum amyloid P promoter exhibit low bone mass but did not result in disturbed phosphate homeostasis

Secreted frizzled-related protein-4 (sFRP4) is a member of secreted modulators of Wnt signaling pathways and has been recognized to play important role in the pathogenesis of oncogenic osteomalacia as a potential phosphatonin. To investigate the role of sFRP4 in bone biology and phosphorus homeostasis in postnatal life, we generated transgenic mice that overexpress sFRP4 under the control of the serum amyloid P promoter (SAP-sFRP4), which drives transgene expression postnatally. Serum phosphorus level and urinary phosphorus excretion were slightly lower and higher, respectively, in SAP-sFRP4 compared to wild-type (WT) littermate, but the difference did not reach statistical significance. However, renal Na(+/-)/Pi co-transporter (Npt) 2a and 1alpha-hydroxylase gene expression were up-regulated in SAP-sFRP4 mice. In addition, the level of serum 1,25-dihydroxyvitamin D(3) was higher in SAP-sFRP4 mice. At 5 weeks of age, bone mineral density (BMD) in SAP-sFRP4 was similar to that in WT. However, with advancing age, SAP-sFRP4 mice gained less BMD so that areal BMD of SAP-sFRP4 mice was significantly lower compared to WT at 15 weeks of age. Histomorphometric analysis of proximal tibia showed that trabecular bone volume (BV/TV) and thickness (Tb.Th) were significantly lower in SAP-sFRP4 mice. There was no evidence of osteomalacia in histological analysis. Our data do not support the role of sFRP4 per se as a phosphatonin but suggest that sFRP4 negatively regulates bone formation without disrupting phosphorus homeostasis.

miR-29 modulates Wnt signaling in human osteoblasts through a positive feedback loop

Differentiation of human mesenchymal stem cells into osteoblasts is controlled by extracellular cues. Canonical Wnt signaling is particularly important for maintenance of bone mass in humans. Post-transcriptional regulation of gene expression, mediated by microRNAs, plays an essential role in the control of osteoblast differentiation. Here, we find that miR-29a is necessary for human osteoblast differentiation, and miR-29a is increased during differentiation in the mesenchymal precursor cell line hFOB1.19 and in primary cultures of human osteoblasts. Furthermore, the promoter of the expressed sequence tag containing the human miR-29a gene is induced by canonical Wnt signaling. This effect is mediated, at least in part, by two T-cell factor/LEF-binding sites within the proximal promoter. Furthermore, we show that the negative regulators of Wnt signaling, Dikkopf-1 (Dkk1), Kremen2, and secreted frizzled related protein 2 (sFRP2), are direct targets of miR-29a. Endogenous protein levels for these Wnt antagonists are increased in cells transfected with synthetic miR-29a inhibitor. In contrast, transfection with miR-29a mimic decreases expression of these antagonists and potentiates Wnt signaling. Overall, we demonstrate that miR-29 and Wnt signaling are involved in a regulatory circuit that can modulate osteoblast differentiation. Specifically, canonical Wnt signaling induces miR-29a transcription. The subsequent down-regulation of key Wnt signaling antagonists, Dkk1, Kremen2, and sFRP2, by miR-29a potentiates Wnt signaling, contributing to a gene expression program important for osteoblast differentiation. This novel regulatory circuit provides additional insight into how microRNAs interact with signaling molecules during osteoblast differentiation, allowing for fine-tuning of intricate cellular processes.