Alternated activation with relaxation of periosteum stimulates bone modeling and remodeling

Gradual elevation of the periosteum from the original bone surface, based on the principle of distraction osteogenesis, induces endogenous hard and soft tissue formation. This study aimed to assess the impact of alternating protocols of activation with relaxation (periosteal pumping) on bone modeling and remodeling. One hundred and sixty-two adult male Wistar rats were used in this study. Four test groups with different pumping protocols were created based on the relaxation applied. Two control groups underwent an activation period without relaxation or only a single activation. One group was sham-operated. Periosteal pumping without period of activation induced gene expression in bone and bone remodeling, and following activation period enhanced bone modeling. Four test groups and control group with activation period equaled the values of bone modeling at the end-consolidation period, showing significant downregulation of Sost in the bone and periosteum compared to that in the sham group (p < 0.001 and p < 0.001, respectively). When all test groups were pooled together, plate elevation from the bony surface increased bone remodeling on day 45 of the observation period (p = 0.003). Furthermore, bone modeling was significantly affected by plate elevation on days 17 and 45 (p = 0.047 and p = 0.005, respectively) and by pumping protocol on day 31 (p = 0.042). Periosteal pumping was beneficial for increasing bone repair when the periosteum remained in contact with the underlaying bony surface during the manipulation period. Following periosteal elevation, periosteal pumping accelerated bone formation from the bony surface by the modeling process.

The effects of time-restricted eating and weight loss on bone metabolism and health: a 6-month randomized controlled trial

OBJECTIVE

This study explored the impact of time-restricted eating (TRE) versus standard dietary advice (SDA) on bone health.

METHODS

Adults with ≥1 component of metabolic syndrome were randomized to TRE (ad libitum eating within 12 hours) or SDA (food pyramid brochure). Bone turnover markers and bone mineral content/density by dual energy x-ray absorptiometry were assessed at baseline and 6-month follow-up. Statistical analyses were performed in the total population and by weight loss response.

RESULTS

In the total population (n = 42, 76% women, median age 47 years [IQR: 31-52]), there were no between-group differences (TRE vs. SDA) in any bone parameter. Among weight loss responders (≥0.6 kg weight loss), the bone resorption marker β-carboxyterminal telopeptide of type I collagen tended to decrease after TRE but increase after SDA (between-group differences p = 0.041), whereas changes in the bone formation marker procollagen type I N-propeptide did not differ between groups. Total body bone mineral content decreased after SDA (p = 0.028) but remained unchanged after TRE (p = 0.31) in weight loss responders (between-group differences p = 0.028). Among nonresponders (<0.6 kg weight loss), there were no between-group differences in bone outcomes.

CONCLUSIONS

TRE had no detrimental impact on bone health, whereas, when weight loss occurred, it was associated with some bone-sparing effects compared with SDA.

Reference microarchitectural values measured by HR-pQCT in a Franco-Swiss cohort of young adult women

Bone microarchitecture assessed by high-resolution peripheral quantitative computed tomography varies across populations of different origin. The study presents a reference dataset of microarchitectural parameters in a homogeneous group of participants aged within 22-27 range determined by a discriminant analysis of a larger cross-sectional cohort of 339 women.

INTRODUCTION

High-resolution peripheral quantitative computed tomography (HR-pQCT) non-invasively measures three-dimensional bone microarchitectural parameters and volumetric bone mineral density. Previous studies established normative reference HR-pQCT datasets for several populations, but there were few data assessed in a reference group of young women with Caucasian ethnicity living in Western Europe. It is important to obtain different specific reference dataset for a valid interpretation of cortical and trabecular microarchitecture data. The aim of our study was to find the population with the most optimal bone status in order to establish a descriptive reference HR-pQCT dataset in a young and healthy normal-weight female cohort living in a European area including Geneva, Switzerland, Lyon and Saint-Etienne, France.

METHODS

We constituted a cross-sectional cohort of 339 women aged 19-41 years with a BMI > 18 and < 30 kg/m². All participants had HR-pQCT measurements at both non-dominant distal radius and tibia sites.

RESULTS

We observed that microarchitectural parameters begin to decline before the age of 30 years. Based on a discriminant analysis, the optimal bone profile in this population was observed between the age range of 22 to 27 years. Consequently, we considered 43 participants aged 22-27 years to establish a reference dataset with median values and percentiles.

CONCLUSION

This is the first study providing reference values of HR-pQCT measurements considering specific age bounds in a Franco-Swiss female cohort at the distal radius and tibia sites.

Regeneration of Craniofacial Bone Induced by Periosteal Pumping

A variety of surgical techniques and tissue engineering strategies utilizing osteogenic potential of the periosteum have been developed for the repair of extended bone deficiencies. The aim of the present study was to assess the impact of an alternating protocol of periosteal distraction osteogenesis (PDO) on bone regeneration in an intraoral model. Eight adult, male Beagle dogs were used for the study. Two distraction devices were placed on each side of the mandible. After a 7-day latency period, distraction devices in all animals were manipulated at the rate of 0.5 mm for a total of 8 days. The pumping protocol in two test groups proceeded twice daily by alternating activation with relaxation. In the periosteal pumping/distraction (PPDO) group, the distraction screws were activated two times (at 12 and 24 h) and then turned back (at 36 h), and in the periosteal pumping (PP) group repeatedly activated and turned back (at 12 h). In the PDO group, only activation was performed once daily (positive control). Devices were left inactivated in the negative control (NC) group. The samples were harvested after 8 weeks of consolidation period and investigated by micro-CT and histological analysis. New mature, lamellar bone was formed over the pristine bone in all groups. PPDO and PDO groups showed more new bone area (NBA) compared to the PP (p < 0.001 and p < 0.001, respectively) and to the NC group (p = 0.032 and p = 0.031, respectively). Furthermore, greater NBA was found in the PP group than the NC group (p = 0.006). PDO demonstrated higher relative connective tissue area than the PPDO group (p = 0.005) and lower relative new bone volume than the NC group (p = 0.025). Pumping protocol of periosteal distraction may successfully induce the endogenous regeneration of the mandibular bone in dogs. Impact Statement Repair of extended bone defects impose a significant challenge to oral and maxillofacial surgeons. In this article, a principle of distraction osteogenesis was applied to stimulate bone regeneration in the mandible. A periosteum-based regeneration approach may represent a valuable step toward creating a significant volume of hard and soft tissues, without need for autogenous bone harvesting or application of biomaterials.

Pathophysiology of Vascular Calcification and Bone Loss: Linked Disorders of Ageing?

Vascular Calcification (VC), low bone mass and fragility fractures are frequently observed in ageing subjects. Although this clinical observation could be the mere coincidence of frequent age-dependent disorders, clinical and experimental data suggest that VC and bone loss could share pathophysiological mechanisms. Indeed, VC is an active process of calcium and phosphate precipitation that involves the transition of the vascular smooth muscle cells (VSMCs) into osteoblast-like cells. Among the molecules involved in this process, parathyroid hormone (PTH) plays a key role acting through several mechanisms which includes the regulation of the RANK/RANKL/OPG system and the Wnt/ß-catenin pathway, the main pathways for bone resorption and bone formation, respectively. Furthermore, some microRNAs have been implicated as common regulators of bone metabolism, VC, left ventricle hypertrophy and myocardial fibrosis. Elucidating the common mechanisms between ageing; VC and bone loss could help to better understand the potential effects of osteoporosis drugs on the CV system.

Perspectives on the non-invasive evaluation of femoral strength in the assessment of hip fracture risk

We reviewed the experimental and clinical evidence that hip bone strength estimated by BMD and/or finite element analysis (FEA) reflects the actual strength of the proximal femur and is associated with hip fracture risk and its changes upon treatment.

INTRODUCTION

The risk of hip fractures increases exponentially with age due to a progressive loss of bone mass, deterioration of bone structure, and increased incidence of falls. Areal bone mineral density (aBMD), measured by dual-energy X-ray absorptiometry (DXA), is the most used surrogate marker of bone strength. However, age-related declines in bone strength exceed those of aBMD, and the majority of fractures occur in those who are not identified as osteoporotic by BMD testing. With hip fracture incidence increasing worldwide, the development of accurate methods to estimate bone strength in vivo would be very useful to predict the risk of hip fracture and to monitor the effects of osteoporosis therapies.

METHODS

We reviewed experimental and clinical evidence regarding the association between aBMD and/orCT-finite element analysis (FEA) estimated femoral strength and hip fracture risk as well as their changes with treatment.

RESULTS

Femoral aBMD and bone strength estimates by CT-FEA explain a large proportion of femoral strength ex vivo and predict hip fracture risk in vivo. Changes in femoral aBMD are strongly associated with anti-fracture efficacy of osteoporosis treatments, though comparable data for FEA are currently not available.

CONCLUSIONS

Hip aBMD and estimated femoral strength are good predictors of fracture risk and could potentially be used as surrogate endpoints for fracture in clinical trials. Further improvements of FEA may be achieved by incorporating trabecular orientations, enhanced cortical modeling, effects of aging on bone tissue ductility, and multiple sideway fall loading conditions.

Diagnosis and management of bone fragility in diabetes: an emerging challenge

Fragility fractures are increasingly recognized as a complication of both type 1 and type 2 diabetes, with fracture risk that increases with disease duration and poor glycemic control. Yet the identification and management of fracture risk in these patients remains challenging. This review explores the clinical characteristics of bone fragility in adults with diabetes and highlights recent studies that have evaluated bone mineral density (BMD), bone microstructure and material properties, biochemical markers, and fracture prediction algorithms (i.e., FRAX) in these patients. It further reviews the impact of diabetes drugs on bone as well as the efficacy of osteoporosis treatments in this population. We finally propose an algorithm for the identification and management of diabetic patients at increased fracture risk.

β-Klotho deficiency shifts the gut-liver bile acid axis and induces hepatic alterations in mice

β-Klotho (encoded by Klb) is an obligate coreceptor, mediating both fibroblast growth factor (FGF)15 and FGF21 signaling. Klb^-/- mice are refractory to metabolic FGF15 and FGF21 action and exhibit derepressed (increased) bile acid (BA) synthesis. Here, we deeply phenotyped male Klb^-/- mice on a pure C57BL/6J genetic background, fed a chow diet focusing on metabolic aspects. This aims to better understand the physiological consequences of concomitant FGF15 and FGF21 signaling deficiency, in particular on the gut-liver axis. Klb^-/- mice present permanent growth restriction independent of adiposity and energy balance. Klb^-/- mice also exhibit few changes in carbohydrate metabolism, combining normal gluco-tolerance, insulin sensitivity, and fasting response with increased gluconeogenic capacity and decreased glycogen mobilization. Livers of Klb^-/- mice reveal pathologic features, including a proinflammatory status and initiation of fibrosis. These defects are associated to a massive shift in BA composition in the enterohepatic system and blood circulation featured by a large excess of microbiota-derived deoxycholic acid, classically known for its genotoxicity in the gastrointestinal tract. In conclusion, β-Klotho is a gatekeeper of hepatic integrity through direct action (mediating FGF21 anti-inflammatory signaling) and indirect mechanisms (mediating FGF15 signaling that maintains BA level and composition).

Fermented dairy products consumption is associated with attenuated cortical bone loss independently of total calcium, protein, and energy intakes in healthy postmenopausal women

A longitudinal analysis of bone microstructure in postmenopausal women of the Geneva Retirees Cohort indicates that age-related cortical bone loss is attenuated at non-bearing bone sites in fermented dairy products consumers, not in milk or ripened cheese consumers, independently of total energy, calcium, or protein intakes.

INTRODUCTION

Fermented dairy products (FDP), including yogurts, provide calcium, phosphorus, and proteins together with prebiotics and probiotics, all being potentially beneficial for bone. In this prospective cohort study, we investigated whether FDP, milk, or ripened cheese consumptions influence age-related changes of bone mineral density (BMD) and microstructure.

METHODS

Dietary intakes were assessed at baseline and after 3.0 ± 0.5 years with a food frequency questionnaire in 482 postmenopausal women enrolled in the Geneva Retirees Cohort. Cortical (Ct) and trabecular (Tb) volumetric (v) BMD and microstructure at the distal radius and tibia were assessed by high-resolution peripheral quantitative computerized tomography, in addition to areal (a) BMD and body composition by dual-energy X-ray absorptiometry, at the same time points.

RESULTS

At baseline, FDP consumers had lower abdominal fat mass and larger bone size at the radius and tibia. Parathyroid hormone and β-carboxyterminal cross-linked telopeptide of type I collagen levels were inversely correlated with FDP consumption. In the longitudinal analysis, FDP consumption (mean of the two assessments) was associated with attenuated loss of radius total vBMD and of Ct vBMD, area, and thickness. There was no difference in aBMD and at the tibia. These associations were independent of total energy, calcium, or protein intakes. For other dairy products categories, only milk consumption was associated with lower decrease of aBMD and of failure load at the radius.

CONCLUSION

In this prospective cohort of healthy postmenopausal women, age-related Ct bone loss was attenuated at non-bearing bone sites in FDP consumers, not in milk or ripened cheese consumers, independently of total energy, calcium, or protein intakes.

STUDY REGISTRATION

ISRCTN11865958 ( http://www.isrctn.com ).

Interaction between LRP5 and periostin gene polymorphisms on serum periostin levels and cortical bone microstructure

We investigated the interaction between periostin SNPs and the SNPs of the genes assumed to modulate serum periostin levels and bone microstructure in a cohort of postmenopausal women. We identified an interaction between LRP5 SNP rs648438 and periostin SNP rs9547970 on serum periostin levels and on radial cortical porosity.

PURPOSE

The purpose of this study is to investigate the interaction between periostin gene polymorphisms (SNPs) and other genes potentially responsible for modulating serum periostin levels and bone microstructure in a cohort of postmenopausal women.

METHODS

In 648 postmenopausal women from the Geneva Retirees Cohort, we analyzed 6 periostin SNPs and another 149 SNPs in 14 genes, namely BMP2, CTNNB1, ESR1, ESR2, LRP5, LRP6, PTH, SPTBN1, SOST, TGFb1, TNFRSF11A, TNFSF11, TNFRSF11B and WNT16. Volumetric BMD and bone microstructure were measured by high-resolution peripheral quantitative computed tomography at the distal radius and tibia.

RESULTS

Serum periostin levels were associated with radial cortical porosity, including after adjustment for age, BMI, and years since menopause (p = 0.036). Sixteen SNPs in the ESR1, LRP5, TNFRSF11A, SOST, SPTBN1, TNFRSF11B and TNFSF11 genes were associated with serum periostin levels (p range 0.03-0.001) whereas 26 SNPs in 9 genes were associated with cortical porosity at the radius and/or at the tibia. WNT 16 was the gene with the highest number of SNPs associated with both trabecular and cortical microstructure. The periostin SNP rs9547970 was also associated with cortical porosity (p = 0.04). In particular, SNPs in LRP5, ESR1 and near the TNFRSF11A gene were associated with both cortical porosity and serum periostin levels. Eventually, we identified an interaction between LRP5 SNP rs648438 and periostin SNP rs9547970 on serum periostin levels (interaction p = 0.01) and on radial cortical porosity (interaction p = 0.005).

CONCLUSION

These results suggest that periostin expression is genetically modulated, particularly by polymorphisms in the Wnt pathway, and is thereby implicated in the genetic variation of bone microstructure.

Development of a New Immunoassay for Human Cathepsin K-Generated Periostin Fragments as a Serum Biomarker for Cortical Bone

Periostin is a matricellular protein mainly expressed by periosteal cells and osteocytes in bone, but is also present in several other tissues. Available immunoassays use antibodies of unclear specificity. The aim of the study was to develop a bone-specific periostin ELISA based on the detection of fragments generated by the osteoclastic and osteocytic protease cathepsin K. In vitro digestion of human recombinant intact periostin by cathepsin K leads to the generation of multiple fragments. Using LS-MS/MS, it was found that the GSLQPIIK peptide was the most efficiently and abundantly generated periostin fragment. A rabbit polyclonal antibody directed against the synthetic GSLQPIIK sequence was produced. Immunohistochemistry experiments of the tibia showed that the GSLQPIIK fragments localized at the periosteal surface and within the osteocytes. Using the same antibody, we developed an ELISA for the measurement of GSLQPIIK in the serum. This ELISA demonstrated intra- and interassay variability below 14% with a sensitivity allowing accurate determinations in the serum of healthy individuals. Serum GSLQPIIK was measured in 160 healthy postmenopausal women (mean age 65 year) participating in the Geneva Retiree Cohort. Serum GSLQPIIK levels did not correlate with total periostin, hip BMD, and the bone markers PINP and CTX. However, GSLQPIIK was negatively correlated (p values ranging from 0.007 to 0.03) with Hr-pQCT measures of tibia and radius cortical bone, but not with trabecular parameters. We have developed the first assay for the detection of periostin fragments generated by cathepsin K. Because serum levels of this new marker significantly correlated with cortical bone measurements in postmenopausal women, it may prove to be useful for the clinical investigation of patients with osteoporosis.

Serum Levels of a Cathepsin-K Generated Periostin Fragment Predict Incident Low-Trauma Fractures in Postmenopausal Women Independently of BMD and FRAX

Periostin is a matricellular protein involved in bone formation and bone matrix organization, but it is also produced by other tissues. Its circulating levels have been weakly associated with bone microstructure and prevalent fractures, possibly because periostin measured by the current commercial assays does not specifically reflect bone metabolism. In this context, we developed a new ELISA for a periostin fragment resulting from cathepsin K digestion (K-Postn). We hypothesized that circulating K-Postn levels could be associated with bone fragility. A total of 695 women (age 65.0 ± 1.5 years), enrolled in the Geneva Retirees Cohort (GERICO), were prospectively evaluated over 4.7 ± 1.9 years for the occurrence of low-trauma fractures. At baseline, we measured serum periostin, K-Postn, and bone turnover markers (BTMs), distal radius and tibia microstructure by HR-pQCT, hip and lumbar spine aBMD by DXA, and estimated fracture probability using the Fracture Risk Assessment Tool (FRAX). Sixty-six women sustained a low-trauma clinical fracture during the follow-up. Total periostin was not associated with fractures (HR [95% CI] per SD: 1.19 [0.89 to 1.59], p = 0.24). In contrast, K-Postn was significantly higher in the fracture versus nonfracture group (57.5 ± 36.6 ng/mL versus 42.5 ± 23.4 ng/mL, p < 0.001) and associated with fracture risk (HR [95%CI] per SD: 2.14 [1.54 to 2.97], p < 0.001). After adjustment for aBMD, FRAX, bone microstructure, or BTMs, K-Postn remained significantly associated with fracture risk. The performance of the fracture prediction models was improved by adding K-Postn to aBMD or FRAX (Harrell C index for fracture: 0.70 for aBMD + K-Post versus 0.58 for aBMD alone, p = 0.001; 0.73 for FRAX + K-Postn versus 0.65 for FRAX alone, p = 0.005). Circulating K-Postn predicts incident fractures independently of BMD, BTMs, and FRAX in postmenopausal women. Hence measurement of a periostin fragment resulting from in vivo cathepsin K digestion may help to identify subjects at high risk of fracture. © 2017 American Society for Bone and Mineral Research.

Retrospective evaluation of serum CTX levels after denosumab discontinuation in patients with or without prior exposure to bisphosphonates

Discontinuation of denosumab (Dmab) therapy is associated with lower serum CTX levels in osteoporotic patients previously exposed to bisphosphonates compared to those who were not.

INTRODUCTION

Discontinuation of Dmab therapy is followed by a transient increase of bone turnover markers (BTMs) above pretreatment values, together with accelerated bone loss, and potentially an increased risk of multiple vertebral fractures. Since a substantial proportion of patients discontinuing Dmab have previously been exposed to bisphosphonates (BPs), we hypothesized that previous BP therapy could attenuate this increase in bone turnover because of the prolonged biological effects of BPs on bone.

METHODS

In a retrospective observation, we assessed serum CTX levels between 7 and 24 months after the last Dmab injection in 37 patients (33 women and 4 men, aged 50 to 84 years). CTX levels were analyzed according to the number of Dmab injections (1 or multiple) and previous exposure to BPs.

RESULTS

In 8 patients who had received only 1 Dmab injection, 7 out of 8 were previously on BPs and none of them showed CTX values above the premenopausal range after Dmab discontinuation. CTX also remained in the premenopausal range in 14 out of 17 patients who discontinued Dmab after multiple (4.1 ± 1.4, range 2-7) injections but were previously exposed to BPs (mean exposure 6.9 ± 5.8 years, range 11 months-15 years; mean time interval between BP exposure and Dmab initiation 25 ± 10 months, range 0-48). In contrast, in 12 patients who discontinued Dmab after multiple (5, range 3-9) injections without prior exposure to BPs, mean CTX levels as measured on average 11.3 months (range 6-23) after the last Dmab injection were above the upper limit of premenopausal range (mean +114%, range 28-320%, p = 0.003-0.005 vs previous BPs).

CONCLUSION

The higher CTX levels occurring after Dmab discontinuation in patients who have received multiple injections may be prevented by prior exposure to BPs. This observation may be related to the persistent effects of BPs on bone that prevent the resorbing activity of newly formed osteoclasts when RANK Ligand is no more antagonized.

Cathepsin K Controls Cortical Bone Formation by Degrading Periostin

Although inhibitors of bone resorption concomitantly reduce bone formation because of the coupling between osteoclasts and osteoblasts, inhibition or deletion of cathepsin k (CatK) stimulates bone formation despite decreasing resorption. The molecular mechanisms responsible for this increase in bone formation, particularly at periosteal surfaces where osteoclasts are relatively poor, remain unclear. Here we show that CatK pharmacological inhibition or deletion (Ctsk^-/- mice) potentiates mechanotransduction signals mediating cortical bone formation. We identify periostin (Postn) as a direct molecular target for degradation by CatK and show that CatK deletion increases Postn and β-catenin expression in vivo, particularly at the periosteum. In turn, Postn deletion selectively abolishes cortical, but not trabecular, bone formation in CatK-deficient mice. Taken together, these data indicate that CatK not only plays a major role in bone remodeling but also modulates modeling-based cortical bone formation by degrading periostin and thereby moderating Wnt-β-catenin signaling. These findings provide novel insights into the role of CatK on bone homeostasis and the mechanisms of increased cortical bone volume with CatK mutations and pharmacological inhibitors. © 2017 American Society for Bone and Mineral Research.

Mechanisms of diabetes mellitus-induced bone fragility

The risk of fragility fractures is increased in patients with either type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM). Although BMD is decreased in T1DM, BMD in T2DM is often normal or even slightly elevated compared with an age-matched control population. However, in both T1DM and T2DM, bone turnover is decreased and the bone material properties and microstructure of bone are altered; the latter particularly so when microvascular complications are present. The pathophysiological mechanisms underlying bone fragility in diabetes mellitus are complex, and include hyperglycaemia, oxidative stress and the accumulation of advanced glycation endproducts that compromise collagen properties, increase marrow adiposity, release inflammatory factors and adipokines from visceral fat, and potentially alter the function of osteocytes. Additional factors including treatment-induced hypoglycaemia, certain antidiabetic medications with a direct effect on bone and mineral metabolism (such as thiazolidinediones), as well as an increased propensity for falls, all contribute to the increased fracture risk in patients with diabetes mellitus.

Peripheral skeleton bone strength is positively correlated with total and dairy protein intakes in healthy postmenopausal women

BACKGROUND

Bone mineral content (BMC) and bone mineral density (BMD) are positively correlated with dietary protein intakes, which account for 1-8% of BMC and BMD variances. However, the relation between bone strength and microstructure, which are variables that are not captured by areal bone mineral density (aBMD), and dietary protein intakes, particularly from specific dietary sources, has not been clearly established.

OBJECTIVE

We investigated the association between the peripheral skeleton-predicted failure load and stiffness, bone microstructure, and dietary protein intakes from various origins (animal, divided into dairy and nondairy, and vegetable origins) in healthy postmenopausal women.

DESIGN

In a cross-sectional study in 746 Caucasian women aged 65.0 ± 1.4 y, we measured the aBMD with the use of dual-energy X-ray absorptiometry, the distal radius and tibia bone microstructures with the use of high-resolution peripheral quantitative computerized tomography, and bone strength with the use of a finite element analysis, and we evaluated dietary protein and calcium with the use of a validated food-frequency questionnaire.

RESULTS

Mean dietary calcium and protein intakes were greater than recommended amounts for this class of age. The predicted failure load and stiffness at the distal radius and tibia were positively associated with total, animal, and dairy protein intakes but not with vegetable protein intake. Failure load differences were accompanied by modifications of the aBMD and of cortical and trabecular bone microstructures. The associations remained statistically significant after adjustment for weight, height, physical activity, menopause duration, calcium intake, and the interaction between calcium and protein intake. A principal component analysis of the volumetric BMD and bone microstructure indicated that trabecular bone mainly contributed to the positive association between protein intakes and bone strength.

CONCLUSIONS

These results, which were recorded in a very homogeneous population of healthy postmenopausal women, indicate that there is a beneficial effect of animal and dairy protein intakes on bone strength and microstructure. Specifically, there is a positive association between the bone failure load and stiffness of the peripheral skeleton and dietary protein intake, which is mainly related to changes in the trabecular microstructure. This trial was registered at www.controlled-trials.com as ISRCTN11865958.

Influence of Fatigue Loading and Bone Turnover on Bone Strength and Pattern of Experimental Fractures of the Tibia in Mice

Bone fragility depends on bone mass, structure, and material properties, including damage. The relationship between bone turnover, fatigue damage, and the pattern and location of fractures, however, remains poorly understood. We examined these factors and their integrated effects on fracture strength and patterns in tibia. Adult male mice received RANKL (2 mg/kg/day), OPG-Fc (5 mg/kg 2×/week), or vehicle (Veh) 2 days prior to fatigue loading of one tibia by in vivo axial compression, with treatments continuing up to 28 more days. One day post fatigue, crack density was similarly increased in fatigued tibiae from all treatment groups. After 28 days, the RANKL group exhibited reduced bone mass and increased crack density, resulting in reduced bone strength, while the OPG-Fc group had greater bone mass and bone strength. Injury repair altered the pattern and location of fractures created by ex vivo destructive testing, with fractures occurring more proximally and obliquely relative to non-fatigued tibia. A similar pattern was observed in both non-fatigued and fatigued tibia of RANKL. In contrast, OPG-Fc prevented this fatigue-related shift in fracture pattern by maintaining fractures more distal and transverse. Correlation analysis showed that bone strength was predominantly determined by aBMD with minor contributions from structure and intrinsic strength as measured by nanoindentation and cracks density. In contrast, fracture location was predicted equally by aBMD, crack density and intrinsic modulus. The data suggest that not only bone strength but also the fracture pattern depends on previous damage and the effects of bone turnover on bone mass and structure. These observations may be relevant to further understand the mechanisms contributing to fracture pattern in long bone with different levels of bone remodeling, including atypical femur fracture.

The role of biochemical of bone turnover markers in osteoporosis and metabolic bone disease: a consensus paper of the Belgian Bone Club

The exact role of biochemical markers of bone turnover in the management of metabolic bone diseases remains a topic of controversy. In this consensus paper, the Belgian Bone Club aimed to provide a state of the art on the use of these biomarkers in different clinical or physiological situations like in postmenopausal women, osteoporosis in men, in elderly patients, in patients suffering from bone metastasis, in patients with chronic renal failure, in pregnant or lactating women, in intensive care patients, and in diabetics. We also gave our considerations on the analytical issues linked to the use of these biomarkers, on potential new emerging biomarkers, and on the use of bone turnover biomarkers in the follow-up of patients treated with new drugs for osteoporosis.

MECHANISMS IN ENDOCRINOLOGY: Mechanisms and evaluation of bone fragility in type 1 diabetes mellitus

Subjects with type 1 diabetes mellitus (T1DM) have decreased bone mineral density and an up to sixfold increase in fracture risk. Yet bone fragility is not commonly regarded as another unique complication of diabetes. Both animals with experimentally induced insulin deficiency syndromes and patients with T1DM have impaired osteoblastic bone formation, with or without increased bone resorption. Insulin/IGF1 deficiency appears to be a major pathogenetic mechanism involved, along with glucose toxicity, marrow adiposity, inflammation, adipokine and other metabolic alterations that may all play a role on altering bone turnover. In turn, increasing physical activity in children with diabetes as well as good glycaemic control appears to provide some improvement of bone parameters, although robust clinical studies are still lacking. In this context, the role of osteoporosis drugs remains unknown.

Myostatin antibody (LY2495655) in older weak fallers: a proof-of-concept, randomised, phase 2 trial

BACKGROUND

Myostatin inhibits skeletal muscle growth. The humanised monoclonal antibody LY2495655 (LY) binds and neutralises myostatin. We aimed to test whether LY increases appendicular lean body mass (aLBM) and improves physical performance in older individuals who have had recent falls and low muscle strength and power.

METHODS

In this proof-of-concept, randomised, placebo-controlled, double-blind, parallel, multicentre, phase 2 study, we recruited patients aged 75 years or older who had fallen in the past year from 21 investigator sites across Argentina, Australia, France, Germany, Sweden, and the USA. Eligible patients had low performance on hand grip strength and chair rise tests, tested with the procedure described by Guralnik and colleagues. Participants were stratified by country, age, hand grip strength, and performance on the chair rise test, and were randomly assigned (1:1) by a computer-generated random sequence to receive subcutaneous injections of placebo or 315 mg LY at weeks 0 (randomisation visit), 4, 8, 12, 16, and 20, followed by 16 weeks observation. The primary outcome was change in aLBM from baseline to 24 weeks. We measured physical performance as secondary outcomes (four-step stair climbing time, usual gait speed, and time to rise five times from a chair without arms, or with arms for participants unable to do it without arms) and exploratory outcomes (12-step stair climbing test, 6-min walking distance, fast gait speed, hand grip strength, and isometric leg extension strength). Efficacy analyses included all randomly assigned patients who received at least one dose and had a baseline and at least one subsequent measure. The primary analysis and all other tests of treatment effect (except physical performance tests) were done at a two-sided alpha level of 0·05. Tests of treatment effect on physical performance tests were done at a pre-specified two-sided alpha level of 0·1. This trial is registered with ClinicalTrials.gov, number NCT01604408.

FINDINGS

Between June 19, 2012, and Dec 12, 2013, we screened 365 patients. 99 were randomly assigned to receive placebo and 102 to receive LY. Treatment was completed in 85 (86%) of patients given placebo and in 82 (80%) given LY. At 24 weeks, the least-squares mean change in aLBM was -0·123 kg (95% CI -0·287 to 0·040) in the placebo group and 0·303 kg (0·135 to 0·470) in the LY group, a difference of 0·43 kg (95% CI 0·192 to 0·660; p<0·0001). Stair climbing time (four-step and 12-step tests), chair rise with arms, and fast gait speed improved significantly from baseline to week 24 with differences between LY and placebo of respectively -0·46 s (p=0·093), -1·28 s (p=0·011), -4·15 s (p=0·054), and 0·05 m/s (p=0·088). No effect was detected for other performance-based measures. Injection site reactions were recorded in nine (9%) patients given placebo and in 31 (30%) patients given LY (p<0·0001), and were generally mild, and led to treatment discontinuation in two patients given LY.

INTERPRETATION

Our findings show LY treatment increases lean mass and might improve functional measures of muscle power. Although additional studies are needed to confirm these results, our data suggest LY should be tested for its potential ability to reduce the risk of falls or physical dependency in older weak fallers.

FUNDING

Eli Lilly and Company.

Periostin expression contributes to cortical bone loss during unloading

Periostin (a product of Postn gene) is a matricellular protein which is increased in periosteal osteoblasts and osteocytes upon mechanical stimulation. We previously reported that periostin-deficient mice (Postn(-/-)) have low bone mass and a diminished response to physical activity due to a lack of sclerostin (a product of Sost gene) inhibition by mechanical loading. Here we hypothesized that periostin could play a central role in the control of bone loss during unloading induced by hindlimb suspension (HU). In Postn(+/+) mice (wildtype littermate), HU significantly decreased femur BMD, as well as trabecular BV/TV and thickness (Tb.Th). Cortical bone volume and thickness at the femoral midshaft, also significantly decreased. These changes were explained by an inhibition of endocortical and periosteal bone formation activity and correlated with a decrease of Postn expression and a consecutive increase in Sost early after HU. Whereas trabecular bone loss in Postn(-/-) mice was comparable to Postn(+/+) mice, HU did not significantly alter cortical bone microstructure and strength in Postn(-/-) mice. Bone formation remained unchanged in these mice, as Sost did not increase in the absence of periostin. In contrast, changes in Dkk1, Rankl and Opg expression in response to HU were similar to Postn(+/+) mice, indicating that changes in periostin expression were quite specifically related to changes in Sost. In conclusion, HU inhibits periostin expression, which in turn plays an important role in cortical bone loss through an increase in Sost. These results further indicate that periostin is an essential mediator of cortical bone response to mechanical forces (loading and unloading).

Regulation of beta catenin signaling and parathyroid hormone anabolic effects in bone by the matricellular protein periostin

Periostin (Postn) is a matricellular protein preferentially expressed by osteocytes and periosteal osteoblasts in response to mechanical stimulation and parathyroid hormone (PTH). Whether and how periostin expression influences bone anabolism, however, remains unknown. We investigated the skeletal response of adult Postn −/− and Postn +/+ mice to intermittent PTH. Compared with Postn +/+ , Postn −/− mice had a lower bone mass, cortical bone volume, and strength response to PTH. PTH-stimulated bone-forming indices were all significantly lower in Postn −/− mice, particularly at the periosteum. Furthermore, in vivo stimulation of Wnt-β-catenin signaling by PTH, as evaluated in TOPGAL reporter mice, was inhibited in the absence of periostin ( TOPGAL;Postn −/− mice). PTH stimulated periostin and inhibited MEF2C and sclerostin (Sost) expression in bone and osteoblasts in vitro. Recombinant periostin also suppressed Sost expression, which was mediated through the integrin αVβ3 receptor, whereas periostin-blocking antibody prevented inhibition of MEF2C and Sost by PTH. In turn, administration of a Sost-blocking antiboby partially restored the PTH-mediated increase in bone mass in Postn −/− mice. In addition, primary osteoblasts from Postn −/− mice showed a lower proliferation, mineralization, and migration, both spontaneously and in response to PTH. Osteoblastic gene expression levels confirmed a defect of Postn −/− osteoblast differentiation with and without PTH, as well as an increased osteoblast apoptosis in the absence of periostin. These data elucidate the complex role of periostin on bone anabolism, through the regulation of Sost, Wnt-β-catenin signaling, and osteoblast differentiation.

A botulinum toxin-derived targeted secretion inhibitor downregulates the GH/IGF1 axis

Botulinum neurotoxins (BoNTs) are zinc endopeptidases that block release of the neurotransmitter acetylcholine in neuromuscular synapses through cleavage of soluble N-ethylmaleimide-sensitive fusion (NSF) attachment protein receptor (SNARE) proteins, which promote fusion of synaptic vesicles to the plasma membrane. We designed and tested a BoNT-derived targeted secretion inhibitor (TSI) targeting pituitary somatotroph cells to suppress growth hormone (GH) secretion and treat acromegaly. This recombinant protein, called SXN101742, contains a modified GH-releasing hormone (GHRH) domain and the endopeptidase domain of botulinum toxin serotype D (GHRH-LHN/D, where HN/D indicates endopeptidase and translocation domain type D). In vitro, SXN101742 targeted the GHRH receptor and depleted a SNARE protein involved in GH exocytosis, vesicle-associated membrane protein 2 (VAMP2). In vivo, administering SXN101742 to growing rats produced a dose-dependent inhibition of GH synthesis, storage, and secretion. Consequently, hepatic IGF1 production and resultant circulating IGF1 levels were reduced. Accordingly, body weight, body length, organ weight, and bone mass acquisition were all decreased, reflecting the biological impact of SXN101742 on the GH/IGF1 axis. An inactivating 2-amino acid substitution within the zinc coordination site of the endopeptidase domain completely abolished SXN101742 inhibitory actions on GH and IGF1. Thus, genetically reengineered BoNTs can be targeted to nonneural cells to selectively inhibit hormone secretion, representing a new approach to treating hormonal excess.

Deletion of β-adrenergic receptor 1, 2, or both leads to different bone phenotypes and response to mechanical stimulation

As they age, mice deficient for the β2-adrenergic receptor (Adrb2(-/-) ) maintain greater trabecular bone microarchitecture, as a result of lower bone resorption and increased bone formation. The role of β1-adrenergic receptor signaling and its interaction with β2-adrenergic receptor on bone mass regulation, however, remains poorly understood. We first investigated the skeletal response to mechanical stimulation in mice deficient for β1-adrenergic receptors and/or β2-adrenergic receptors. Upon axial compression loading of the tibia, bone density, cancellous and cortical microarchitecture, as well as histomorphometric bone forming indices, were increased in both Adrb2(-/-) and wild-type (WT) mice, but not in Adrb1(-/-) nor in Adrb1b2(-/-) mice. Moreover, in the unstimulated femur and vertebra, bone mass and microarchitecture were increased in Adrb2(-/-) mice, whereas in Adrb1(-/-) and Adrb1b2(-/-) double knockout mice, femur bone mineral density (BMD), cancellous bone volume/total volume (BV/TV), cortical size, and cortical thickness were lower compared to WT. Bone histomorphometry and biochemical markers showed markedly decreased bone formation in Adrb1b2(-/-) mice during growth, which paralleled a significant decline in circulating insulin-like growth factor 1 (IGF-1) and IGF-binding protein 3 (IGF-BP3). Finally, administration of the β-adrenergic agonist isoproterenol increased bone resorption and receptor activator of NF-κB ligand (RANKL) and decreased bone mass and microarchitecture in WT but not in Adrb1b2(-/-) mice. Altogether, these results demonstrate that β1- and β2-adrenergic signaling exert opposite effects on bone, with β1 exerting a predominant anabolic stimulus in response to mechanical stimulation and during growth, whereas β2-adrenergic receptor signaling mainly regulates bone resorption during aging.

Early post-transplantation hypophosphatemia is associated with elevated FGF-23 levels

BACKGROUND

We examined the hypothesis that high FGF-23 levels early after transplantation contribute to the onset of hypophosphatemia, independently of parathyroid hormone (PTH) and other factors regulating phosphate metabolism.

METHODS

We measured serum phosphate levels (sPi), renal tubular reabsorption of Pi (TmPi/GFR), estimated GFR (eGFR), intact PTH (iPTH), calcitriol, intact (int) and C-terminal (Cter) FGF-23, dietary Pi intake and cumulative doses of glucocorticoids in 69 patients 12 days (95% confidence interval, 10-13) after renal transplantation.

RESULTS

Hypophosphatemia was observed in 43 (62%) of the patients 12 days after transplantation. Compared with non-hypophosphatemic subjects, their post-transplantation levels of intact and CterFGF-23 were higher (195 (108-288) vs 48 (40-64) ng/l, P<0.002 for intFGF-23; 205 (116-384) vs 81 (55-124) U/ml, P<0.002, for CterFGF-23). In all subjects, Cter and intFGF-23 correlated inversely with sPi (r=-0.35, P<0.003; -0.35, P<0.003, respectively), and TmPi/GFR (r=-0.50, P<0.001; -0.54, P<0.001, respectively). In multivariate models, sPi and TmPi/GFR were independently associated with FGF-23, iPTH and eGFR. Pre-transplant iPTH levels were significantly higher in patients developing hypophosphatemia after renal transplantation. Pre-transplant levels of FGF-23 were not associated with sPi at the time of transplantation.

CONCLUSION

In addition to PTH, elevated FGF-23 may contribute to hypophosphatemia during the early post-renal transplant period.

Effects of long-term supplementation with omega-3 fatty acids on longitudinal changes in bone mass and microstructure in mice

A diet rich in omega-3s has previously been suggested to prevent bone loss. However, evidence for this has been limited by short exposure to omega-3 fatty acids (FAs). We investigated whether a diet enriched in eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) for the entire adult life of mice could improve bone microstructure and strength. Thirty female mice received a diet enriched in DHA or EPA or an isocaloric control diet from 3 to 17 months of age. Changes in bone microstructure were analyzed longitudinally and biomechanical properties were analysed by a three-point bending test. Bone remodelling was evaluated by markers of bone turnover and histomorphometry. Trabecular bone volume in caudal vertebrae was improved by EPA or DHA at 8 months (+26.6% and +17.2%, respectively, compared to +3.8% in controls, P=.01), but not thereafter. Trabecular bone loss in the tibia was not prevented by omega-3 FAs (BV/TV -94%, -93% and -97% in EPA, DHA and controls, respectively). EPA improved femur cortical bone volume (+8.1%, P<.05) and thickness (+4.4%, P<.05) compared to controls. EPA, but not DHA, reduced age-related decline of osteocalcin (-70% vs. -83% in controls, P<.05). EPA and DHA increased leptin levels (7.3±0.7 and 8.5±0.5 ng ml⁻¹, respectively, compared to 4.5±0.9 ng ml⁻¹ in controls, P=.001); however, only EPA further increased IGF-1 levels (739±108 ng ml⁻¹, compared to 417±58 ng ml⁻¹ in controls, P=.04). These data suggest that long-term intake of omega-3 FA, particularly EPA, may modestly improve the structural and mechanical properties of cortical bone by an increase in leptin and IGF-1 levels, without affecting trabecular bone loss.

Are osteoclasts needed for the bone anabolic response to parathyroid hormone? A study of intermittent parathyroid hormone with denosumab or alendronate in knock-in mice expressing humanized RANKL

PTH stimulates osteoblastic cells to form new bone and to produce osteoblast-osteoclast coupling factors such as RANKL. Whether osteoclasts or their activity are needed for PTH anabolism remains uncertain. We treated ovariectomized huRANKL knock-in mice with a human RANKL inhibitor denosumab (DMAb), alendronate (Aln), or vehicle for 4 weeks, followed by co-treatment with intermittent PTH for 4 weeks. Loss of bone mass and microarchitecture was prevented by Aln and further significantly improved by DMAb. PTH improved bone mass, microstructure, and strength, and was additive to Aln but not to DMAb. Aln inhibited biochemical and histomorphometrical indices of bone turnover,--i.e. osteocalcin and bone formation rate (BFR) on cancellous bone surfaces-, and Dmab inhibited them further. However Aln increased whereas Dmab suppressed osteoclast number and surfaces. PTH significantly increased osteocalcin and bone formation indices, in the absence or presence of either antiresorptive, although BFR remained lower in presence of Dmab. To further evaluate PTH effects in the complete absence of osteoclasts, high dose PTH was administered to RANK(-/-) mice. PTH increased osteocalcin similarly in RANK(-/-) and WT mice. It also increased BMD in RANK(-/-) mice, although less than in WT. These results further indicate that osteoclasts are not strictly required for PTH anabolism, which presumably still occurs via stimulation of modeling-based bone formation. However the magnitude of PTH anabolic effects on the skeleton, in particular its additive effects with antiresorptives, depends on the extent of the remodeling space, as determined by the number and activity of osteoclasts on bone surfaces.

Beta-arrestin-biased parathyroid hormone ligands: a new approach to the development of agents that stimulate bone formation

Because daily treatment with parathyroid hormone (PTH) increases bone mass and decreases fracture risk, physicians use this agent to treat osteoporosis. However, PTH stimulates both bone-forming and bone-resorbing cells, complicating its clinical use. New results show that, in mice, a so-called biased agonist (PTH-betaarr) that selectively activates beta-arrestin -dependent signaling leads to PTH-induced trabecular bone formation without a simultaneous increase in bone resorption. This targeted approach may pave the way for future pharmacological developments in the treatment of osteoporosis.

The matricellular protein periostin is required for sost inhibition and the anabolic response to mechanical loading and physical activity

Periostin (gene Postn) is a secreted extracellular matrix protein involved in cell recruitment and adhesion and plays an important role in odontogenesis. In bone, periostin is preferentially expressed in the periosteum, but its functional significance remains unclear. We investigated Postn(-/-) mice and their wild type littermates to elucidate the role of periostin in the skeletal response to moderate physical activity and direct axial compression of the tibia. Furthermore, we administered a sclerostin-blocking antibody to these mice in order to demonstrate the influence of sustained Sost expression in their altered bone phenotypes. Cancellous and cortical bone microarchitecture as well as bending strength were altered in Postn(-/-) compared with Postn(+/+) mice. Exercise and axial compression both significantly increased bone mineral density and trabecular and cortical microarchitecture as well as biomechanical properties of the long bones in Postn(+/+) mice by increasing the bone formation activity, particularly at the periosteum. These changes correlated with an increase of periostin expression and a consecutive decrease of Sost in the stimulated bones. In contrast, mechanical stimuli had no effect on the skeletal properties of Postn(-/-) mice, where base-line expression of Sost levels were higher than Postn(+/+) and remained unchanged following axial compression. In turn, the concomitant injection of sclerostin-blocking antibody rescued the bone biomechanical response in Postn(-/-) mice. Taken together, these results indicate that the matricellular periostin protein is required for Sost inhibition and thereby plays an important role in the determination of bone mass and microstructural in response to loading.

Neuropeptide Y knockout mice reveal a central role of NPY in the coordination of bone mass to body weight

Changes in whole body energy levels are closely linked to alterations in body weight and bone mass. Here, we show that hypothalamic signals contribute to the regulation of bone mass in a manner consistent with the central perception of energy status. Mice lacking neuropeptide Y (NPY), a well-known orexigenic factor whose hypothalamic expression is increased in fasting, have significantly increased bone mass in association with enhanced osteoblast activity and elevated expression of bone osteogenic transcription factors, Runx2 and Osterix. In contrast, wild type and NPY knockout (NPY (-/-)) mice in which NPY is specifically over expressed in the hypothalamus (AAV-NPY+) show a significant reduction in bone mass despite developing an obese phenotype. The AAV-NPY+ induced loss of bone mass is consistent with models known to mimic the central effects of fasting, which also show increased hypothalamic NPY levels. Thus these data indicate that, in addition to well characterized responses to body mass, skeletal tissue also responds to the perception of nutritional status by the hypothalamus independently of body weight. In addition, the reduction in bone mass by AAV NPY+ administration does not completely correct the high bone mass phenotype of NPY (-/-) mice, indicating the possibility that peripheral NPY may also be an important regulator of bone mass. Indeed, we demonstrate the expression of NPY specifically in osteoblasts. In conclusion, these data identifies NPY as a critical integrator of bone homeostatic signals; increasing bone mass during times of obesity when hypothalamic NPY expression levels are low and reducing bone formation to conserve energy under 'starving' conditions, when hypothalamic NPY expression levels are high.

Beta-arrestin2 regulates parathyroid hormone effects on a p38 MAPK and NFkappaB gene expression network in osteoblasts

Interaction of the cytoplasmic adaptor molecule beta-arrestin2 with the activated parathyroid hormone (PTH)/PTHrP receptor inhibits G protein mediated signaling and triggers MAPKs signaling. In turn, the effects of both intermittent (i.) and continuous (c.) PTH on bone are altered in beta-arrestin2-deficient (Arrb2(-/-)) mice. To elucidate the expression profile of bone genes responsive to PTH and targeted for regulation by beta-arrestin2, we performed microarray analysis using total RNA from primary osteoblastic cells isolated from wild-type (WT) and Arrb2(-/-) mice. By comparing gene expression profiles in cells exposed to i.PTH, c.PTH or vehicle (Veh) for 2 weeks, we found that i.PTH specifically up-regulated 215 sequences (including beta-arrestin2) and down-regulated 200 sequences in WT cells, about two-thirds of them being under the control of beta-arrestin2. In addition, beta-arrestin2 appeared necessary to the down-regulation of a genomic cluster coding for small leucin-rich proteins (SLRPs) including osteoglycin, osteomodulin and asporin. Pathway analyses identified a main gene network centered on p38 MAPK and NFkappaB that requires beta-arrestin2 for up- or down-regulation by i.PTH, and a smaller network of PTH-regulated genes centered on TGFB1, that is normally repressed by beta-arrestin2. In contrast the expression of some known PTH gene targets regulated by the cAMP/PKA pathway was not affected by the presence or absence of beta-arrestin2 in osteoblasts. These results indicate that beta-arrestin2 targets prominently p38 MAPK- and NFkappaB-dependent expression in osteoblasts exposed to i.PTH, and delineates new molecular mechanisms to explain the anabolic and catabolic effects of PTH on bone.

Mice lacking beta-adrenergic receptors have increased bone mass but are not protected from deleterious skeletal effects of ovariectomy

Activation of beta2-adrenergic receptors inhibits osteoblastic bone formation and enhances osteoclastic bone resorption. Whether beta-blockers inhibit ovariectomy-induced bone loss and decrease fracture risk remains controversial. To further explore the role of beta-adrenergic signaling in skeletal acquisition and response to estrogen deficiency, we evaluated mice lacking the three known beta-adrenergic receptors (beta-less). Body weight, percent fat, and bone mineral density were significantly higher in male beta-less than wild-type (WT) mice, more so with increasing age. Consistent with their greater fat mass, serum leptin was significantly higher in beta-less than WT mice. Mid-femoral cross-sectional area and cortical thickness were significantly higher in adult beta-less than WT mice, as were femoral biomechanical properties (+28 to +49%, P < 0.01). Young male beta-less had higher vertebral (1.3-fold) and distal femoral (3.5-fold) trabecular bone volume than WT (P < 0.001 for both) and lower osteoclast surface. With aging, these differences lessened, with histological evidence of increased osteoclast surface and decreased bone formation rate at the distal femur in beta-less vs. WT mice. Serum tartrate-resistance alkaline phosphatase-5B was elevated in beta-less compared with WT mice from 8-16 wk of age (P < 0.01). Ovariectomy inhibited bone mass gain and decreased trabecular bone volume/total volume similarly in beta-less and WT mice. Altogether, these data indicate that absence of beta-adrenergic signaling results in obesity and increased cortical bone mass in males but does not prevent deleterious effects of estrogen deficiency on trabecular bone microarchitecture. Our findings also suggest direct positive effects of weight and/or leptin on bone turnover and cortical bone structure, independent of adrenergic signaling.

Leptin and the sympathetic connection of fat to bone

Loss of body weight is associated with bone loss, and body weight gain is associated with increased bone formation. The molecular mechanisms linking body weight, body composition, and bone density are now better understood. Lean mass is likely to have a significant, local effect on bone modeling and remodeling through mechanotransduction pathways. In contrast to the local regulation of bone formation and resorption by muscle-derived stimuli, peripheral body fat appears to influence bone mass via secretion of systemic, endocrine factors that link body weight to bone density even in non-weight bearing regions (e.g., the forearm). The cytokine-like hormone leptin, which is secreted by fat cells, is an important candidate molecule linking changes in body composition with bone formation and bone resorption. Increases in body fat increase leptin levels and stimulate periosteal bone formation through its direct anabolic effects on osteoblasts, and through central (CNS) effects including the stimulation of the GH-IGF-1 axis and suppression of neuropeptide Y, a powerful inhibitor of bone formation. Stimulation of beta2-adrenergic receptors through central (hypothalamic) leptin receptors does, however, increase remodeling of trabecular bone, resulting in a lower cancellous bone volume that may be better adapted to a concomitantly larger cortical bone compartment. These findings suggest that body weight and body fat can regulate bone mass and structure through molecular pathways that are independent of load-bearing. Furthermore, pharmacological manipulation of the signaling pathways activated by leptin may have significant potential for the treatment and prevention of bone loss.

Contribution of gender-specific genetic factors to osteoporosis risk

Common diseases result from the complex relationship between genetic and environmental factors. The aim of this review is to provide perspective for a conceptual framework aimed at studying the interplay of gender-specific genetic and environmental factors in the etiology of complex disease, using osteoporosis as an example. In recent years, gender differences in the heritability of the osteoporosis-related phenotypes have been reported and sex-specific quantitative-trait loci were discovered by linkage studies in humans and mice. Results of numerous allelic association studies also differed by gender. In most cases, it was not clear whether or not this phenomenon should be attributed to the effect of sex-chromosomes, sex hormones, or other intrinsic or extrinsic differences between the genders, such as the level of bioavailable estrogen and of physical activity. We conclude that there is need to consider gender-specific genetic and environmental factors in the planning of future association studies on the etiology of osteoporosis and other complex diseases prevalent in the general population.

Adrenergic control of bone remodeling and its implications for the treatment of osteoporosis

Evidence that leptin regulates bone turnover in part through a central nervous system (CNS)/beta-adrenergic system relay has driven attention towards the potential therapeutic benefits of beta-adrenergic blockade to improve bone mass and strength. beta2- adrenergic receptor-mediated signaling in osteoblasts inhibits bone formation and triggers RANKL-mediated osteoclastogenesis and bone resorption. Mouse models of adrenergic-deficiency, particularly the mouse lacking the beta2-adrenergic receptor, have increased bone mass, more specifically increased trabecular bone volume. In turn, beta-blockers, such as propranolol, were reported to inhibit ovariectomy-induced bone loss. In contrast, a number of experiments in mice and rats suggest that inhibition of beta-adrenergic receptor-mediated signaling does not improve, and could actually be detrimental, for bone mass and microstructure. In humans, epidemiological observations suggested that users of beta-blockers have higher bone mineral density (BMD) and/or a reduced risk of fractures, yet not all studies were concordant. Here we review the evidence for a role of the adrenergic system in the regulation of bone metabolism in vitro and in vivo and provide some new evidence for a dual role of beta-adrenergic receptors 1 and 2 on bone turnover. Furthermore, we will examine the similarities and disparities that may exist in the effects of beta-adrenergic and PTH stimulation on bone metabolism.

Large-scale analysis of association between LRP5 and LRP6 variants and osteoporosis

CONTEXT

Mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) gene cause rare syndromes characterized by altered bone mineral density (BMD). More common LRP5 variants may affect osteoporosis risk in the general population.

OBJECTIVE

To generate large-scale evidence on whether 2 common variants of LRP5 (Val667Met, Ala1330Val) and 1 variant of LRP6 (Ile1062Val) are associated with BMD and fracture risk.

DESIGN AND SETTING

Prospective, multicenter, collaborative study of individual-level data on 37,534 individuals from 18 participating teams in Europe and North America. Data were collected between September 2004 and January 2007; analysis of the collected data was performed between February and May 2007. Bone mineral density was assessed by dual-energy x-ray absorptiometry. Fractures were identified via questionnaire, medical records, or radiographic documentation; incident fracture data were available for some cohorts, ascertained via routine surveillance methods, including radiographic examination for vertebral fractures.

MAIN OUTCOME MEASURES

Bone mineral density of the lumbar spine and femoral neck; prevalence of all fractures and vertebral fractures.

RESULTS

The Met667 allele of LRP5 was associated with reduced lumbar spine BMD (n = 25,052 [number of participants with available data]; 20-mg/cm2 lower BMD per Met667 allele copy; P = 3.3 x 10(-8)), as was the Val1330 allele (n = 24,812; 14-mg/cm2 lower BMD per Val1330 copy; P = 2.6 x 10(-9)). Similar effects were observed for femoral neck BMD, with a decrease of 11 mg/cm2 (P = 3.8 x 10(-5)) and 8 mg/cm2 (P = 5.0 x 10(-6)) for the Met667 and Val1330 alleles, respectively (n = 25 193). Findings were consistent across studies for both LRP5 alleles. Both alleles were associated with vertebral fractures (odds ratio [OR], 1.26; 95% confidence interval [CI], 1.08-1.47 for Met667 [2001 fractures among 20 488 individuals] and OR, 1.12; 95% CI, 1.01-1.24 for Val1330 [1988 fractures among 20,096 individuals]). Risk of all fractures was also increased with Met667 (OR, 1.14; 95% CI, 1.05-1.24 per allele [7876 fractures among 31,435 individuals)]) and Val1330 (OR, 1.06; 95% CI, 1.01-1.12 per allele [7802 fractures among 31 199 individuals]). Effects were similar when adjustments were made for age, weight, height, menopausal status, and use of hormone therapy. Fracture risks were partly attenuated by adjustment for BMD. Haplotype analysis indicated that Met667 and Val1330 variants both independently affected BMD. The LRP6 Ile1062Val polymorphism was not associated with any osteoporosis phenotype. All aforementioned associations except that between Val1330 and all fractures and vertebral fractures remained significant after multiple-comparison adjustments.

CONCLUSIONS

Common LRP5 variants are consistently associated with BMD and fracture risk across different white populations. The magnitude of the effect is modest. LRP5 may be the first gene to reach a genome-wide significance level (a conservative level of significance [herein, unadjusted P < 10(-7)] that accounts for the many possible comparisons in the human genome) for a phenotype related to osteoporosis.

Evidences for a role of p38 MAP kinase in the stimulation of alkaline phosphatase and matrix mineralization induced by parathyroid hormone in osteoblastic cells

Increased bone formation by PTH mainly results from activation of osteoblasts, an effect largely mediated by the cAMP-PKA pathway. Other pathways, however, are likely to be involved in this process. In this study we investigated whether PTH can activate p38 MAPK and the role of this kinase in osteoblastic cells. Bovine PTH(1-34) and forskolin markedly increased alkaline phosphatase (ALP) activity and doubled osteocalcin (Oc) expression in early differentiating MC3T3-E1 cells. These effects were associated with increase in cellular cAMP and activation of the MAP kinases ERK and p38. Activation of these MAP kinases was detectable after 1 h incubation with 10(-7) M PTH and lasted 1-2 h. Activation of p38 was mimicked by 10 microM forskolin and prevented by H89 suggesting a cAMP-PKA-dependent mechanism of p38 activation. Interestingly, PTH-induced ALP stimulation was dose-dependently inhibited by a specific p38 inhibitor with no change in the generation of cAMP and the production of osteocalcin. Similar inhibitory effect was obtained in cells stably expressing a dominant-negative p38 molecule. Finally, treatment of MC3T3-E1 cells with PTH for 3 weeks significantly enhanced matrix mineralization and this effect was markedly reduced by a selective p38 but not a specific MEK inhibitor. In conclusion, data presented in this study indicate that PTH can activate p38 in early differentiating osteoblastic cells. Activation of p38 is cAMP-PKA-dependent and mediates PTH-induced stimulation of ALP which plays a critical role for the calcification of the bone matrix.

Genetic variation at the low-density lipoprotein receptor-related protein 5 (LRP5) locus modulates Wnt signaling and the relationship of physical activity with bone mineral density in men

Polymorphisms in the LRP5 gene have been associated with bone mineral density (BMD) in men and/or women. However, the functional basis for this association remains obscure. We hypothesized that LRP5 alleles could modulate Wnt signaling and the relationship between physical activity and BMD. This genetic association study was performed in the population-based Framingham Study Offspring Cohort, and included a subset of 1797 unrelated individuals who provided blood samples for DNA and who had BMD measurements of the hip and spine. Ten single-nucleotide polymorphisms (SNPs) spanning the LRP5 gene were genotyped and used for association and interaction analyses with BMD by regression methods. LRP5 haplotypes were transiently co-expressed with Wnt3a, MesD and Dkk1 in HEK293 cells and their activity evaluated by the TCF-Lef reporter assay. Six out of ten SNPs in LRP5 were associated with one or more of the femur or spine BMDs in men or women after adjustment for covariates, and these associations differed between genders. In men< or =age 60 years, 3 SNPs were significantly associated with BMD: rs2306862 on Exon 10 with femoral neck BMD (p=0.01) and Ward's BMD (p=0.01); rs4988321/p. V667M with Ward's BMD (p=0.02); and intronic rs901825 with trochanter BMD (p=0.03). In women, 3 SNPs in intron 2 were significantly associated with BMD: rs4988330 for trochanter (p=0.01) and spine BMD (p=0.003); rs312778 with femoral neck BMD (p=0.05); and rs4988331 with spine BMD (p=0.04). For each additional rare allele, BMD changed by 3-5% in males and 2-4% in females. Moreover, there was a significant interaction between physical activity and rs2306862 in exon 10 (p for interaction=0.02) and rs3736228/p. A1330V in exon 18 (p for interaction=0.05) on spine BMD in men. In both cases, the TT genotype was associated with lower BMD in men with higher physical activity scores, conversely with higher BMD in men with lower physical activity scores. In vitro, TCF-Lef activity in presence of Wnt3a was significantly reduced in cells expressing LRP5 haplotypes carrying the T allele of exon 10 and 18 compared to the wild-type allele, whereas co-expression of Dkk1 completely inhibited Wnt3a response through all LRP5 haplotypes. In summary, genetic variation in exons 10 and 18 of the LRP5 gene modulates Wnt signaling and the relationship between physical activity and BMD in men. These observations suggest that Wnt-LRP5 may play a role in the adaptation of bone to mechanical load in humans, and may explain some gender-related differences in bone mass.

Proline-rich motifs in the parathyroid hormone (PTH)/PTH-related protein receptor C terminus mediate scaffolding of c-Src with beta-arrestin2 for ERK1/2 activation

Parathyroid hormone (PTH) stimulates ERK1/2 through both G-protein signaling and beta-arrestin2-mediated internalization. Beta-arrestin may serve as a scaffold for c-Src. However, the molecular mechanisms for ERK1/2 activation by PTH remain unclear. By using a targeted mutagenesis approach, we investigated the PTH/PTH-related protein receptor (PTH1R) structural determinants for ERK1/2 activation and transcriptional activity in HEK-293 cells. First, ERK1/2 activation was inhibited by PTH1R mutations that specifically abrogate G(q)-protein kinase C signaling without a decrease in cAMP-protein kinase A. Second, PTH1R C-terminal mutations and/or deletions that prevent interaction with beta-arrestin inhibited ERK1/2 activation. Similar results were obtained in HEK-293 cells co-expressing wild-type PTH1R and a dominant-negative beta-arrestin2. Third, the c-Src inhibitor PP2 and a kinase-dead c-SrcK295M mutant co-expressed with wild-type PTH1R both inhibited ERK1/2 activation. Furthermore, c-Src co-precipitated with both PTH1R and beta-arrestin2 in response to PTH. Deleting the PTH1R-proximal C terminus abolished these interactions. However, the need for receptor interaction with beta-arrestin to co-precipitate Src and activate ERK1/2 was obviated by expressing a constitutively active c-SrcY527A mutant, suggesting direct binding of activated Src to PTH1R. Subsequently, we identified and mutated to alanine four proline-rich motifs in the PTH1R distal C terminus, which resulted in loss of both c-Src and arrestin co-precipitation and significantly decreased ERK1/2 activation. These data delineate the multiple PTH1R structural determinants for ERK1/2 activation and newly identify a unique mechanism involving proline-rich motifs in the receptor C terminus for reciprocal scaffolding of c-Src and beta-arrestin2 with a class II G-protein-coupled receptor.

Combined treatment with a beta-blocker and intermittent PTH improves bone mass and microarchitecture in ovariectomized mice

Intermittent administration of parathyroid hormone (PTH) induces bone remodeling and renewed bone modeling, resulting in net bone gain. beta-blockers improve trabecular bone architecture in young ovariectomized mice by preventing the inhibition of bone formation and stimulation of bone resorption induced by the adrenergic system. To test the hypothesis that PTH and beta-blockers may exert synergistic effects on the skeleton, 15-week-old ovariectomized mice were either given oral propranolol (PRO) or left untreated for 8 weeks, adding daily hPTH(1-34) (80 microg/kg/day) or vehicle (VEH) during the last 4 weeks. The skeletal response was evaluated using pDXA, microCT, histomorphometry and biochemical markers. PRO significantly attenuated loss of bone mineral density (BMD) at whole body (WB) (-0.1% in PRO vs. -2.4% in VEH, P < 0.05), but not at spine or femur 4 weeks after OVX. Thereafter, PTH increased BMD at all sites in both PRO- and VEH-treated mice (+6.7% to +14%, P < 0.05 to P < 0.0001 vs. VEH). Over 8 weeks, sequential-combined treatment of PRO and PTH significantly improved BMD over PTH alone at WB (+9.1% vs. +4.4% over baseline, respectively, P < 0.005) and spine (+9% vs. -1.7%, respectively, P < 0.05). These effects were paralleled by a decrease in TRACP5b with PRO (P < 0.05 vs. VEH) and an increase in osteocalcin with PTH, irrespective of PRO (P < 0.0001 vs. VEH). Trabecular bone microarchitecture, such as BV/TV, trabecular number and ConnD, was significantly improved by sequential-combined treatment of PRO and PTH compared to PTH alone. At midshaft femur, both PRO and PTH significantly increased cross-sectional area (CSA), but the effects of the two drugs on CSA and cortical thickness were not additive. Dynamic histomorphometry indicated that bone formation was increased by PTH at both cortical and trabecular surfaces, whereas PRO increased osteoblast number and surface on trabecular surfaces. The combined treatment further improved the extent of mineralization and BFR over PTH alone (P < 0.05) at endocortical surfaces and recapitulated the effects of PTH and PRO alone on trabecular surfaces. These results indicate that beta-adrenergic blockade may partially improve the bone remodeling balance induced by estrogen deficiency. In turn, PRO exerted synergistic effects with intermittent PTH on bone mass and cancellous bone architecture. As such, combined therapy of beta-blockers and PTH may be of interest in the treatment of postmenopausal osteoporosis.

Childhood fractures are associated with decreased bone mass gain during puberty: an early marker of persistent bone fragility?

Whether peak bone mass is low among children with fractures remains uncertain. In a cohort of 125 girls followed over 8.5 years, 42 subjects reported 58 fractures. Among those, BMC gain at multiple sites and vertebral bone size at pubertal maturity were significantly decreased. Hence, childhood fractures may be markers of low peak bone mass acquisition and persistent skeletal fragility.

INTRODUCTION

Fractures in childhood may result from a deficit in bone mass accrual during rapid longitudinal growth. Whether low bone mass persists beyond this period however remains unknown.

MATERIALS AND METHODS

BMC at the spine, radius, hip, and femur diaphysis was prospectively measured over 8.5 years in 125 girls using DXA. Differences in bone mass and size between girls with and without fractures were analyzed using nonparametric tests. The contribution of genetic factors was evaluated by mother-daughter correlations and that of calcium intake by Cox proportional hazard models.

RESULTS

Fifty-eight fractures occurred in 42 among 125 girls (cumulative incidence, 46.4%), one-half of all fractures affecting the forearm and wrist. Girls with and without fractures had similar age, height, weight. and calcium intake at all time-points. Before and during early puberty, BMC and width of the radius diaphysis was lower in the fracture compared with no-fracture group (p < 0.05), whereas aBMD and BMAD were similar in the two groups. At pubertal maturity (Tanner's stage 5, mean age +/- SD, 16.4 +/- 0.5 years), BMC at the ultradistal radius (UD Rad.), femur trochanter, and lumbar spine (LS), and LS projected bone area were all significantly lower in girls with fractures. Throughout puberty, BMC gain at these sites was also decreased in the fracture group (LS, -8.0%, p = 0.015; UD Rad., -12.0%, p = 0.004; trochanter, -8.4%, p = 0.05 versus no fractures). BMC was highly correlated between prepuberty and pubertal maturity (R = 0.54-0.81) and between mature daughters and their mothers (R = 0.32-0.46). Calcium intake was not related to fracture risk.

CONCLUSIONS

Girls with fractures have decreased bone mass gain in the axial and appendicular skeleton and reduced vertebral bone size when reaching pubertal maturity. Taken together with the evidence of tracking and heritability for BMC, these observations indicate that childhood fractures may be markers for low peak bone mass and persistent bone fragility.

LRP5 gene polymorphisms and idiopathic osteoporosis in men

Mutations in the low-density lipoprotein receptor-related protein 5 gene (LRP5) have demonstrated the role of LRP5 in bone mass acquisition. LRP5 variants were recently reported to contribute to the population-based variance in vertebral bone mass and size in males. To investigate whether LRP5 variants are implicated in idiopathic male osteoporosis, we studied 78 men with low BMD (<2.5 T score or < -2 Z score) aged less than 70 years (mean +/- SD: 50 +/- 16 years) in whom secondary causes of osteoporosis had been excluded and 86 controls (51 +/- 10 years). Genotypes and haplotypes were based on LRP5 missense substitutions in exons 9 (c.2047G > A, p.V667M) and 18 (c.4037C > T, p.A1330V), and their association with osteoporosis evaluated after adjustment for multiple clinical and environmental variables using logistic regression. The presence of osteoporosis was significantly associated with LRP5 haplotypes (P = 0.0036) independent of age (P = 0.006), weight (P = 0.004), calcium intake (P = 0.002), alcohol (P = 0.005) and tobacco (P = 0.004) consumption. Accordingly, the odds ratio for osteoporosis was 3.78 (95% CI 1.27-11.26, P < 0.001) in male carriers of haplotype 3 (c.2047A-4037T, n = 20 cases and 12 controls) versus homozygous carriers of haplotype 1 (c.2047G-4037C, n = 42 cases and 61 controls). In conclusion, these data indicate beyond a significant role for environmental factors, an association between LRP5 variants and idiopathic osteoporosis in males, pointing to a role of LRP5 in this disease.

Gene variants for osteoporosis and their pleiotropic effects in aging

The prevalence of osteoporosis is raising worldwide as improving conditions of living and treatment of other common diseases continuously increases life expectancy. Thus, osteoporosis affects most women above 80 years of age and, at the age of 50, the lifetime risk of suffering an osteoporosis-related fracture approaches 50% in women and 20% in men. Numerous genetic, hormonal, nutritional and life-style factors contribute to the acquisition and maintenance of bone mass. Among them, genetic variations explain as much as 70% of the variance for bone mineral density (BMD) in the population. Dozens of quantitative trait loci (QTLs) for BMD have been identified by genome screening and linkage approaches in humans and mice, and more than 100 candidate gene polymorphisms tested for association with BMD and/or fracture. Sequence variants in the vitamin D receptor (VDR), collagen 1 alpha 1 chain (Col1A1), estrogen receptor alpha (ESR1), interleukin-6 (IL-6) and LDL receptor-related protein 5 (LRP5) genes were all found to be significantly associated with differences in BMD and/or fracture risk in multiple replication studies. Moreover, some genes, such as VDR and IL-6, were shown to interact with non-genetic factors, i.e. calcium intake and estrogens, to modulate BMD. Since these gene variants have also been associated with other complex disorders, including cancer and coronary heart disease, they may represent common genetic susceptibility factors exerting pleiotropic effects during the aging process.

Pathogenic mutations and polymorphisms in the lipoprotein receptor-related protein 5 reveal a new biological pathway for the control of bone mass

PURPOSE OF REVIEW

This review summarizes recent findings concerning the genomic variations of the lipoprotein receptor-related protein 5 (LPR5) in relation to bone biology.

RECENT FINDINGS

Mutations in the LRP5 gene causing high bone mass (HBM) and osteoporosis-pseudoglioma (OPPG) underscored the role of the Wnt-LRP5 canonical signaling on bone formation. Additional LRP5 activating mutations have been identified in a variety of sclerosing bone dysplasias, improving the diagnostic classification of these disorders. Association of polymorphisms in LRP5 with bone mineral density indicate that LRP5 genetic variation contribute to the risk of osteoporosis. Transgenic mice carrying the LRP5 HBM mutation have improved bone biomechanical properties, and the molecular mechanisms by which this mutation exerts its effects have been clarified. A number of KO mice have shown the complex effects of the Wnt-LRP5 pathway on bone mass and skeletal morphology. In vitro studies indicate that osteoblasts produce a variety of Wnts, the LRP5 co-receptor frizzled (Fzd), as well as LRP5 and Wnt inhibitors, i.e. dickkopf (Dkk1) and frizzled-related proteins (Sfrps), respectively, and delineate the role of these molecules in regulating the commitment of mesenchymal stem cells along the osteoblastic lineage.

SUMMARY

Identification of pathogenic mutations and allelic variations in LRP5 has improved our understanding of the physiology of bone mass acquisition and the pathophysiology of several bone diseases, including osteoporosis. Understanding how complex interactions between agonistic and inhibitory factors in the Wnt-LRP5 canonical pathway influence osteoblast functions has the potential of providing new anabolic treatments for osteoporosis.