Sclerostin: current knowledge and future perspectives

PTH1-34 blocks radiation-induced osteoblast apoptosis by enhancing DNA repair through canonical Wnt pathway

Focal radiotherapy for cancer patients has detrimental effects on bones within the radiation field and the primary clinical signs of bone damage include the loss of functional osteoblasts. We reported previously that daily injection of parathyroid hormone (PTH, 1-34) alleviates radiation-induced osteopenia in a preclinical radiotherapy model by improving osteoblast survival. To elucidate the molecular mechanisms, we irradiated osteoblastic UMR 106-01 cells and calvarial organ culture and demonstrated an anti-apoptosis effect of PTH1-34 on these cultures. Inhibitor assay indicated that PTH exerts its radioprotective action mainly through protein kinase A/β-catenin pathway. γ-H2AX foci staining and comet assay revealed that PTH efficiently promotes the repair of DNA double strand breaks (DSBs) in irradiated osteoblasts via activating the β-catenin pathway. Interestingly, Wnt3a alone also blocked cell death and accelerated DNA repair in primary osteoprogenitors, osteoblastic and osteocytic cells after radiation through the canonical signaling. Further investigations revealed that both Wnt3a and PTH increase the amount of Ku70, a core protein for initiating the assembly of DSB repair machinery, in osteoblasts after radiation. Moreover, down-regulation of Ku70 by siRNA abrogated the prosurvival effect of PTH and Wnt3a on irradiated osteoblasts. In summary, our results identify a novel role of PTH and canonical Wnt signaling in regulating DSB repair machinery and apoptosis in osteoblasts and shed light on using PTH1-34 or Wnt agonist as possible therapy for radiation-induced osteoporosis.

Serum sclerostin in high-activity adult patients with juvenile idiopathic arthritis

Introduction

Juvenile idiopathic arthritis (JIA) is a disease associated with loss of bone mass, deterioration in bone mass quality and an increased risk of fractures. The objective of this study was to evaluate factors that predict bone mineral density (BMD) alterations in young adult patients with active JIA before and during therapy with tumour necrosis factor α (TNFα) inhibitors.

Methods

Thirty-one patients (twelve males and nineteen females; mean age =25.1 ± 6.1 years) with active JIA (mean Disease Activity Score in 28 joints (DAS28) =6.36 ± 0.64; mean high-sensitivity C-reactive protein (hsCRP) =18.36 ± 16.95 mg/L) were investigated. The control group consisted of 84 healthy individuals matched by sex and age. BMD, bone turnover markers and serum concentrations of soluble receptor activator of nuclear factor κB ligand, osteoprotegerin, dickkopf Wnt signalling pathway inhibitor 1 (Dkk1) and sclerostin were evaluated.

Results

Baseline BMD values in the lumbar spine, proximal femur, femoral neck and distal radius were significantly lower in patients with JIA compared to healthy control participants. Baseline sclerostin serum concentrations were significantly higher in patients with JIA compared to control participants. After 2 years of treatment with TNFα inhibitors, BMD was significantly increased in the lumbar spine. This increase correlated with a drop in DAS28 score. A statistically significant correlation between hsCRP and Dkk1 was found at baseline, as well as during the 2-year follow-up period. A significant reduction in serum sclerostin after 1 year of therapy was predictive of a drop in DAS28 score observed with a 1-year delay after reduction of serum sclerostin.

Conclusion

A significant correlation between the sclerostin serum concentration and the number of tender and swollen joints, but not BMD, supports the hypothesis that chondrocytes and cells of the subchondral bone may contribute to circulating sclerostin in JIA.

Sclerostin deficiency is linked to altered bone composition

High bone mass in animals and humans with sclerostin deficiency is associated with increased bone strength, which is not the case for all disorders with high bone mineral density, some of which are even associated with fragility fractures owing to unfavorable bone composition. In the current study we investigated whether alterations in bone composition may contribute to the bone strength characteristics associated with lack of sclerostin. We examined cortical bone of Sost-knockout (KO) mice (n = 9, 16 weeks old) and sclerosteosis patients (young [4 to 14 years], n = 4 and adults [24 and 43 years], n = 2) by quantitative backscattered electron imaging and Raman microspectroscopy and compared it to bone from wild-type mice and healthy subjects, respectively. In Sost-KO mice endocortical bone exhibited altered bone composition, whereas subperiosteal bone was unchanged. When comparing endocortical bone tissue of identical tissue age as defined by sequential dual fluorochrome labeling the average bone matrix mineralization was reduced -1.9% (p < 0.0001, younger tissue age) and -1.5% (p < 0.05, older tissue age), and the relative proteoglycan content was significantly increased. Similarly, bone matrix mineralization density distribution was also shifted toward lower matrix mineralization in surgical samples of compact bone of sclerosteosis patients. This was associated with an increase in mineralization heterogeneity in the young population. In addition, and consistently, the relative proteoglycan content was increased. In conclusion, we observed decreased matrix mineralization and increased relative proteoglycan content in bone subcompartments of Sost-KO mice-a finding that translated into sclerosteosis patients. We hypothesize that the altered bone composition contributes to the increased bone strength of patients with sclerostin deficiency.

A review of osteocyte function and the emerging importance of sclerostin

➤ Osteocytes, derived from osteoblasts, reside within bone and communicate extensively with other bone cell populations to regulate bone metabolism. The mature osteocyte expresses the protein sclerostin, a negative regulator of bone mass.➤ In normal physiologic states, the protein sclerostin acts on osteoblasts at the surface of bone and is differentially expressed in response to mechanical loading, inflammatory molecules such as prostaglandin E2, and hormones such as parathyroid hormone and estrogen.➤ Pathologically, sclerostin dysregulation has been observed in osteoporosis-related fractures, failure of implant osseous integration, metastatic bone disease, and select genetic diseases of bone mass.➤ An antibody that targets sclerostin, decreasing endogenous levels of sclerostin while increasing bone mineral density, is currently in phase-III clinical trials.➤ The osteocyte has emerged as a versatile, indispensable bone cell. Its location within bone, extensive dendritic network, and close communication with systemic circulation and other bone cells produce many opportunities to treat a variety of orthopaedic conditions.

Biological agents in management of osteoporosis

Osteoporosis is a skeletal disease associated with an imbalance between formation and resorption, leading to net loss of bone mass, loss of bone microarchitecture, and development of fractures. Bone resorption is primarily due to an activation of osteoclastogenesis and an increase in receptor activator of nuclear factor kappa-B ligand (RANKL) expression, a cytokine involved in the final pathway of the osteoclast cycle.Recent studies of genetic diseases led to the discovery of the wingless-type (Wnt) signaling pathway that plays a major role in bone formation. Further work showed that sclerostin produced by osteocytes and the Dickkopf (DKK1) protein secreted in bone were negative regulators of the Wnt signaling bone formation pathway that act directly by binding to the co-receptors LRP5 and LRP6 of WnT and thereby inhibiting the anabolic Wnt pathway. This understanding of the bone remodeling led to the discovery of new biological drugs that target these pathways and have been evaluated in clinical trials.The current article discusses the role of these newer "biological" agents in management of osteoporosis. Denosumab, a human monoclonal antibody that specifically binds RANKL, blocks the binding of RANK to its ligand markedly reducing bone resorption, increases bone density, and reduces fractures and is approved for osteoporosis. Parathyroid hormone PTH 1-34 (teriparatide) stimulates bone formation through inhibition of sclerostin, DKK1, and frizzled protein; increases BMD; improves microarchitecture; and decreases fractures and is approved for osteoporosis. The anti-sclerostin antibodies (romosozumab, blosozumab) increase bone mass by neutralizing the negative effects of sclerostin on the Wnt signaling pathway. These biologics are being evaluated now in a clinical trial and early data looks promising. Cathepsin K is a proteolytic enzyme that degrades bone matrix and inhibitors such as odanacatib show increasing bone density and perhaps decreased fractures. The potential power of combining these newer antiresorptives with the newer anabolic agents could theoretically increase bone mass rapidly to normal within 1 year and reduce fractures. These newer treatments are revolutionizing the management of osteoporosis.

Gender differences in sclerostin and clinical characteristics in type 1 diabetes mellitus

BACKGROUND

Sclerostin is an osteocyte-derived inhibitor of the Wnt/β-catenin signaling pathway, which acts as a negative regulator of bone formation. Published data on sclerostin levels in type 1 diabetes mellitus (T1DM) are few.

OBJECTIVE

To evaluate gender differences in sclerostin serum levels and the association among sclerostin, bone mass, bone metabolism, and the main clinical characteristics of subjects with T1DM.

DESIGN AND METHODS

A total of 69 patients with T1DM (mean age, 33.7±8.1; 49% males) were enrolled in this cross-sectional study in a clinical research center. Bone mineral density was measured by phalangeal quantitative ultrasound (QUS); bone turnover markers (urinary pyridinoline, deoxypyridinoline (D-PYR), and urine hydroxyproline (OH-PRO) to evaluate bone resorption; serum bone alkaline phosphatase and BGP to evaluate bone formation) and sclerostin were assessed.

RESULTS

D-PYR and sclerostin were significantly higher in women when compared with men (P=0.04). A disease duration >15 years was associated with higher sclerostin levels (P=0.03). Bone turnover markers and QUS parameters were not correlated with sclerostin. A significant negative correlation was observed among QUS parameters, BMI, and OH-PRO. Sclerostin serum levels were correlated with homocysteine (r=-0.34, P=0.005) and vitamin B12 (r=-0.31, P=0.02). Generalized linear model showed that macroangiopathy was the only predictor of sclerostin serum levels (β=-11.8, 95% CI from -21.9 to -1.7; P=0.02).

CONCLUSIONS

Our data demonstrate that women with T1DM exhibit higher sclerostin levels than men and that circulating sclerostin is not associated with bone turnover markers and phalangeal QUS measurements. Macroangiopathy was associated with sclerostin levels.

Relationship between insulin sensitivity and bone mineral density in primary hyperparathyroidism

INTRODUCTION

Evidence of crosstalk between bone and insulin metabolism has been identified. In primary hyperparathyroidism (PHPT), scant data exist on this relationship.

AIM

To evaluate the relationship between insulin levels or sensitivity and bone mineral density (BMD) in PHPT.

SUBJECT AND METHODS

Two hundred and sixty-seven patients with PHPT without known diabetes mellitus were studied. Fasting blood glucose and insulin levels as well as BMD at lumbar spine, femoral neck and forearm were measured. Insulin sensitivity was assessed using Quantitative Insulin Sensitivity Check Index (QUICKI). The same parameters were measured 2 years (interquartile range 2·8 years) after surgery (PTX) in a subgroup of patients (n = 51).

RESULTS

In univariate analysis, a positive relationship between insulin levels and BMD (R = 0·17, P < 0·03) or T-score (R = 0·20, P < 0·005) was found at femoral neck level. Consequently, a negative relationship between QUICKI and femoral BMD (R = -0·20, P < 0·01) or T-score (R = -0·21, P < 0·004) was found. In multivariate analysis, when femoral BMD was the dependent variable, age (beta = -0·35, P < 0·000004), BMI (beta = 0·39, P < 0·00001), PTH (beta = -0·18, P < 0·05) and QUICKI (R = -0·15, P < 0·05) had an independent effect (R(2) = 0·29). Insulin levels and QUICKI did not change after PTX. No relationship was found between QUICKI or insulin levels at the time of diagnosis and change in BMD at any site at follow-up.

CONCLUSIONS

Our data show a weak relationship between insulin levels and/or insulin sensitivity and BMD in PHPT. However, the insulin state does not influence change in bone density after PTX in PHPT.

Class I and IIa histone deacetylases have opposite effects on sclerostin gene regulation

Adult bone mass is controlled by the bone formation repressor sclerostin (SOST). Previously, we have shown that intermittent parathyroid hormone (PTH) bone anabolic therapy involves SOST expression reduction by inhibiting myocyte enhancer factor 2 (MEF2), which activates a distant bone enhancer. Here, we extended our SOST gene regulation studies by analyzing a role of class I and IIa histone deacetylases (HDACs), which are known regulators of MEF2s. Expression analysis using quantitative PCR (qPCR) showed high expression of HDACs 1 and 2, lower amounts of HDACs 3, 5, and 7, low amounts of HDAC4, and no expression of HDACs 8 and 9 in constitutively SOST-expressing UMR106 osteocytic cells. PTH-induced Sost suppression was associated with specific rapid nuclear accumulation of HDAC5 and co-localization with MEF2s in nuclear speckles requiring serine residues 259 and 498, whose phosphorylations control nucleocytoplasmic shuttling. Increasing nuclear levels of HDAC5 in UMR106 by blocking nuclear export with leptomycin B (LepB) or overexpression in transient transfection assays inhibited endogenous Sost transcription and reporter gene expression, respectively. This repressor effect of HDAC5 did not require catalytic activity using specific HDAC inhibitors. In contrast, inhibition of class I HDAC activities and expression using RNA interference suppressed constitutive Sost expression in UMR106 cells. An unbiased comprehensive search for involved HDAC targets using an acetylome analysis revealed several non-histone proteins as candidates. These findings suggest that PTH-mediated Sost repression involves nuclear accumulation of HDAC inhibiting the MEF2-dependent Sost bone enhancer, and class I HDACs are required for constitutive Sost expression in osteocytes.

Prevention of incident fractures in patients with prevalent fragility fractures: Current and future approaches

Fragility fractures are a significant, independent risk factor for new fractures, but treatment uptake in subjects with prevalent fractures is disappointing. We addressed the question of the efficacy of pharmacological interventions in reducing the risk of incident fractures in patients with prevalent fragility fractures. For this, we reviewed randomised controlled trials (RCTs), pre-planned and post-hoc analyses of RCTs of approved agents for the treatment of osteoporosis. Results showed that a number of agents decrease the risk of incident vertebral and nonvertebral fractures in subjects with prevalent vertebral fractures, justifying the recommendation of treating such patients independently of the level of bone mineral density (BMD). By contrast, the evidence of antifracture efficacy of these agents in patients with prevalent nonvertebral fractures is limited. Advances in our understanding of the regulation of bone metabolism at the molecular level have identified targets for the development of new therapeutics for osteoporosis, some of which are currently in phase 3 clinical development.

The osteocyte as a therapeutic target in the treatment of osteoporosis

Osteoporosis is characterized by a low bone-mineral density associated with skeletal fractures. The decrease in bone-mineral density is the consequence of an unbalanced bone-remodeling process, with higher bone resorption than bone formation. The orchestration of the bone-remodeling process is under the control of the most abundant cell in bone, the osteocyte. Functioning as an endocrine cell, osteocytes are also a source of soluble factors that not only target cells on the bone surface, but also target distant organs. Therefore, any drugs targeting the osteocyte functions and signaling pathways will have a major impact on the bone-remodeling process. This review discusses potential advances in drug therapy for osteoporosis, including novel osteocyte-related antiresorptive and anabolic agents that may become available in the coming years.

Strontium promotes cementoblasts differentiation through inhibiting sclerostin expression in vitro

Cementogenesis, performed by cementoblasts, is important for the repair of root resorption caused by orthodontic treatment. Based on recent studies, strontium has been applied for osteoporosis treatment due to its positive effect on osteoblasts. Although promising, the effect of strontium on cementoblasts is still unclear. So the aim of this research was to clarify and investigate the effect of strontium on cementogenesis via employing cementoblasts as model. A series of experiments including MTT, alkaline phosphatase activity, gene analysis, alizarin red staining, and western blot were carried out to evaluate the proliferation and differentiation of cementoblasts. In addition, expression of sclerostin was checked to analyze the possible mechanism. Our results show that strontium inhibits the proliferation of cementoblasts with a dose dependent manner; however, it can promote the differentiation of cementoblasts via downregulating sclerostin expression. Taking together, strontium may facilitate cementogenesis and benefit the treatment of root resorption at a low dose.

[Interaction between myeloma cells and bone tissue]

BACKGROUND

Multiple myeloma is the malignant disease which most frequently leads to bone lesions. Approximately 80% of myeloma patients develop osteoporosis, lytic bone lesions (osteolysis) or fractures during the course of the disease. Of these patients 43% suffer pathological fractures most often of the vertebrae followed by fractures of the long bones.

MATERIAL AND METHODS

The methods used in the described articles include, e.g. gene expression profiling, enzyme-linked immunosorbent assays and radiological techniques.

RESULTS AND DISCUSSION

Myeloma bone disease represents a threefold therapeutic problem: (i) per se because of the associated morbidity, mortality and the accompanying decrease of quality of life, (ii) as survival space for (residual) myeloma cells after primarily successful chemotherapy and subsequently necessary chemotherapeutic treatment, and (iii) the occurrence of bone lesions in asymptomatic patients is the most common cause for the initiation of treatment to avoid myeloma-induced fractures. Myeloma cells harbor a high median number of chromosomal aberrations and multiple changes in gene expression compared to normal bone marrow plasma cells leading to the aberrant production of survival, proliferation, pro-angiogenic and bone turnover influencing factors or the induction of those factors in the bone marrow microenvironment. This causes an imbalanced bone turnover in the sense of an increased number and activity of osteoclasts while bone formation by osteoblasts is almost completely suspended. Therapeutic approaches, systemically and locally therefore aim at stimulation of osteoblasts and inhibition of bone resorption.

Clinical and endocrine correlates of circulating sclerostin levels in patients with type 1 diabetes mellitus

AIM

Type 1 diabetes mellitus (T1DM) increases fragility fractures due to low bone mass, micro-architectural alterations and decreased bone formation. Sclerostin is expressed by osteocytes and inhibits osteoblastic bone formation. We evaluated serum sclerostin levels in T1DM and their association with bone mineral density (BMD), bone turnover, glycaemic control and physical activity.

PATIENTS AND METHODS

In a cross-sectional study, 128 men and premenopausal women with long-standing T1DM (mean age 43·4 ± 8·8 years, diabetes duration 22·4 ± 9·5 years) and 77 age-, BMI (Body Mass Index) and gender-matched healthy individuals were evaluated.

RESULTS

Serum sclerostin levels were higher in T1DM compared with controls, irrespective of gender (male 0·55 ± 0·17 vs 0·49 ± 0·12 ng/ml, P = 0·046; female 0·52 ± 0·19 ng/ml vs 0·43 ± 0·12 ng/ml, P = 0·012). Partial correlation analysis adjusted for age and gender revealed a positive correlation between serum sclerostin levels and BMD at lumbar spine and femoral neck in T1DM and between BMD at lumbar spine, femoral neck and total hip in controls. Bone turnover markers, parathyroid hormone, calcium and vitamin D did not correlate with serum sclerostin levels in T1DM or controls. Physical activity was not associated with serum sclerostin levels. A multivariate analysis revealed that only the interaction of T1DM and age affects serum sclerostin levels but not T1DM alone. The influence of age on serum sclerostin levels was more pronounced in T1DM compared with controls.

CONCLUSIONS

Sclerostin serum levels were increased in patients with T1DM, and the positive correlation of age with serum sclerostin levels was stronger in T1DM. There was no effect of serum sclerostin levels on markers of bone metabolism and they do not explain the detrimental effects of T1DM on BMD.

The effect of dried plum on serum levels of receptor activator of NF-κB ligand, osteoprotegerin and sclerostin in osteopenic postmenopausal women: a randomised controlled trial

Although several studies have confirmed the bone-protective properties of dried plum, its exact mechanisms of action remain unclear. Recent research has shown that osteocytes may control bone formation via the production of sclerostin and bone resorption via the receptor activator of NF-κB ligand (RANKL) and its inhibitor osteoprotegerin (OPG). To investigate the mechanism of action of dried plum in reversing bone loss, we measured serum levels of RANKL, OPG and sclerostin in osteopenic postmenopausal women (n 160). Participants were randomly assigned to the treatment group of either 100 g dried plum/d or 75 g dried apple/d (comparative control) for 1 year. All participants received 500 mg Ca plus 400 IU (10 μg) vitamin D daily. Bone mineral densities (BMD) of the lumbar spine, forearm, hip and whole body were assessed at baseline and at the end of the study using dual-energy X-ray absorptiometry. Blood samples were collected at baseline and after 12 months to assess bone biomarkers. Dried plum significantly increased the BMD of the ulna and spine in comparison with the control group. In comparison with corresponding baseline values, dried plum increased the RANKL levels by only +1·99 v. +18·33% and increased the OPG levels by +4·87 v. - 2·15% in the control group. Serum sclerostin levels were reduced by - 1·12% in the dried plum group v. +3·78% in the control group. Although percentage changes did not reach statistical significance (P≤ 0·05), these preliminary data may indicate that the positive effects of dried plum on bone are in part due to the suppression of RANKL production, the promotion of OPG and the inhibition of sclerostin.

Expression of fibroblast growth factor 23, vitamin D receptor, and sclerostin in bone tissue from hypercalciuric stone formers

BACKGROUND AND OBJECTIVES

Increased bone resorption, low bone formation, and abnormal mineralization have been described in stone formers with idiopathic hypercalciuria. It has been previously shown that the receptor activator of NF-κB ligand mediates bone resorption in idiopathic hypercalciuria (IH). The present study aimed to determine the expression of fibroblast growth factor 23 (FGF-23), vitamin D receptor (VDR), and sclerostin in bone tissue from IH stone formers.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Immunohistochemical analysis was performed in undecalcified bone samples previously obtained for histomorphometry from 30 transiliac bone biopsies of idiopathic hypercalciuria stone-forming patients between 1992 and 2002 and 33 healthy individuals (controls). Serum parameters were obtained from their medical records.

RESULTS

Histomorphometry disclosed 21 IH patients with high and 9 IH patients with normal bone resorption. Importantly, eroded surfaces (ES/BS) from IH patients but not controls were significantly correlated with VDR immunostaining in osteoblasts (r=0.51; P=0.004), sclerostin immunostaining in osteocytes (r=0.41; P=0.02), and serum 1,25-dihydroxyvitamin D (r=0.55; P<0.01). Of note, both VDR and sclerostin immunostaining were significantly correlated with serum 1,25-dihydroxyvitamin D in IH patients (r=0.52; P=0.01 and r=0.53; P=0.02, respectively), although VDR and sclerostin expression did not differ between IH and controls. IH patients with high bone resorption exhibited a significantly stronger sclerostin immunostaining than IH patients with normal bone resorption. FGF-23 expression in osteocytes from IH patients did not differ from controls and was not correlated with any histomorphometric parameter.

CONCLUSIONS

These findings suggest the contribution of VDR and sclerostin, as well as 1,25-dihydroxyvitamin D, to increase bone resorption in idiopathic hypercalciuria but do not implicate FGF-23 in the bone alterations seen in these patients.

Effects of intravenous zoledronate and ibandronate on carotid intima-media thickness, lipids and FGF-23 in postmenopausal osteoporotic women

OBJECTIVE

Osteoporosis and atherosclerosis are interconnected entities and share also some pathophysiological mechanisms. Moreover, recent literature data have supported the hypothesis that bisphosphonates (BPs) may have some antiatherogenic actions. This study aimed to evaluate the effects of one year with zoledronate or ibandronate given intravenously on lipid profile and on carotid artery intima-media thickness (CA-IMT).

METHODS

Sixty postmenopausal osteoporotic women (mean age: 66.6±7.8years) were randomly assigned to 1-year treatment with zoledronate 5mg i.v. annually or ibandronate 3mg i.v. every 3 months. In all patients at baseline and after 12months we measured CA-IMT, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), 25-hydroxyvitamin D (25OHD), bone alkaline phosphatase (B-ALP), type I collagen β carboxy telopeptide (βCTX), osteocalcin (OC), fibroblast growth factor 23 (FGF-23) and sclerostin.

RESULTS

The osteoporotic women treated with zoledronate showed a greater reduction in CA-IMT than those treated with ibandronate. HDL-C and HDL-C/LDL-C ratio showed a significant (p<0.01) increase in the 2 groups, whereas, LDL-C showed a reduction in the two groups which, however, reached statistical significance (p<0.05) only in the zoledronate group. FGF-23 serum levels showed a similar and significant decrease in both the women treated with zoledronate and in those treated with ibandronate. At the end of the study period sclerostin serum levels showed a higher increase in the patients treated with zoledronate than in those treated with ibandronate.

CONCLUSION

In osteoporotic women both zoledronate and ibandronate given intravenously resulted in an increase in HDL-C/LDL-C ratio and a reduction of CA-IMT which was significant only for zoledronate. Further prospective studies are needed to clarify whether the change in FGF-23 and sclerostin levels is a marker or a potential mechanism of the action of BPs at a vascular level.

Update on romosozumab : a humanized monoclonal antibody to sclerostin

INTRODUCTION

Disorders with inactivating mutations of the SOST gene result in reduced or absent expression of sclerostin and are associated with high bone mass. Sclerostin is an important regulator of bone formation due to its inhibitory actions in the osteoanabolic Wnt signaling pathway. Advances in understanding the mechanisms of action of this signaling molecule have led to the development of a pharmacological inhibitor of sclerostin with potential clinical applications as an osteoanabolic drug for the treatment of osteoporosis.

AREAS COVERED

Romosozumab is the first humanized monoclonal sclerostin antibody to be tested in clinical trials. Similar to preclinical animal studies with sclerostin antibodies, initial clinical studies show that romosozumab increases bone formation and bone mineral density.

EXPERT OPINION

Blocking sclerostin action with romosozumab is a promising new therapeutic approach to osteoanabolic therapy of osteoporosis; efficacy and safety data on large controlled studies are awaited.

Osteocytes produce interferon-β as a negative regulator of osteoclastogenesis

Osteoclastogenesis is controlled by osteocytes; osteocytic osteoclastogenesis regulatory molecules are largely unknown. We searched for such factors using newly developed culture methods. Our culture system mimics the three-dimensional cellular structure of bone, consisting of collagen gel-embedded osteocytic MLO-Y4 cells, stromal ST2 cells on the gel as bone lining cells, and bone marrow cells. The gel-embedded MLO-Y4 cells inhibited the osteoclastogenesis induced by 1,25(OH)2D3 without modulating receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) production by ST2 cells, despite MLO-Y4 cells supported osteoclastogenesis in the absence of ST2 cells. In the bone marrow cell culture, the conditioned medium from MLO-Y4 cells decreased the capability of osteoclastic differentiation from the cells induced by macrophage colony-stimulating factor. This decreased capability was concomitant with an increase in protein kinase R mRNA expression and an inhibition of c-Fos translation. These changes were partially normalized by the simultaneous addition of an anti-interferon (IFN)-β neutralizing antibody to MLO-Y4 cell conditioned medium. To study primary osteocytes, we prepared non-osteocytic cell-free osteocyte-enriched bone fragments (OEBFs). When osteoclast precursors were induced by macrophage colony-stimulating factor in the presence of OEBFs, the generated cells exhibited a diminished capacity for osteoclastogenesis. OEBFs prepared from OPG-knock-out mice exhibited a similar effect, indicating OPG-independent inhibition. The addition of anti-IFN-β neutralizing antibody during the co-culture with OEBFs partially recovered the osteoclastogenic potential of the generated cells. The MLO-Y4 cells and OEBFs expressed IFN-β mRNA. Although osteocytic RANKL is known to be important for osteoclastogenesis, our data suggest that osteocytes also produce IFN-β as an inhibitor of osteoclastogenesis.

Bone marrow plasma macrophage inflammatory protein protein-1 alpha(MIP-1 alpha) and sclerostin in multiple myeloma: relationship with bone disease and clinical characteristics

The aim of the study was to investigate the expression of MIP-1 alpha and sclerostin in bone marrow of patients with multiple myeloma (MM), the possible association of the sclerostin and MIP-1 alpha with MBD and the clinical characteristics. 53 patients (29 M, 24 F), median age 64 years was studied. MIP-1 alpha, sclerostin and bone-specific alkaline phosphatase (bALP) levels were quantified using an enzyme-linked immunosorbent assay (ELISA). Sclerostin and MIP-1 alpha mRNA expression was determined by RT-PCR. PTH and 1,25(OH) 2D3 levels were measured with an electrochemiluminescence immunoassay. The sclerostin and MIP-1 alpha concentrations in patients with MM were higher than those in the controls. RT-PCR analysis verified that the bone marrow mononuclear cells (BMMNCs) of most patients showed sclerostin and MIP-1 alpha mRNA expression. The sclerostin and MIP-1 alpha levels in patients with ISS stage III disease were significantly higher than those in patients with ISS stage II disease (p=0.01 and 0.06). The sclerostin and MIP-1 alpha levels in patients with BMD in group C were significantly higher than those in group A+B. There was positive correlation between sclerostin levels and MIP-1 alpha, beta2-microglobulin and aCa levels. A negative association was seen between sclerostin levels and bALP, HB and ALB levels. The MM patients with high sclerostin levels (>0.72 ng/ml) had significantly shorter median survival than those with low sclerostin levels (≤0.72 ng/ml) (χ(2)=7.574, p=0.006). Our findings support the positive relationship between sclerostin levels and MIP-1alpha levels deserve further detailed research.

Developments in sclerostin biology: regulation of gene expression, mechanisms of action, and physiological functions

The SOST gene, which encodes the protein sclerostin, was identified through genetic linkage analysis of sclerosteosis and van Buchem's disease patients. Sclerostin is a secreted glycoprotein that binds to the low-density lipoprotein receptor-related proteins 4, 5, and 6 to inhibit Wnt signaling. Since the initial discovery of sclerostin, much understanding has been gained into the role of this protein in the regulation of skeletal biology. In this article, we discuss the latest findings in the regulation of SOST expression, sclerostin mechanisms of action, and the potential utility of targeting sclerostin in conditions of low bone mass.

Relative influence of heritability, environment and genetics on serum sclerostin

SUMMARY

We determined factors associated with serum sclerostin in 446 Afro-Caribbean family members. Age, weight, sex, diabetes and kidney function were associated with sclerostin. Sclerostin was heritable, and nine SNPs in the SOST gene region were associated with sclerostin. Variation in serum sclerostin is a heritable factor that is determined by both genetic and environmental factors.

INTRODUCTION

Sclerostin, encoded by the SOST gene, is a Wnt inhibitor that regulates bone mineralization and is a candidate gene locus for osteoporosis. However, little is known about the genetic and non-genetic sources of inter-individual variation in serum sclerostin levels.

METHODS

Serum sclerostin was measured in 446 Afro-Caribbean men and women aged 18+ from seven large, multigenerational families (mean family size, 64; 3,840 relative pairs). Thirty-six common single nucleotide polymorphisms (SNP) were genotyped within a 100 kb region encompassing the gene encoding sclerostin (SOST). Genetic and non-genetic factors were tested for association with serum sclerostin.

RESULTS

Mean serum sclerostin was 41.3 pmol/l and was greater in men than in women (P < 0.05). Factors associated with higher serum sclerostin were increased age and body weight, male sex, diabetes and decreased glomerular filtration rate, which collectively accounted for 25.4 % of its variation. Residual genetic heritability of serum sclerostin was 0.393 (P < 0.0001). Nine SNPs reached nominal significance with sclerostin. Three of those nine SNPs represented independent association signals (rs851056, rs41455049 and rs9909172), which accounted for 7.8 % of the phenotypic variation in sclerostin, although none of these SNPs surpassed a Bonferroni correction for multiple comparisons.

CONCLUSIONS

Serum sclerostin is a heritable trait that is also determined by environmental factors including age, sex, adiposity, diabetes and kidney function. Three independent common SNPs within the SOST region may collectively account for a significant proportion of the variation in serum sclerostin.

Sclerostin serum levels in prostate cancer patients and their relationship with sex steroids

The role of sclerostin on bone metabolism and its relation to sex steroids in patients with prostate cancer (PC) is not well known. We found that sclerostin levels are significantly increased in PC patients, particularly in those with androgen deprivation therapy (ADT), and there is an inverse relationship between sclerostin levels and testosterone.

INTRODUCTION

Recent studies have evaluated sclerostin levels in bone diseases as osteoporosis. However, there are few data in PC patients, particularly in patients with hypogonadism related to ADT. The aim of the present study was to compare serum sclerostin levels in ADT/non-ADT-treated PC patients and healthy controls and to evaluate their relationship with sex steroids and bone metabolism.

METHODS

We performed a cross-sectional study involving 81 subjects: 25 ADT-treated PC patients, 34 PC patients without ADT treatment, and 22 healthy controls. We measured serum sclerostin levels, bone turnover markers, bone mineral density (BMD) in all individuals, and sex steroids levels in PC patients.

RESULTS

Serum sclerostin levels were significantly higher in PC patients compared to those in control subjects. ADT-treated patients had significantly higher sclerostin levels than PC patients without ADT treatment: ADT 64.52 ± 27.21 pmol/L, non-ADT 48.24 ± 15.93 pmol/L, healthy controls 38.48 ± 9.19 pmol/L, p < 0.05. In PC patients, we found a negative relationship between serum sclerostin levels and androgens after age adjustment (total testosterone: r = -0.309, p = 0.029; bioavailable testosterone: r = -0.280, p = 0.049; free testosterone: r = -0.299, p = 0.035). We did not observe any relationship between sclerostin levels and bone turnover markers or BMD in any group.

CONCLUSIONS

Circulating sclerostin levels are significantly increased in patients with PC and particularly in those receiving ADT. The inverse relationship between serum sclerostin and testosterone in these patients suggests that androgens are key regulators of bone metabolism in this population.

A brilliant breakthrough in OI type V

Interferon-induced transmembrane protein 5 or bone-restricted ifitm-like gene (Bril) was first identified as a bone gene in 2008, although no in vivo role was identified at that time. A role in human bone has now been demonstrated with a number of recent studies identifying a single point mutation in Bril as the causative mutation in osteogenesis imperfecta type V (OI type V). Such a discovery suggests a key role for Bril in skeletal regulation, and the completely novel nature of the gene raises the possibility of a new regulatory pathway in bone. Furthermore, the phenotype of OI type V has unique and quite divergent features compared with other forms of OI involving defects in collagen biology. Currently it appears that the underlying genetic defect in OI type V may be unrelated to collagen regulation, which also raises interesting questions about the classification of this form of OI. This review will discuss current knowledge of OI type V, the function of Bril, and the implications of this recent discovery.

Evaluation of the effects of systemic treatment with a sclerostin neutralizing antibody on bone repair in a rat femoral defect model

Systemic administration of a sclerostin neutralizing antibody (Scl-Ab) has been shown to enhance fracture callus density and strength in several animal models. In order to further evaluate the potential of Scl-Ab to improve healing in a bone defect model,we evaluated Scl-Ab in a 3mm femoral defect in young male outbred rats. Scl-Ab was given either continuously for 6 or 12 weeks after surgery or with 2 weeks of delay for 10 weeks. Bone formation was assessed by radiographs, µ-CT, and histology. Complete bony union was achieved in only a few defects after 12 weeks of healing (Scl-Ab treated 5/30, vehicle treated 1/15). µ-CT evaluation demonstrated a significant increase in the BV/TV in the defect in the delayed treatment group (65%, p<0.05), but a non-significant increase in the continuous group (35%, p = 0.11) compared to control. However, both regimens induced an anabolic response in the bone proximal and distal to the defect and in the un-operated femurs. We demonstrate that treatment with Scl-Ab can enhance bone repair in a bone defect and in the surrounding host bone, but lacks the osteoinductive activity to heal it. This agent seems to be most effective in bone repair scenarios where there is cortical integrity.

Serum sclerostin levels are decreased in adult patients with different types of osteogenesis imperfecta

CONTEXT

There are no specific biochemical bone markers available for osteogenesis imperfecta (OI), and the role of sclerostin as a key regulator of bone formation in OI is unknown.

OBJECTIVES

We aimed to evaluate the role of sclerostin and its association with bone turnover markers as well as body composition parameters in adult patients with different types of OI.

DESIGN, SETTING, AND PARTICIPANTS

This was a case-control study in 27 adult patients and 50 healthy age- and gender-matched controls.

MAIN OUTCOME MEASURES

Serum sclerostin levels and bone turnover markers including serum osteocalcin, amino terminal propeptide of type I procollagen, and CrossLaps as well as body composition parameters were determined in mild OI stage I (OI-I) and moderate-severe OI stages III-IV (OI-III-IV), according to Sillence classification. Data were compared with healthy controls.

RESULTS

Sclerostin levels were significantly lower in OI-I (19.9 ± 10.9 pmol/L; P < .001) and OI-III-IV (13.3 ± 10.0 pmol/L; P < .001) compared with healthy adults (45.3 ± 14.9 pmol/L), even after adjustment for age, sex, bone mineral content, and body mass index. CrossLaps and PTH were significantly lower in OI-I (0.197 ± 0.15 ng/L; P = .007 and 33.7 ± 19.1 pg/L; P = .033, respectively) and OI-III-IV (0.221 ± 0.18 ng/L; P = .039, and 27.9 ± 14.7 pg/L; P = .001, respectively) than in healthy controls (0.322 ± 0.15 ng/L and 45.0 ± 16.6 pg/L). Amino-terminal propeptide of type I procollagen was below the reference range for OI-I and OI-III-IV. Patients with OI were shorter and lighter and had a decreased bone mineral content (P < .001) but similar fat distribution and lean body mass, compared with controls. Serum sclerostin levels were not related to any bone marker except osteocalcin, the number of prevalent fractures, or body composition readings.

CONCLUSION

Decreased sclerostin levels in OI might reflect a down-regulation or negative feedback mechanism to prevent further bone loss.

The neurobiology of skeletal pain

Disorders of the skeleton are one of the most common causes of chronic pain and long-term physical disability in the world. Chronic skeletal pain is caused by a remarkably diverse group of conditions including trauma-induced fracture, osteoarthritis, osteoporosis, low back pain, orthopedic procedures, celiac disease, sickle cell disease and bone cancer. While these disorders are diverse, what they share in common is that when chronic skeletal pain occurs in these disorders, there are currently few therapies that can fully control the pain without significant unwanted side effects. In this review we focus on recent advances in our knowledge concerning the unique population of primary afferent sensory nerve fibers that innervate the skeleton, the nociceptive and neuropathic mechanisms that are involved in driving skeletal pain, and the neurochemical and structural changes that can occur in sensory and sympathetic nerve fibers and the CNS in chronic skeletal pain. We also discuss therapies targeting nerve growth factor or sclerostin for treating skeletal pain. These therapies have provided unique insight into the factors that drive skeletal pain and the structural decline that occurs in the aging skeleton. We conclude by discussing how these advances have changed our understanding and potentially the therapeutic options for treating and/or preventing chronic pain in the injured, diseased and aged skeleton.

Using Human Induced Pluripotent Stem Cells to Model Skeletal Diseases

Musculoskeletal disorders affecting the bones and joints are major health problems among children and adults. Major challenges such as the genetic origins or poor diagnostics of severe skeletal disease hinder our understanding of human skeletal diseases. The recent advent of human induced pluripotent stem cells (human iPS cells) provides an unparalleled opportunity to create human-specific models of human skeletal diseases. iPS cells have the ability to self-renew, allowing us to obtain large amounts of starting material, and have the potential to differentiate into any cell types in the body. In addition, they can carry one or more mutations responsible for the disease of interest or be genetically corrected to create isogenic controls. Our work has focused on modeling rare musculoskeletal disorders including fibrodysplasia ossificans progressive (FOP), a congenital disease of increased heterotopic ossification. In this review, we will discuss our experiences and protocols differentiating human iPS cells toward the osteogenic lineage and their application to model skeletal diseases. A number of critical challenges and exciting new approaches are also discussed, which will allow the skeletal biology field to harness the potential of human iPS cells as a critical model system for understanding diseases of abnormal skeletal formation and bone regeneration.

Circulating sclerostin and irisin are related and interact with gender to influence adiposity in adults with prediabetes

Objectives. Sclerostin, an osteocyte-specific protein, has been found to be related to adiposity and glucose metabolism. Irisin, a myokine, can affect browning of white fat and influence glucose and energy homeostasis. Taken together, this suggests a probable network among fat, bone, and muscle that may influence health outcomes. The aims of this study were to investigate the relationship of circulating sclerostin and irisin and their association with adiposity (assessed by body mass index (BMI)). Materials/Methods. A cross-sectional study included 98 adults with impaired fasting glucose and/or impaired glucose tolerance. 75 gm OGTT was performed in all subjects. Fasting plasma samples were obtained for glycated hemoglobin, calcium, creatinine, serum sclerostin and irisin. Results. Circulating irisin and sclerostin were highly correlated (r = -0.4; P < 0.001). After controlling for age, gender, and BMI, irisin was significantly related to sclerostin (P < 0.001). Multivariate linear regression analysis demonstrated that circulating sclerostin (β = -0.45; P < 0.05) and irisin (β = -0.46; P < 0.05) were negatively associated with BMI, independent of age in males. In females, no relationship of sclerostin or irisin to BMI was found. Conclusions. Circulating irisin and sclerostin are highly related. Interventions targeting irisin could affect sclerostin and vice versa.

Alkaptonuria

Alkaptonuria (AKU) is a rare disorder of autosomal recessive inheritance. It is caused by a mutation in a gene that results in the accumulation of homogentisic acid (HGA). Characteristically, the excess HGA means sufferers pass dark urine, which upon standing turns black. This is a feature present from birth. Over time patients develop other manifestations of AKU, due to deposition of HGA in collagenous tissues, namely ochronosis and ochronotic osteoarthropathy.   Although this condition does not reduce life expectancy, it significantly affects quality of life. The natural history of this condition is becoming better understood, despite gaps in knowledge. Clinical assessment of the condition has also improved along with the development of a potentially disease-modifying therapy. Furthermore, recent developments in AKU research have led to new understanding of the disease, and further study of the AKU arthropathy has the potential to influence therapy in the management of osteoarthritis.

Osteogenesis of heterotopically transplanted mesenchymal stromal cells in rat models of chronic kidney disease

The current study is based on the hypothesis of mesenchymal stromal cells (MSCs) contributing to soft-tissue calcification and ectopic osteogenesis in chronic kidney disease (CKD). Rat MSCs were transplanted intraperitoneally in an established three-dimensional collagen-based model in healthy control animals and two rat models of CKD and vascular calcification: (1) 5/6 nephrectomy + high phosphorus diet; and (2) adenine nephropathy. As internal controls, collagen gels without MSCs were transplanted in the same animals. After 4 and 8 weeks, MSCs were still detectable and proliferating in the collagen gels (fluorescence-activated cell sorting [FACS] analysis and confocal microscopy after fluorescence labeling of the cells). Aortas and MSC-containing collagen gels in CKD animals showed distinct similarities in calcification (micro-computed tomography [µCT], energy-dispersive X-ray [EDX] analysis, calcium content), induction of osteogenic markers, (ie, bone morphogenic protein 2 [BMP-2], Runt related transcription factor 2 [Runx2], alkaline phosphatase [ALP]), upregulation of the osteocytic marker sclerostin and extracellular matrix remodeling with increased expression of osteopontin, collagen I/III/IV, fibronectin, and laminin. Calcification, osteogenesis, and matrix remodeling were never observed in healthy control animals and non-MSC-containing collagen gels in all groups. Paul Karl Horan 26 (PKH-26)-labeled, 3G5-positive MSCs expressed Runx2 and sclerostin in CKD animals whereas PKH-26-negative migrated cells did not express osteogenic markers. In conclusion, heterotopically implanted MSCs undergo osteogenic differentiation in rat models of CKD-induced vascular calcification, supporting our hypothesis of MSCs as possible players in heterotopic calcification processes of CKD patients.

Role of sclerostin in the bone loss of postmenopausal chinese women with type 2 diabetes

OBJECTIVE

To evaluate the role of sclerostin in bone loss of postmenopausal Chinese women with type 2 diabetes mellitus.

METHODS

The postmenopausal patients suffering from type 2 diabetes mellitus and age, body mass index, and duration of menopause matched healthy controls were enrolled into this cross-sectional study according to criteria of inclusion and exclusion. The serum sclerostin level and bone mineral density of the anterior-posterior lumbar spine (L1-L4), femoral neck, and total hip were determined by using a quantitative sandwich ELISA kit and dual X-ray absorptiometry, respectively. Meanwhile, the clinical and laboratory indexes of bone mineral metabolism were analyzed. Associations between serum sclerostin level and bone mineral density as well as bone turnover markers were evaluated by linear regression analysis.

RESULTS

Finally, 265 postmenopausal women with type 2 diabetes and 225 non-diabetic women were recruited in the diabetic group and control group, respectively. Serum sclerostin level of the diabetic group was significantly higher than that of the control group (48.2±19.4 vs. 37.2±18.6 pmol/L, P<0.001) and was increased with age in both groups (diabetic group, r=0.374, P<0.001; control group, r=0.312, P<0.001). In type 2 diabetes patients, serum sclerostin concentration was positively correlated with hemoglobin A1c level (r=0.237; P=0.021). Biochemical bone turnover markers, intact parathyroid hormone and bone-specific alkaline phosphatase, were negatively associated with serum sclerostin level (r=-0.138, P=0.078 and r=-0.265, P<0.001). Conversely, the positive correlation between sclerostin and C-terminal cross-linking telopeptide of type I collagen was found in diabetic patients (r=0.354, P<0.001). Serum sclerostin levels of the diabetic group were positively correlated with bone mineral density of the lumbar spine, femoral neck, and total hip (r=0.324, 0.367, and 0.416, respectively; all P<0.001).

CONCLUSIONS

Sclerostin might participate in the pathogenesis of bone loss of type 2 diabetes. The high sclerostin level might serve as a marker of increased osteocyte activity in postmenopausal patients with type 2 diabetes mellitus.

Traditional and novel bone remodeling markers in premenopausal and postmenopausal women

CONTEXT

Bone turnover markers (BTMs) may identify changes in bone remodeling within a relatively short time interval before changes in bone mineral density can be detected. New markers such as osteoprotegerin, receptor activator of nuclear factor-κB ligand, and sclerostin have emerged, but there is little information about their potential use in clinical practice.

OBJECTIVES

The aim of this study was to analyze the ability of several BTMs to predict bone loss in pre- and postmenopausal women and to monitor the efficacy of treatment in osteoporotic women.

DESIGN, PATIENTS, AND SETTING

We performed an observational prospective study in pre- and postmenopausal ambulatory women (n = 72 and n = 152, respectively).

INTERVENTION

Postmenopausal women with osteoporosis (n = 18) were treated with risedronate and calcium. Women filled out a questionnaire and underwent bone mineral density measurement using dual-energy x-ray absorptiometry at the time of enrollment and after 1 year of follow-up. BTMs were measured at baseline, at 6 months, and after 1 year.

RESULTS

Increased levels of N-terminal propeptide of type 1 procollagen (P1NP) and β-type I collagen telopeptides (CTXs) were associated with low bone mineral density in the premenopausal (P = .02 and P = .04, respectively) and postmenopausal (P = .03 and P = .02) groups. The best analytical performance to diagnose osteoporosis was for β-CTX, osteocalcin, and P1NP, with areas under the curve of 0.70 (P = .005), 0.64 (P = .048), and 0.71 (P = .003). A significant decrease was found in P1NP, osteocalcin, tartrate-resistant acid phosphatase-5b, β-CTX, and bone alkaline phosphatase after 1 year of treatment (all P < .05).

CONCLUSIONS

Our data suggest that measurement of β-CTX and P1NP shows adequate analytical performance and could potentially be included in algorithms for the screening of osteoporosis. Furthermore, these two markers, along with osteocalcin and tartrate-resistant acid phosphatase-5b, are useful to monitor the response to risedronate.

Connexin 43 deficiency desensitizes bone to the effects of mechanical unloading through modulation of both arms of bone remodeling

Connexin 43 (Cx43) is a gap junction protein that plays an integral role in the skeletal response to mechanical loading and unloading. In a previous study, we demonstrated preservation of trabecular bone mass and cortical bone formation rate in mice with an osteoblast/osteocyte-selective deficiency of Cx43 (cKO) following mechanical unloading via hindlimb suspension (HLS). In the present study, we sought to define the potential mechanisms underlying this response. Following three weeks of HLS, mRNA levels of Sost were significantly greater in wild-type (WT)-Suspended mice vs. WT-Control, while there was no difference between cKO control and cKO-Suspended. Unloading-induced decreases in P1NP, a serum marker of bone formation, were also attenuated in cKO-Suspended. The proportion of sclerostin-positive osteocytes was significantly lower in cKO-Control vs. WT-Control (-72%, p<0.05), a difference accounted for by the presence of numerous empty lacunae in the cortical bone of cKO vs. WT. Abundant TUNEL staining was present throughout the cortical bone of the tibia and femur, suggesting an apoptotic process. There was no difference in empty lacunae in the trabecular bone of the tibia or femur. Trabecular and cortical osteoclast indices were lower in cKO-Suspended vs. WT-Suspended; however, mRNA levels of the gene encoding RANKL increased similarly in both genotypes. Connexin 43 deficient mice experience attenuated sclerostin-mediated suppression of cortical bone formation and lower cortical osteoclast activity during unloading. Preservation of trabecular bone mass and attenuated osteoclast activity during unloading, despite an apparent lack of effect on osteocyte viability at this site, suggests that an additional mechanism independent of osteocyte apoptosis may also be important. These findings indicate that Cx43 is able to modulate both arms of bone remodeling during unloading.

Genetic association study of Dickkopf-1 and sclerostin genes with paget disease of bone

Increased expression of DKK1 gene was reported in pagetic osteoblasts and stromal cells, and increased serum levels of DKK1 and SOST proteins were reported in patients with Paget disease of bone (PDB). This study aimed at identifying rare genetic variants of the DKK1 and SOST genes and at testing for genetic association with PDB in the French-Canadian population. Exons, promoters, and exon-intron junctions of these genes were sequenced in patients with PDB and healthy controls. An association study of Tag SNPs of both genes was also performed in 239 pagetic patients and 297 healthy individuals. Three rare variants were identified in this study, all located in the DKK1 gene: one variant in the second exon leading to alteration in a highly conserved amino acid (p.R120L), one in the 5'-untranslated region (-50 C/A), and one in a splice site of intron 1 (IVS1 184 T/C), although none of these rare variants were associated with PDB. A genetic association of a Tag SNP of the DKK1 gene was found: the G allele of rs1569198 was significantly decreased in patients in comparison to controls (42 vs. 49 %, uncorrected P = 0.03, OR = 0.77, 95 % CI 0.61-0.98). In conclusion, this study identified three rare genetic variants in DKK1 in the French-Canadian population. In addition, a weak genetic association of a common variant of DKK1, rs1569198, which is located on a predicted new acceptor site for splicing of this gene, was observed in PDB, whereas no rare variant or genetic association was found in the SOST gene.

The effect on proliferation and differentiation of cementoblast by using sclerostin as inhibitor

Cementogenesis is of great importance for normal teeth root development and is involved in the repair process of root resorption caused by orthodontic treatment. As highly differentiated mesenchymal cells, cementoblasts are responsible for this process under the regulation of many endogenous agents. Among these molecules, sclerostin has been much investigated recently for its distinct antagonism effect on bone metabolism. Encoded by the sost gene, sclerostin is expressed in osteocytes and cementocytes of cellular cementum. it is still unclear. In the current study, we investigated the effects of sclerostin on the processes of proliferation and differentiation; a series of experiments including MTT, apoptosis examination, alkaline phosphatase (ALP) activity, gene analysis, and alizarin red staining were carried out to evaluate the proliferation and differentiation of cementoblasts. Protein expression including osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) were also checked to analyze changes in osteoclastogenesis. Results show that sclerostin inhibits cementoblasts proliferation and differentiation, and promotes osteoclastogenesis. Interestingly, the monoclonal antibody for sclerostin has shown positive effects on osteoporosis, indicating that it may facilitate cementogenesis and benefit the treatment of cementum related diseases.

Relationship between sclerostin and cardiovascular calcification in hemodialysis patients: a cross-sectional study

Background

Sclerostin is a Wnt pathway antagonist regulating osteoblast activity and bone turnover. Here, we assessed the potential association of sclerostin with the development of coronary artery (CAC) and aortic valve calcifications (AVC) in haemodialysis (HD) patients.

Methods

We conducted a cross-sectional multi-slice computed tomography (MS-CT) scanning study in 67 chronic HD patients (59.4 ± 14.8 yrs) for measurement of CAC and AVC. We tested established biomarkers as well as serum sclerostin (ELISA) regarding their association to the presence of calcification. Fifty-four adults without relevant renal disease served as controls for serum sclerostin levels. Additionally, sclerostin expression in explanted aortic valves from 15 dialysis patients was analysed ex vivo by immunohistochemistry and mRNA quantification (Qt-RT-PCR).

Results

CAC (Agatston score > 100) and any AVC were present in 65% and in 40% of the MS-CT patient group, respectively. Serum sclerostin levels (1.53 ± 0.81 vs 0.76 ± 0.31 ng/mL, p < 0.001) were significantly elevated in HD compared to controls and more so in HD patients with AVC versus those without AVC (1.78 ± 0.84 vs 1.35 ± 0.73 ng/mL, p = 0.02). Multivariable regression analysis for AVC revealed significant associations with higher serum sclerostin. Ex vivo analysis of uraemic calcified aortic valves (n = 10) revealed a strong sclerostin expression very close to calcified regions (no sclerostin staining in non-calcified valves). Correspondingly, we observed a highly significant upregulation of sclerostin mRNA in calcified valves compared to non-calcified control valves.

Conclusion

We found a strong association of sclerostin with calcifying aortic heart valve disease in haemodialysis patients. Sclerostin is locally produced in aortic valve tissue adjacent to areas of calcification.

Metabolic and endocrine diseases, cartilage calcification and arthritis

PURPOSE OF REVIEW

Osteoarthritis is the most common form of rheumatologic disease, with numerous factors increasing the risk of developing the condition; calcification of cartilage is common place in osteoarthritis. Regardless of these risk factors, certain disorders predispose individuals to developing arthritis. Pathologic mechanisms in cartilage calcification and advances in their understanding are reviewed alongside metabolic and endocrine arthritis.

RECENT FINDINGS

There is growing evidence suggesting that changes in chondrocytes and the extracellular environment both contribute to the calcification. Further evidence suggests that signaling cascades that are involved in physiological mineralisation are involved in the pathological process(es); data in mouse models continue to add weight to these hypotheses and correlate with human osteoarthritis data. Recent study of rare forms of arthritis is adding useful information that may help understand joint diseases in the general population and how therapies may be targeted.

SUMMARY

There is little doubt that calcium-containing crystals are involved in the osteoarthritis process contributing both biomechanically and biochemically. Understanding the processes involved provides important therapeutic opportunities. Furthermore, important information is often discovered in studying rare conditions in which these pathologies are inevitable.

Pathobiology and management of prostate cancer-induced bone pain: recent insights and future treatments

Prostate cancer (PCa) has a high propensity for metastasis to bone. Despite the availability of multiple treatment options for relief of PCa-induced bone pain (PCIBP), satisfactory relief of intractable pain in patients with advanced bony metastases is challenging for the clinicians because currently available analgesic drugs are often limited by poor efficacy and/or dose-limiting side effects. Rodent models developed in the past decade show that the pathobiology of PCIBP comprises elements of inflammatory, neuropathic and ischemic pain arising from ectopic sprouting and sensitization of sensory nerve fibres within PCa-invaded bones. In addition, at the cellular level, PCIBP is underpinned by dynamic cross talk between metastatic PCa cells, cellular components of the bone matrix, factors associated with the bone microenvironment as well as peripheral components of the somatosensory system. These insights are aligned with the clinical management of PCIBP involving use of a multimodal treatment approach comprising analgesic agents (opioids, NSAIDs), radiotherapy, radioisotopes, cancer chemotherapy agents and bisphosphonates. However, a major drawback of most rodent models of PCIBP is their short-term applicability due to ethical concerns. Thus, it has been difficult to gain insight into the mal(adaptive) neuroplastic changes occurring at multiple levels of the somatosensory system that likely contribute to intractable pain at the advanced stages of metastatic disease. Specifically, the functional responsiveness of noxious circuitry as well as the neurochemical signature of a broad array of pro-hyperalgesic mediators in the dorsal root ganglia and spinal cord of rodent models of PCIBP is relatively poorly characterized. Hence, recent work from our laboratory to develop a protocol for an optimized rat model of PCIBP will enable these knowledge gaps to be addressed as well as identification of novel targets for drug discovery programs aimed at producing new analgesics for the improved relief of intractable PCIBP.

Involvement of WNT/β-catenin signaling in the treatment of osteoporosis

Osteoblast differentiation is predominantly regulated by the WNT/β-catenin signaling (canonical WNT pathway), which, together with bone morphogenetic proteins, acts as the master regulator of osteogenesis. The recent characterization of the canonical WNT pathway in the regulation of bone modeling and remodeling provided important insights for our understanding of the pathophysiology of a number of conditions and of the mechanism of action of hormones or drugs with important effect on bone metabolism. This review is mainly focused on the growing therapeutic implications of these new findings. WNT/β-catenin signaling plays a key role in bone tissue by determining the differentiation of stem cells into mature osteoblasts rather than into chondrocytes and adipocytes. Its regulation is predominantly driven by the production of two WNT signaling antagonists: sclerostin (SOST) and Dickkopf-related protein 1 (DKK1). The most proximate regulator of SOST expression by osteocytes and its serum levels is bone mechanical load. SOST expression is increased with advancing age, by glucocorticoid treatment and during treatment with antiresorptive agents such as bisphosphonates and denosumab, while it is decreased by parathyroid hormone excess or administration of estrogens. Correlation between DKK1 serum levels and bone formation in various pathological conditions or during osteoporosis treatment has been reported. Inhibitors of the negative regulators of WNT/β-catenin signaling ("inhibiting the endogenous inhibitors") are potential candidates for the prevention and treatment of bone loss. Inactivating monoclonal antibodies against SOST appears to be the most attractive strategy because SOST is the only component of the WNT pathway expressed almost exclusively by osteocytes.

Correlates of bone microarchitectural parameters and serum sclerostin levels in men: the STRAMBO study

Sclerostin is predominantly expressed by osteocytes. Serum sclerostin levels are positively correlated with areal bone mineral density (aBMD) measured by dual-energy X-ray absorptiometry (DXA) and bone microarchitecture assessed by high-resolution peripheral quantitative computed tomography (HR-pQCT) in small studies. We assessed the relation of serum sclerostin levels with aBMD and microarchitectural parameters based on HR-pQCT in 1134 men aged 20 to 87 years using multivariable models adjusted for confounders (age, body size, lifestyle, comorbidities, hormones regulating bone metabolism, muscle mass and strength). The apparent age-related increase in serum sclerostin levels was faster before the age of 63 years than afterward (0.43 SD versus 0.20 SD per decade). In 446 men aged ≤63 years, aBMD (spine, hip, whole body), trabecular volumetric BMD (Tb.vBMD), and trabecular number (Tb.N) at the distal radius and tibia were higher in the highest sclerostin quartile versus the three lower quartiles combined. After adjustment for aBMD, men in the highest sclerostin quartile had higher Tb.vBMD (mainly in the central compartment) and Tb.N at both skeletal sites (p < 0.05 to 0.001). In 688 men aged >63 years, aBMD was positively associated with serum sclerostin levels at all skeletal sites. Cortical vBMD (Ct.vBMD) and cortical thickness (Ct.Th) were lower in the first sclerostin quartile versus the three higher quartiles combined. Tb.vBMD increased across the sclerostin quartiles, and was associated with lower Tb.N and more heterogeneous trabecular distribution (higher Tb.Sp.SD) in men in the lowest sclerostin quartile. After adjustment for aBMD, men in the lowest sclerostin quartile had lower Tb.vBMD and Tb.N, but higher Tb.Sp.SD (p < 0.05 to 0.001) at both the skeletal sites. In conclusion, serum sclerostin levels in men are strongly positively associated with better bone microarchitectural parameters, mainly trabecular architecture, regardless of the potential confounders.

Is interaction between age-dependent decline in mechanical stimulation and osteocyte-estrogen receptor levels the culprit for postmenopausal-impaired bone formation?

Declining estrogen levels during menopause are widely considered to be a major cause of age-dependent bone loss, which is primarily manifested by increased bone resorption by osteoclasts. We present accumulating evidence supporting another aspect of metabolic bone loss, suggesting that the combined interaction between age-dependent factors, namely, estrogen deficiency and reduced day-by-day activity/mechanical stimulation, directly leads to a reduction in anabolic processes. Such decreased bone formation results in diminished bone strength and failure to maintain the load-bearing competence of a healthy skeleton and to postmenopausal osteoporosis disorder. Estrogen receptors (ERs), as mediators of estrogenic actions, are essential components of bone osteocyte and osteoblast mechano-adaptive responses. ER expression appears to be upregulated by adequate circulating estrogen levels. ERα signaling pathways participate in the mechanotransduction response through obligatory "non-genomic" actions that occur independently of estrogen binding to ER and by a potentially "genomic", estrogen-dependent mode. The experimental data indicate that cross talk between the ERα-"non-genomic" and Wnt/β-catenin signaling pathways constitutes the major regulatory mechanism. This interaction uses mechanically and ER-induced prostaglandin E2 as a mediator for the downregulation of osteocyte production of sclerostin. Sclerostin suppression, in turn, is a central prerequisite for load-induced formation and mineralization of the bone matrix. It is therefore plausible that future strategies for preventing and treating postmenopausal osteoporosis may use estrogenic compounds (such as selective estrogen receptor modulators or phytoestrogens) with physical activity, to complement antiresorptive therapy, aimed at stopping further bone loss and possibly even reversing it by stimulation of bone gain.

Sclerostin: A Novel Player Regulating Bone Mass in Inflammation?

Inflammation is a common albeit overlooked cause of local and systemic bone loss which results from an imbalance between bone formation and bone resorption. The Wnt pathway, which plays an essential role in the regulation of bone turnover, has been proposed as a potential molecular link between inflammation and inflammatory bone loss. We here recapitulate present knowledge about sclerostin, a Wnt pathway inhibitor, and bone damage in inflammation. A better understanding of sclerostin action and regulation might help in designing an effective treatment strategy in inflammatory bone loss.

RUNX2 in mammary gland development and breast cancer

Runx2 is best known as an essential factor in osteoblast differentiation and bone development but, like many other transcription factors involved in development, is known to operate over a much wider tissue range. Our understanding of these other aspects of Runx2 function is still at a relatively early stage and the importance of its role in cell fate decisions and lineage maintenance in non-osseous tissues is only beginning to emerge. One such tissue is the mammary gland, where Runx2 is known to be expressed and participate in the regulation of mammary specific genes. Furthermore, differential and temporal expression of this gene is observed during mammary epithelial differentiation in vivo, strongly indicative of an important functional role. Although the precise nature of that role remains elusive, preliminary evidence hints at possible involvement in the regulation of mammary stem and/or progenitor cells. As with many genes important in regulating cell fate, RUNX2 has also been linked to metastatic cancer where in some established breast cell lines, retention of expression is associated with a more invasive phenotype. More recently, expression analysis has been extended to primary breast cancers where high levels of RUNX2 align with a specific subtype of the disease. That RUNX2 expression correlates with the so called "Triple Negative" subtype is particularly interesting given the known cross talk between Runx2 and estrogen receptor signaling pathways. This review summaries our current understanding of Runx2 in mammary gland development and cancer, and postulates a role that may link both these processes.

Low bone turnover and low bone density in a cohort of adults with Down syndrome

Increased incidence of osteoporosis in Down syndrome has been reported, but etiology is not established. We report low bone turnover markers and bone mineral density (BMD) in a cohort of people with Down syndrome without consistent clinical risk factors. Our results should guide future studies and treatments for this common problem.

INTRODUCTION

To better understand the etiology for osteoporosis in Down syndrome (DS), we measured bone density by dual-energy X-ray absorptiometry (DXA) and circulating biochemical markers of bone formation and resorption in a cohort of 30 community-dwelling DS adults.

METHODS

Seventeen males and 13 females followed in the University of Arkansas Down Syndrome Clinic were evaluated by DXA to estimate BMD and underwent phlebotomy to measure serum procollagen type-1 intact N-terminal propeptide (P1NP) to evaluate bone formation, and serum C-terminal peptide of type-I collagen (CTx) to evaluate bone resorption.

RESULTS

Seven of 13 DS females and 12 of 17 DS males had low bone mass at one of measured sites (z≤-2.0). When data were grouped by age, males had apparent osteopenia earlier than females. The mean P1NP in the normal group was 19.2±5.2 ng/ml vs. 2.2±0.9 ng/ml in the DS group (P=0.002). Serum CTx levels in the normal group were 0.4±0.1 ng/ml vs. 0.3±0.1 ng/ml (P=0.369).

CONCLUSIONS

Low BMD in adults with DS is correlated with a significant decrease in bone formation markers, compared to controls without DS, and is independent of gender. These data suggest that diminished osteoblastic bone formation and inadequate accrual of bone mass, with no significant differences in bone resorption, are responsible for the low bone mass in DS. These observations question the use of antiresorptive therapy in this population and focus attention on increasing bone mass by other interventions.