Callus γδ T cells and microbial-induced intestinal Th17 cells improve fracture healing in mice

IL-17A (IL-17), a driver of the inflammatory phase of fracture repair, is produced locally by several cell lineages including γδ T cells and Th17 cells. However, the origin and relevance for fracture repair of these T cells are unknown. Here we show that fractures rapidly expanded callus γδ T cells, which led to increased gut permeability by promoting systemic inflammation. When the microbiota contained the Th17 cell-inducing taxa segmented filamentous bacteria (SFB), activation of γδ T cells was followed by expansion of intestinal Th17 cells, their migration to the callus, and improvement of fracture repair. Mechanistically, fractures increased the S1P-receptor-1 (S1PR1) mediated egress of Th17 cells from the intestine and enhanced their homing to the callus through a CCL20 mediated mechanism. Fracture repair was impaired by deletion of γδ T cells, depletion of the microbiome by antibiotics, blockade of Th17 cell egress from the gut or antibody neutralization of Th17 cell influx into the callus. These findings demonstrated the relevance of the microbiome and T cell trafficking for fracture repair. Modifications of microbiome composition via Th17 cell-inducing bacteriotherapy and avoidance of broad-spectrum antibiotics may represent novel therapeutic strategies to optimize fracture healing.

Impact of Alcohol on Bone Health in People Living With HIV: Integrating Clinical Data From Serum Bone Markers With Morphometric Analysis in a Non-Human Primate Model

People living with HIV (PLWH) represent a vulnerable population to adverse musculoskeletal outcomes due to HIV infection, antiretroviral therapy (ART), and at-risk alcohol use. Developing measures to prevent skeletal degeneration in this group requires a grasp of the relationship between alcohol use and low bone mass in both the PLWH population and its constituents as defined by sex, age, and race. We examined the association of alcohol use with serum biochemical markers of bone health in a diverse cohort of PLWH enrolled in the New Orleans Alcohol Use in HIV (NOAH) study. To explore the effects of alcohol on bone in the context of HIV and ART and the role of estrogen, we conducted a parallel, translational study using simian immunodeficiency virus (SIV)+/ART+ female rhesus macaques divided into four groups: vehicle (Veh)/Sham; chronic binge alcohol (CBA)/Sham; Veh/ovariectomy (OVX); and CBA/OVX. Clinical data showed that both osteocalcin (Ocn) and procollagen type I N-propeptide (PINP) levels were inversely associated with multiple measures of alcohol consumption. Age (>50 years) significantly increased susceptibility to alcohol-associated suppression of bone formation in both female and male PLWH, with postmenopausal status appearing as an additional risk factor in females. Serum sclerostin (Scl) levels correlated positively with measures of alcohol use and negatively with Ocn. Micro-CT analysis of the macaque tibias revealed that although both CBA and OVX independently decreased trabecular number and bone mineral density, only OVX decreased trabecular bone volume fraction and impacted cortical geometry. The clinical data implicate circulating Scl in the pathogenesis of alcohol-induced osteopenia and suggest that bone morphology can be significantly altered in the absence of net change in osteoblast function as measured by serum markers. Inclusion of sophisticated tools to evaluate skeletal strength in clinical populations will be essential to understand the impact of alcohol-induced changes in bone microarchitecture. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

The microbiome restrains melanoma bone growth by promoting intestinal NK and Th1 cell homing to bone

Bone metastases are frequent complications of malignant melanoma leading to reduced quality of life and significant morbidity. Regulation of immune cells by the gut microbiome influences cancer progression, but the role of the microbiome in tumor growth in bone is unknown. Using intracardiac or intratibial injections of B16-F10 melanoma cells into mice, we showed that gut microbiome depletion by broad-spectrum antibiotics accelerated intraosseous tumor growth and osteolysis. Microbiome depletion blunted melanoma-induced expansion of intestinal NK cells and Th1 cells and their migration from the gut to tumor-bearing bones. Demonstrating the functional relevance of immune cell trafficking from the gut to the bone marrow (BM) in bone metastasis, blockade of S1P-mediated intestinal egress of NK and Th1 cells, or inhibition of their CXCR3/CXCL9-mediated influx into the BM, prevented the expansion of BM NK and Th1 cells and accelerated tumor growth and osteolysis. Using a mouse model, this study revealed mechanisms of microbiota-mediated gut-bone crosstalk that are relevant to the immunological restraint of melanoma metastasis and tumor growth in bone. Microbiome modifications induced by antibiotics might have negative clinical consequences in patients with melanoma.

Temporospatial regulation of intraflagellar transport is required for the endochondral ossification in mice

Ciliogenic components, such as the family of intraflagellar transport (IFT) proteins, are recognized to play key roles in endochondral ossification, a critical process to form most bones. However, the unique functions and roles of each IFT during endochondral ossification remain unclear. Here, we show that IFT20 is required for endochondral ossification in mice. Utilizing osteo-chondrocyte lineage-specific Cre mice (Prx1-Cre and Col2-Cre), we deleted Ift20 to examine its function. Although chondrocyte-specific Ift20 deletion with Col2-Cre mice did not cause any overt skeletal defects, mesoderm-specific Ift20 deletion using Prx1-Cre (Ift20:Prx1-Cre) mice resulted in shortened limb outgrowth. Primary cilia were absent on chondrocytes of Ift20:Prx1-Cre mice, and ciliary-mediated Hedgehog signaling was attenuated in Ift20:Prx1-Cre mice. Interestingly, loss of Ift20 also increased Fgf18 expression in the perichondrium that sustained Sox9 expression, thus preventing endochondral ossification. Inhibition of enhanced phospho-ERK1/2 activation partially rescued defective chondrogenesis in Ift20 mutant cells, supporting an important role for FGF signaling. Our findings demonstrate that IFT20 is a critical regulator of temporospatial FGF signaling that is required for endochondral ossification.

Do Interactions of Vitamin D3 and BMP Signaling Hold Implications in the Pathogenesis of Fibrodysplasia Ossificans Progressiva?

PURPOSE OF REVIEW

Fibrodysplasia ossificans progressiva (FOP) is a debilitating rare disease known for episodic endochondral heterotopic ossification (HO) caused by gain-of-function mutations in ACVR1/ALK2. However, disease severity varies among patients with identical mutations suggesting disease-modifying factors, including diet, may have therapeutic implications. The roles of vitamin D₃ in calcium metabolism and chondrogenesis are known, but its effects on BMP signaling and chondrogenesis are less studied. This review attempts to assess the possibility of vitamin D's effects in FOP by exploring relevant intersections of VD₃ with mechanisms of FOP flares.

RECENT FINDINGS

In vitro and in vivo studies suggest vitamin D suppresses inflammation, while clinical studies suggest that vitamin D₃ protects against arteriosclerosis and inversely correlates with non-genetic intramuscular HO. However, the enhancement of chondrogenesis, BMP signaling, and possibly Activin A expression by vitamin D may be more relevant in FOP. There appears to be little potential for vitamin D to reduce HO in FOP, but testing the potential for excess vitamin D to promote HO may be warranted.

The Role of Bone Morphogenetic Protein Signaling in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) affects over 30% of adults in the United States. Bone morphogenetic protein (BMP) signaling is known to contribute to hepatic fibrosis, but the role of BMP signaling in the development of NAFLD is unclear. In this study, treatment with either of two BMP inhibitors reduced hepatic triglyceride content in diabetic (db/db) mice. BMP inhibitor-induced decrease in hepatic triglyceride levels was associated with decreased mRNA encoding Dgat2, an enzyme integral to triglyceride synthesis. Treatment of hepatoma cells with BMP2 induced DGAT2 expression and activity via intracellular SMAD signaling. In humans we identified a rare missense single nucleotide polymorphism in the BMP type 1 receptor ALK6 (rs34970181;R371Q) associated with a 2.1-fold increase in the prevalence of NAFLD. In vitro analyses revealed R371Q:ALK6 is a previously unknown constitutively active receptor. These data show that BMP signaling is an important determinant of NAFLD in a murine model and is associated with NAFLD in humans.

Drill and Fill Technique for the Treatment of Scaphoid Delayed Unions and Nonunions

Background  This article reviews the results of a surgical technique using three iterations of drilling , autologous cancellous bone grafting ( filling ), and use of an intraosseous compression screw for the treatment of nondisplaced or minimally displaced scaphoid delayed unions or nonunions. Methods  Part 1-Cadaveric study: Three cadaveric scaphoids underwent stained cancellous bone graft packing and headless cannulated compression screw placement using a single iteration of drilling and graft packing. Three additional scaphoids were allocated to the triple "drill and fill" group, and underwent three iterations of drilling and graft packing before screw insertion. Graft particle distribution on mid-sagittal sections was assessed under fluorescence microscopy. Comparison of normalized areas between the single and triple "drill and fill" groups was performed using repeated measures ANOVA and Tukey's post hoc test. Part 2-Clinical study: Twelve patients with minimally displaced scaphoid delayed unions and nonunions treated between April 2007 and December 2013 with the triple "drill and fill" technique were included. The average follow-up was 60.4 weeks. Two fellowship-trained musculoskeletal radiologists independently reviewed images for fracture healing. Results  By the histomorphometric analysis, there was improved autograft distribution along the screw tract, particularly within the proximal pole, with three iterations of drilling and filling. Clinically, 11 of 12 delayed unions and nonunions had healed. Conclusion  Our results support the use of the "drill and fill" technique as an option for the treatment of select nondisplaced or minimally displaced scaphoid nonunions and delayed unions at the waist without avascular necrosis of the proximal pole. Level of Evidence  This is a Level IV study.

Methods for the reliable induction of heterotopic ossification in the conditional Alk2Q207D mouse

OBJECTIVES

Conditional Alk2^Q207D-floxed (caALK2^fl) mice have previously been used as a model of heterotopic ossification (HO). However, HO formation in this model can be highly variable, and it is unclear which methods reliably induce HO. Hence, these studies report validated methods for reproducibly inducing HO in caALK2^fl mice.

METHODS

Varying doses of Adex-cre and cardiotoxin (CTX) were injected into the calf muscles of 9, 14, or 28-day-old caALK2^fl/- or caALK2^fl/fl mice. HO was measured by planar radiography or microCT at 14-28 days post-injury.

RESULTS

In 9-day-old caALK2^fl/- or caALK2^fl/fl mice, single injections of 10⁹ PFU Adex-cre and 0.3 μg of CTX were sufficient to induce extensive HO within 14 days post-injury. In 28-day-old mice, the doses were increased to 5 x 10⁹ PFU Adex-cre and 3.0 μg of CTX to achieve similar consistency, but at a slower rate versus younger mice. Using a crush injury, instead of CTX, also provided consistent induction of HO. Finally, the Type 1 BMPR inhibitor, DMH1, significantly reduced HO formation in 28-day-old caALK2^fl/fl mice.

CONCLUSIONS

These data illustrate multiple methods for reliable induction of localized HO in the caALK2^flmouse that can serve as a starting point for new laboratories utilizing this model.

LNK deficiency promotes acute aortic dissection and rupture

Aortic dissection (AD) is a life-threatening vascular disease with limited treatment strategies. Here, we show that loss of the GWAS-identified SH2B3 gene, encoding lymphocyte adaptor protein LNK, markedly increases susceptibility to acute AD and rupture in response to angiotensin (Ang) II infusion. As early as day 3 following Ang II infusion, prior to the development of AD, Lnk-/- aortas display altered mechanical properties, increased elastin breaks, collagen thinning, enhanced neutrophil accumulation, and increased MMP-9 activity compared with WT mice. Adoptive transfer of Lnk-/- leukocytes into Rag1-/- mice induces AD and rupture in response to Ang II, demonstrating that LNK deficiency in hematopoietic cells plays a key role in this disease. Interestingly, treatment with doxycycline prevents the early accumulation of aortic neutrophils and significantly reduces the incidence of AD and rupture. PrediXcan analysis in a biobank of more than 23,000 individuals reveals that decreased expression of SH2B3 is significantly associated with increased frequency of AD-related phenotypes (odds ratio 0.81). Thus, we identified a role for LNK in the pathology of AD in experimental animals and humans and describe a new model that can be used to inform both inherited and acquired forms of this disease.

The proto-oncogene function of Mdm2 in bone

Mouse double minute 2 (Mdm2) is a multifaceted oncoprotein that is highly regulated with distinct domains capable of cellular transformation. Loss of Mdm2 is embryonically lethal, making it difficult to study in a mouse model without additional genetic alterations. Global overexpression through increased Mdm2 gene copy number (Mdm2^Tg ) results in the development of hematopoietic neoplasms and sarcomas in adult animals. In these mice, we found an increase in osteoblastogenesis, differentiation, and a high bone mass phenotype. Since it was difficult to discern the cell lineage that generated this phenotype, we generated osteoblast-specific Mdm2 overexpressing (Mdm2^TgOb ) mice in 2 different strains, C57BL/6 and DBA. These mice did not develop malignancies; however, these animals and the MG63 human osteosarcoma cell line with high levels of Mdm2 showed an increase in bone mineralization. Importantly, overexpression of Mdm2 corrected age-related bone loss in mice, providing a role for the proto-oncogenic activity of Mdm2 in bone health of adult animals.

Differences in sensitivity to microstructure between cyclic- and impact-based microindentation of human cortical bone

Unlike the known relationships between traditional mechanical properties and microstructural features of bone, the factors that influence the mechanical resistance of bone to cyclic reference point microindention (cRPI) and impact microindention (IMI) have yet to be identified. To determine whether cRPI and IMI properties depend on microstructure, we indented the tibia mid-shaft, the distal radius, and the proximal humerus from 10 elderly donors using the BioDent and OsteoProbe (neighboring sites). As the only output measure of IMI, bone material strength index (BMSi) was significantly different across all three anatomical sites being highest for the tibia mid-shaft and lowest for the proximal humerus. Total indentation distance (inverse of BMSi) was higher for the proximal humerus than for the tibia mid-shaft but was not different between other anatomical comparisons. As a possible explanation for the differences in BMSi, pore water, as determined by ¹ H nuclear magnetic resonance, was lowest for the tibia and highest for the humerus. Moreover, the local intra-cortical porosity, as determined by micro-computed tomography, was negatively correlated with BMSi for both arm bones. BMSi was also positively correlated with peak bending stress of cortical bone extracted from the tibia mid-shaft. Microstructural correlations with cRPI properties were not significant for any of the bones. The one exception was that average energy dissipated during cRPI was negatively correlated with local tissue mineral density in the tibia mid-shaft. With higher indentation force and larger tip diameter than cRPI, only IMI appears to be sensitive to the underlying porosity of cortical bone. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1442-1452, 2017.

Novel methods for microCT-based analyses of vasculature in the renal cortex reveal a loss of perfusable arterioles and glomeruli in eNOS-/- mice

Background

Two-dimensional measures of vascular architecture provide incomplete information about vascular structure. This study applied a novel rigorous method for 3D microCT-based analysis of total and cortical renal vasculature combined with a novel method to isolate and quantify the number of perfused glomeruli to assess vascular changes in eNOS-/- mice.

Methods

Two month old male wildtype and eNOS-/- mice were perfused with heparinized saline followed by radiopaque Microfil. The Microfil-perfused vasculature of excised kidneys was imaged by μCT with an isotropic voxel-size of 5.0 μm. For analysis of renal cortical vasculature, a custom algorithm was created to define the cortical volume of interest (VOI) as the entire volume within 600 μm of the renal surface. Vessel thickness in the whole kidney or renal cortex was analyzed by plotting the distribution of vascular volume at each measured thickness and examining differences between the genotypes at individual thicknesses. A second image processing algorithm was created to isolate, identify, and extract contrast perfused glomeruli from the cortical vessels.

Results

Fractional vascular volume (vascular volume/kidney volume; VV/KV) and Vessel Number/mm (V.N) were significantly lower in eNOS-/- mice vs. WT (p < 0.05). eNOS-/- kidneys had significantly fewer perfusable vessels vs. WT in the range of 20–40 μm in thickness. The cortex of eNOS-/- kidneys had significantly lower VV, VV/cortical volume, and V.N, with an increase in the distance between vessels (all p < 0.05). The total volume of vessels in the range of 20–30 μm was significantly lower in the cortex of eNOS-/- mice compared to WT (p < 0.05). Moreover, the total number of perfused glomeruli was significantly decreased in eNOS-/- mice (p < 0.01).

Conclusions

The methods presented here demonstrate a new method to analyze contrast enhanced μCT images for vascular phenotyping of the murine kidney. These data also demonstrate that kidneys in eNOS-/- mice have severe defects in vascular perfusion/structure in the renal cortex.

The effect of an inhibitor of gut serotonin (LP533401) during the induction of periodontal disease

BACKGROUND AND OBJECTIVE

LP533401 is an inhibitor of tryptophan hydroxylase 1, which regulates serotonin production in the gut. Previous work indicates that LP533401 has an anabolic effect in bone. Thus, we hypothesized that inhibition of gut serotonin production may modulate the host response in periodontal disease. In this study, we aimed to analyze the effects of LP533401 in a rat periodontitis model to evaluate the role of gut serotonin in periodontitis pathophysiology.

MATERIAL AND METHODS

Twenty-four rats were divided into three groups: treated group (T: ligature-induced periodontal disease and LP533401, 25 mg/kg/d) by gavage; ligature group (L: ligature-induced periodontal disease only); and control group (C: without ligature-induced periodontal disease). After 28 d, radiographic alveolar bone support was measured on digital radiographs, and alveolar bone volume fraction, tissue mineral density and trabeculae characteristics were quantified by microcomputed tomography in the right hemi-mandible. Left hemi-mandibles were decalcified and alveolar bone loss, attachment loss and area of collagen in the gingiva were histologically analyzed.

RESULTS

Significant difference between the L and C groups was found, confirming that periodontal disease was induced. We observed no difference between the T and L groups regarding alveolar bone destruction and area of collagen.

CONCLUSION

LP533401 (25 mg/kg/d) for 28 d does not prevent bone loss and does not modulate host response in a rat model of induced periodontal disease.

Inner Ear Vestibular Signals Regulate Bone Remodeling via the Sympathetic Nervous System

The inner ear vestibular system has numerous projections on central brain centers that regulate sympathetic outflow, and skeletal sympathetic projections affect bone remodeling by inhibiting bone formation by osteoblasts and promoting bone resorption by osteoclasts. In this study, we show that bilateral vestibular lesions in mice cause a low bone mass phenotype associated with decreased bone formation and increased bone resorption. This reduction in bone mass is most pronounced in lower limbs, is not associated with reduced locomotor activity or chronic inflammation, and could be prevented by the administration of the β-blocker propranolol and by genetic deletion of the β2-adrenergic receptor, globally or specifically in osteoblasts. These results provide novel experimental evidence supporting a functional autonomic link between central proprioceptive vestibular structures and the skeleton. Because vestibular dysfunction often affects the elderly, these results also suggest that age-related bone loss might have a vestibular component and that patients with inner ear pathologies might be at risk for fracture. Lastly, these data might have relevance to the bone loss observed in microgravity, as vestibular function is altered in this condition as well. © 2015 American Society for Bone and Mineral Research.

Predicting mouse vertebra strength with micro-computed tomography-derived finite element analysis

As in clinical studies, finite element analysis (FEA) developed from computed tomography (CT) images of bones are useful in pre-clinical rodent studies assessing treatment effects on vertebral body (VB) strength. Since strength predictions from microCT-derived FEAs (μFEA) have not been validated against experimental measurements of mouse VB strength, a parametric analysis exploring material and failure definitions was performed to determine whether elastic μFEAs with linear failure criteria could reasonably assess VB strength in two studies, treatment and genetic, with differences in bone volume fraction between the control and the experimental groups. VBs were scanned with a 12-μm voxel size, and voxels were directly converted to 8-node, hexahedral elements. The coefficient of determination or R (2) between predicted VB strength and experimental VB strength, as determined from compression tests, was 62.3% for the treatment study and 85.3% for the genetic study when using a homogenous tissue modulus (E t) of 18 GPa for all elements, a failure volume of 2%, and an equivalent failure strain of 0.007. The difference between prediction and measurement (that is, error) increased when lowering the failure volume to 0.1% or increasing it to 4%. Using inhomogeneous tissue density-specific moduli improved the R (2) between predicted and experimental strength when compared with uniform E t=18 GPa. Also, the optimum failure volume is higher for the inhomogeneous than for the homogeneous material definition. Regardless of model assumptions, μFEA can assess differences in murine VB strength between experimental groups when the expected difference in strength is at least 20%.

Combined MEK inhibition and BMP2 treatment promotes osteoblast differentiation and bone healing in Nf1Osx -/- mice

Neurofibromatosis type I (NF1) is an autosomal dominant disease with an incidence of 1/3000, caused by mutations in the NF1 gene, which encodes the RAS/GTPase-activating protein neurofibromin. Non-bone union after fracture (pseudarthrosis) in children with NF1 remains a challenging orthopedic condition to treat. Recent progress in understanding the biology of neurofibromin suggested that NF1 pseudarthrosis stems primarily from defects in the bone mesenchymal lineage and hypersensitivity of hematopoietic cells to TGFβ. However, clinically relevant pharmacological approaches to augment bone union in these patients remain limited. In this study, we report the generation of a novel conditional mutant mouse line used to model NF1 pseudoarthrosis, in which Nf1 can be ablated in an inducible fashion in osteoprogenitors of postnatal mice, thus circumventing the dwarfism associated with previous mouse models where Nf1 is ablated in embryonic mesenchymal cell lineages. An ex vivo-based cell culture approach based on the use of Nf1(flox/flox) bone marrow stromal cells showed that loss of Nf1 impairs osteoprogenitor cell differentiation in a cell-autonomous manner, independent of developmental growth plate-derived or paracrine/hormonal influences. In addition, in vitro gene expression and differentiation assays indicated that chronic ERK activation in Nf1-deficient osteoprogenitors blunts the pro-osteogenic property of BMP2, based on the observation that only combination treatment with BMP2 and MEK inhibition promoted the differentiation of Nf1-deficient osteoprogenitors. The in vivo preclinical relevance of these findings was confirmed by the improved bone healing and callus strength observed in Nf1osx (-/-) mice receiving Trametinib (a MEK inhibitor) and BMP2 released locally at the fracture site via a novel nanoparticle and polyglycidol-based delivery method. Collectively, these results provide novel evidence for a cell-autonomous role of neurofibromin in osteoprogenitor cells and insights about a novel targeted approach for the treatment of NF1 pseudoarthrosis.

Asfotase-α improves bone growth, mineralization and strength in mouse models of neurofibromatosis type-1

Mineralization of the skeleton depends on the balance between levels of pyrophosphate (PPi), an inhibitor of hydroxyapatite formation, and phosphate generated from PPi breakdown by alkaline phosphatase (ALP). We report here that ablation of Nf1, encoding the RAS/GTPase–activating protein neurofibromin, in bone–forming cells leads to supraphysiologic PPi accumulation, caused by a chronic ERK–dependent increase in genes promoting PPi synthesis and extracellular transport, namely Enpp1 and Ank. It also prevents BMP2–induced osteoprogenitor differentiation and, consequently, expression of ALP and PPi breakdown, further contributing to PPi accumulation. The short stature, impaired bone mineralization and strength in mice lacking Nf1 in osteochondroprogenitors or osteoblasts could be corrected by enzyme therapy aimed at reducing PPi concentration. These results establish neurofibromin as an essential regulator of bone mineralization, suggest that altered PPi homeostasis contributes to the skeletal dysplasiae associated with neurofibromatosis type-1 (NF1), and that some of the NF1 skeletal conditions might be preventable pharmacologically.

Development of Raman spectral markers to assess metastatic bone in breast cancer

Bone is the most common site for breast cancer metastases. One of the major complications of bone metastasis is pathological bone fracture caused by chronic bone loss and degeneration. Current guidelines for the prediction of pathological fracture mainly rely on radiographs or computed tomography, which are limited in their ability to predict fracture risk. The present study explored the feasibility of using Raman spectroscopy to estimate pathological fracture risk by characterizing the alterations in the compositional properties of metastatic bones. Tibiae with evident bone destruction were investigated using Raman spectroscopy. The carbonation level calculated by the ratio of carbonate/phosphate ν1 significantly increased in the tumor-bearing bone at all the sampling regions at the proximal metaphysis and diaphysis, while tumor-induced elevation in mineralization and crystallinity was more pronounced in the metaphysis. Furthermore, the increased carbonation level is positively correlated to bone lesion size, indicating that this parameter could serve as a unique spectral marker for tumor progression and bone loss. With the promising advances in the development of spatially offset Raman spectroscopy for deep tissue measurement, this spectral marker can potentially be used for future noninvasive evaluation of metastatic bone and prediction of pathological fracture risk.

A secreted bacterial protease tailors the Staphylococcus aureus virulence repertoire to modulate bone remodeling during osteomyelitis

Osteomyelitis is a common manifestation of invasive Staphylococcus aureus infection. Pathogen-induced bone destruction limits antimicrobial penetration to the infectious focus and compromises treatment of osteomyelitis. To investigate mechanisms of S. aureus-induced bone destruction, we developed a murine model of osteomyelitis. Microcomputed tomography of infected femurs revealed that S. aureus triggers profound alterations in bone turnover. The bacterial regulatory locus sae was found to be critical for osteomyelitis pathogenesis, as Sae-regulated factors promote pathologic bone remodeling and intraosseous bacterial survival. Exoproteome analyses revealed the Sae-regulated protease aureolysin as a major determinant of the S. aureus secretome and identified the phenol-soluble modulins as aureolysin-degraded, osteolytic peptides that trigger osteoblast cell death and bone destruction. These studies establish a murine model for pathogen-induced bone remodeling, define Sae as critical for osteomyelitis pathogenesis, and identify protease-dependent exoproteome remodeling as a major determinant of the staphylococcal virulence repertoire.

Prostate cancer metastases alter bone mineral and matrix composition independent of effects on bone architecture in mice--a quantitative study using microCT and Raman spectroscopy

Prostate cancer is the most common primary tumor and the second leading cause of cancer-related deaths in men in the United States. Prostate cancer bone metastases are characterized by abnormal bone remodeling processes and result in a variety of skeletal morbidities. Prevention of skeletal complications is a crucial element in prostate cancer management. This study investigated prostate cancer-induced alterations in the molecular composition and morphological structure of metastasis-bearing bones in a mouse model of prostate cancer using Raman spectroscopy and micro-computed tomography (microCT). LNCaP C4-2B prostate cancer cells were injected into the right tibiae of 5-week old male SCID mice. Upon sacrifice at 8weeks post tumor inoculation, two out of the ten tumor-bearing tibiae showed only osteoblastic lesions in the radiographs, 4 osteolytic lesions only and 4 mixed with osteoblastic and osteolytic lesions. Carbonate substitution was significantly increased while there was a marked reduction in the level of collagen mineralization, mineral crystallinity, and carbonate:matrix ratio in the cortex of the intact tumor-bearing tibiae compared to contralateral controls. MicroCT analysis revealed a significant reduction in bone volume/total volume, trabecular number and trabecular thickness, as well as significant increase in bone surface/volume ratio in tibiae with osteolytic lesions, suggesting active bone remodeling and bone loss. None of the changes in bone compositional properties were correlated with lesion area from radiographs or the changes in bone architecture from microCT. This study indicates that LNCaP C4-2B prostate cancer metastases alter bone tissue composition independent of changes in architecture, and altered bone quality may be an important contributor to fracture risk in these patients. Raman spectroscopy may provide a new avenue of investigation into interactions between tumor and bone microenvironment.

Percutaneous injection of augment injectable bone graft (rhPDGF-BB and β-tricalcium phosphate [β-TCP]/bovine type I collagen matrix) increases vertebral bone mineral density in geriatric female baboons

BACKGROUND CONTEXT

Recombinant human platelet-derived growth factor-BB (rhPDGF-BB) homodimer is a chemotactic, mitogenic, and angiogenic factor expressed by platelets. This biological triad is profoundly important in the bone regenerative cascade. Therefore, the expectation was that rhPDGF-BB locally administered to designated lumbar vertebrae in a soluble Type I bovine collagen/β-tricalcium phosphate (β-TCP) injectable paste would have an osteoanabolic effect.

PURPOSE

The study objective focused on safety and efficacy of the rhPDGF-BB and soluble Type I bovine collagen/β-TCP to increase bone density when injected directly into specific lumbar vertebral bodies in elderly (17- to 18-year-old) female baboons.

STUDY DESIGN/SETTING

The study was designed to determine whether vertebral bone mineral density (BMD) in aged female baboons could be increased by locally administering recombinant rhPDGF-BB combined in a soluble Type I bovine collagen/β-TCP paste formulation.

METHODS

A total of six baboons were divided equally into two groups. Group 1 received 1.0 mg/mL rhPDGF-BB in 20 mM sodium acetate plus soluble Type I bovine collagen/β-TCP. Group 2 was treated with 20 mM sodium acetate plus soluble Type I bovine collagen/β-TCP. Baboons in each group also received a sham surgery. Surgery was conducted using a percutaneous, fluoroscopically guided approach, and quantitative computed tomography (qCT) and radiographs were done at dedicated time periods. The qCT was used to determine volumetric BMD (vBMD). At euthanasia (36-week posttreatment), lumbar vertebrae were recovered and analyzed by qCT scans and histology. Funds were received to support this work from BioMimetic Therapeutics, Inc. The device that is the subject of this manuscript is not Food Drug Administration approved for this indication and is not commercially available in the United States.

RESULTS

The qCT and histopathological data suggested that vBMD and bone morphology increased significantly in the lumbar vertebrae treated with the rhPDGF-BB-containing composition.

CONCLUSIONS

Bone mineral density and bone morphology quality of lumbar vertebrae in aged female baboons were improved by direct injection of rhPDGF-BB in a soluble Type I bovine collagen/β-TCP paste. Throughout the course of the study, there were neither local nor systemic adverse effects.

Silent information regulator (Sir)T1 inhibits NF-κB signaling to maintain normal skeletal remodeling

Silent information regulator T1 (SirT1) is linked to longevity and negatively controls NF-κB signaling, a crucial mediator of survival and regulator of both osteoclasts and osteoblasts. Here we show that NF-κB repression by SirT1 in both osteoclasts and osteoblasts is necessary for proper bone remodeling and may contribute to the mechanisms linking aging and bone loss. Osteoclast- or osteoblast-specific SirT1 deletion using the Sirt(flox/flox) mice crossed to lysozyme M-cre and the 2.3 kb col1a1-cre transgenic mice, respectively, resulted in decreased bone mass caused by increased resorption and reduced bone formation. In osteoclasts, lack of SirT1 promoted osteoclastogenesis in vitro and activated NF-κB by increasing acetylation of Lysine 310. Importantly, this increase in osteoclastogenesis was blocked by pharmacological inhibition of NF-κB. In osteoblasts, decreased SirT1 reduced osteoblast differentiation, which could also be rescued by inhibition of NF-κB. In further support of the critical role of NF-κB signaling in bone remodeling, elevated NF-κB activity in IκBα(+/-) mice uncoupled bone resorption and formation, leading to reduced bone mass. These findings support the notion that SirT1 is a genetic determinant of bone mass, acting in a cell-autonomous manner in both osteoblasts and osteoclasts, through control of NF-κB and bone cell differentiation.

Stimulation of host bone marrow stromal cells by sympathetic nerves promotes breast cancer bone metastasis in mice

The activation of sympathetic nerves by psychosocial stress creates a favorable environment in bone for the establishment of cancer cells in a mouse model of breast cancer.

Bone and lung metastases are responsible for the majority of deaths in patients with breast cancer. Following treatment of the primary cancer, emotional and psychosocial factors within this population precipitate time to recurrence and death, however the underlying mechanism(s) remain unclear. Using a mouse model of bone metastasis, we provide experimental evidence that activation of the sympathetic nervous system, which is one of many pathophysiological consequences of severe stress and depression, promotes MDA-231 breast cancer cell colonization of bone via a neurohormonal effect on the host bone marrow stroma. We demonstrate that induction of RANKL expression in bone marrow osteoblasts, following β2AR stimulation, increases the migration of metastatic MDA-231 cells in vitro, independently of SDF1-CXCR4 signaling. We also show that the stimulatory effect of endogenous (chronic stress) or pharmacologic sympathetic activation on breast cancer bone metastasis in vivo can be blocked with the β-blocker propranolol, and by knockdown of RANK expression in MDA-231 cells. These findings indicate that RANKL promotes breast cancer cell metastasis to bone via its pro-migratory effect on breast cancer cells, independently of its effect on bone turnover. The emerging clinical implication, supported by recent epidemiological studies, is that βAR-blockers and drugs interfering with RANKL signaling, such as Denosumab, could increase patient survival if used as adjuvant therapy to inhibit both the early colonization of bone by metastatic breast cancer cells and the initiation of the “vicious cycle” of bone destruction induced by these cells.

Improved detection programs and better drugs to eradicate breast tumors have increased survival in women with breast cancer. However, pain and metastasis to distant organs, including bone, remain significant clinical problems. Understanding why and how metastatic cancer cells colonize specific organs is therefore critical if we are to further improve morbidity and mortality for these patients. Using a mouse model of breast cancer bone metastasis, we present evidence that activation of sympathetic nerves, which is typical in chronic stress or depression, promotes the colonization and establishment of metastatic cancer cells within the bone marrow, leading to an increase in bone osteolytic lesions. We show that this effect is mediated via a β-adrenergic receptor-dependent response of the host bone marrow stroma to catecholamines, that are released upon sympathetic activation, and via the pro-migratory activity of RANKL, a cytokine that is well known to promote bone resorption. Of importance clinically, blocking sympathetic activation with a β-blocker, or blocking RANKL signaling in cancer cells, inhibited the stimulatory effect of sympathetic activation on bone metastasis in this mouse model. Stress-induced sympathetic activation may thus explain, at least in part, the reduced survival rate of breast cancer patients experiencing severe depression. The data also support the use of β-blockers or RANKL blockade as possible adjuvant therapy for women with breast cancer.

Inhibin A enhances bone formation during distraction osteogenesis

Given the aging population and the increased incidence of fracture in the elderly population, the need exists for agents that can enhance bone healing, particularly in situations of delayed fracture healing and/or non-union. Our previous studies demonstrated that overexpression of the gonadal peptide, human inhibin A (hInhA), in transgenic mice enhances bone formation and strength via increased osteoblast activity. We tested the hypothesis that hInhA can also exert anabolic effects in a murine model of distraction osteogenesis (DO), using both transgenic hInhA overexpression and administration of normal physiological levels of hInhA in adult male Swiss-Webster mice. Tibial osteotomies and external ring fixation were performed, followed by a 3-day latency period, 14-day distraction, and sacrifice on day 18. Supraphysiological levels of hInhA in transgenic mice, but not normal physiological levels of hInhA, significantly increased endosteal bone formation and mineralized bone area in the distraction gap, as determined by radiographic and µCT analysis. Significantly, increased PCNA and osteocalcin expression in the primary matrix front suggested that hInhA increased osteoblast proliferation. This mechanism is consistent with the effects of other agents and pathologies that modulate bone formation during DO, and demonstrates the potential of hInhA to enhance bone repair and regeneration.

Cytoskeletal defects in Bmpr2-associated pulmonary arterial hypertension

The heritable form of pulmonary arterial hypertension (PAH) is typically caused by a mutation in bone morphogenic protein receptor type 2 (BMPR2), and mice expressing Bmpr2 mutations develop PAH with features similar to human disease. BMPR2 is known to interact with the cytoskeleton, and human array studies in PAH patients confirm alterations in cytoskeletal pathways. The goal of this study was to evaluate cytoskeletal defects in BMPR2-associated PAH. Expression arrays on our Bmpr2 mutant mouse lungs revealed cytoskeletal defects as a prominent molecular consequence of universal expression of a Bmpr2 mutation (Rosa26-Bmpr2(R899X)). Pulmonary microvascular endothelial cells cultured from these mice have histological and functional cytoskeletal defects. Stable transfection of different BMPR2 mutations into pulmonary microvascular endothelial cells revealed that cytoskeletal defects are common to multiple BMPR2 mutations and are associated with activation of the Rho GTPase, Rac1. Rac1 defects are corrected in cell culture and in vivo through administration of exogenous recombinant human angiotensin-converting enzyme 2 (rhACE2). rhACE2 reverses 77% of gene expression changes in Rosa26-Bmpr2(R899X) transgenic mice, in particular, correcting defects in cytoskeletal function. Administration of rhACE2 to Rosa26-Bmpr2(R899X) mice with established PAH normalizes pulmonary pressures. Together, these findings suggest that cytoskeletal function is central to the development of BMPR2-associated PAH and that intervention against cytoskeletal defects may reverse established disease.

Anti-transforming growth factor ß antibody treatment rescues bone loss and prevents breast cancer metastasis to bone

Breast cancer often metastasizes to bone causing osteolytic bone resorption which releases active TGFβ. Because TGFβ favors progression of breast cancer metastasis to bone, we hypothesized that treatment using anti-TGFβ antibody may reduce tumor burden and rescue tumor-associated bone loss in metastatic breast cancer. In this study we have tested the efficacy of an anti-TGFβ antibody 1D11 preventing breast cancer bone metastasis. We have used two preclinical breast cancer bone metastasis models, in which either human breast cancer cells or murine mammary tumor cells were injected in host mice via left cardiac ventricle. Using several in vivo, in vitro and ex vivo assays, we have demonstrated that anti-TGFβ antibody treatment have significantly reduced tumor burden in the bone along with a statistically significant threefold reduction in osteolytic lesion number and tenfold reduction in osteolytic lesion area. A decrease in osteoclast numbers (p = 0.027) in vivo and osteoclastogenesis ex vivo were also observed. Most importantly, in tumor-bearing mice, anti-TGFβ treatment resulted in a twofold increase in bone volume (p<0.01). In addition, treatment with anti-TGFβ antibody increased the mineral-to-collagen ratio in vivo, a reflection of improved tissue level properties. Moreover, anti-TGFβ antibody directly increased mineralized matrix formation in calverial osteoblast (p = 0.005), suggesting a direct beneficial role of anti-TGFβ antibody treatment on osteoblasts. Data presented here demonstrate that anti-TGFβ treatment may offer a novel therapeutic option for tumor-induced bone disease and has the dual potential for simultaneously decreasing tumor burden and rescue bone loss in breast cancer to bone metastases. This approach of intervention has the potential to reduce skeletal related events (SREs) in breast cancer survivors.

Physiologically relevant oxidative degradation of oligo(proline) cross-linked polymeric scaffolds

Chronic inflammation-mediated oxidative stress is a common mechanism of implant rejection and failure. Therefore, polymer scaffolds that can degrade slowly in response to this environment may provide a viable platform for implant site-specific, sustained release of immunomodulatory agents over a long time period. In this work, proline oligomers of varying lengths (P(n)) were synthesized and exposed to oxidative environments, and their accelerated degradation under oxidative conditions was verified via high performance liquid chromatography and gel permeation chromatography. Next, diblock copolymers of poly(ethylene glycol) (PEG) and poly(ε-caprolactone) (PCL) were carboxylated to form 100 kDa terpolymers of 4%PEG-86%PCL-10%cPCL (cPCL = poly(carboxyl-ε-caprolactone); i% indicates molar ratio). The polymers were then cross-linked with biaminated PEG-P(n)-PEG chains, where P(n) indicates the length of the proline oligomer flanked by PEG chains. Salt-leaching of the polymeric matrices created scaffolds of macroporous and microporous architecture, as observed by scanning electron microscopy. The degradation of scaffolds was accelerated under oxidative conditions, as evidenced by mass loss and differential scanning calorimetry measurements. Immortalized murine bone-marrow-derived macrophages were then seeded on the scaffolds and activated through the addition of γ-interferon and lipopolysaccharide throughout the 9-day study period. This treatment promoted the release of H(2)O(2) by the macrophages and the degradation of proline-containing scaffolds compared to the control scaffolds. The accelerated degradation was evidenced by increased scaffold porosity, as visualized through scanning electron microscopy and X-ray microtomography imaging. The current study provides insight into the development of scaffolds that respond to oxidative environments through gradual degradation for the controlled release of therapeutics targeted to diseases that feature chronic inflammation and oxidative stress.

Differential effects between the loss of MMP-2 and MMP-9 on structural and tissue-level properties of bone

Matrix metalloproteinases (MMPs) are capable of processing certain components of bone tissue, including type 1 collagen, a determinant of the biomechanical properties of bone tissue, and they are expressed by osteoclasts and osteoblasts. Therefore, we posit that MMP activity can affect the ability of bone to resist fracture. To explore this possibility, we determined the architectural, compositional, and biomechanical properties of bones from wild-type (WT), Mmp2(-/-) , and Mmp9(-/-) female mice at 16 weeks of age. MMP-2 and MMP-9 have similar substrates but are expressed primarily by osteoblasts and osteoclasts, respectively. Analysis of the trabecular compartment of the tibia metaphysis by micro-computed tomography (µCT) revealed that these MMPs influence trabecular architecture, not volume. Interestingly, the loss of MMP-9 improved the connectivity density of the trabeculae, whereas the loss of MMP-2 reduced this parameter. Similar differential effects in architecture were observed in the L(5) vertebra, but bone volume fraction was lower for both Mmp2(-/-) and Mmp9(-/-) mice than for WT mice. The mineralization density and mineral-to-collagen ratio, as determined by µCT and Raman microspectroscopy, were lower in the Mmp2(-/-) bones than in WT control bones. Whole-bone strength, as determined by three-point bending or compression testing, and tissue-level modulus and hardness, as determined by nanoindentation, were less for Mmp2(-/-) than for WT bones. In contrast, the Mmp9(-/-) femurs were less tough with lower postyield deflection (more brittle) than the WT femurs. Taken together, this information reveals that MMPs play a complex role in maintaining bone integrity, with the cell type that expresses the MMP likely being a contributing factor to how the enzyme affects bone quality.

Defects in hepatic Notch signaling result in disruption of the communicating intrahepatic bile duct network in mice

Abnormal Notch signaling in humans results in Alagille syndrome, a pleiotropic disease characterized by a paucity of intrahepatic bile ducts (IHBDs). It is not clear how IHBD paucity develops as a consequence of atypical Notch signaling, whether by a developmental lack of bile duct formation, a post-natal lack of branching and elongation or an inability to maintain formed ducts. Previous studies have focused on the role of Notch in IHBD development, and demonstrated a dosage requirement of Notch signaling for proper IHBD formation. In this study, we use resin casting and X-ray microtomography (microCT) analysis to address the role of Notch signaling in the maintenance of formed IHBDs upon chronic loss or gain of Notch function. Our data show that constitutive expression of the Notch1 intracellular domain in bi-potential hepatoblast progenitor cells (BHPCs) results in increased IHBD branches at post-natal day 60 (P60), which are maintained at P90 and P120. By contrast, loss of Notch signaling via BHPC-specific deletion of RBP-J (RBP KO), the DNA-binding partner for all Notch receptors, results in progressive loss of intact IHBD branches with age. Interestingly, in RBP KO mice, we observed a reduction in bile ducts per portal vein at P60; no further reduction had occurred at P120. Thus, bile duct structures are not lost with age; instead, we propose a model in which BHPC-specific loss of Notch signaling results in an initial developmental defect resulting in fewer bile ducts being formed, and in an acquired post-natal defect in the maintenance of intact IHBD architecture as a result of irresolvable cholestasis. Our studies reveal a previously unappreciated role for Notch signaling in the post-natal maintenance of an intact communicating IHBD structure, and suggest that liver defects observed in Alagille syndrome patients might be more complex than bile duct paucity.

Synthesis, characterization, and remodeling of weight-bearing allograft bone/polyurethane composites in the rabbit

The process of bone healing requires the restoration of both anatomy and physiology, and there is a recognized need for innovative biomaterials that facilitate remodeling throughout this complex process. While porous scaffolds with a high degree of interconnectivity are known to accelerate cellular infiltration and new bone formation, the presence of pores significantly diminishes the initial mechanical properties of the materials, rendering them largely unsuitable for load-bearing applications. In this study, a family of non-porous composites has been fabricated by reactive compression molding of mineralized allograft bone particles (MBPs) with a biodegradable polyurethane (PUR) binder, which is synthesized from a polyester polyol and a lysine-derived polyisocyanate. At volume fractions exceeding the random close-packing limit, the particulated allograft component presented a nearly continuous osteoconductive pathway for cells into the interior of the implant. By varying the molecular weight of the polyol and manipulating the surface chemistry of the MBP via surface demineralization, compressive modulus and strength values of 3-6 GPa and 107-172 MPa were achieved, respectively. When implanted in bilateral femoral condyle plug defects in New Zealand White rabbits, MBP/PUR composites exhibited resorption of the allograft and polymer components, extensive cellular infiltration deep into the interior of the implant, and new bone formation at 6 weeks. While later in vivo timepoints are necessary to determine the ultimate fate of the MBP/PUR composites, these observations suggest that allograft bone/polymer composites have potential for future development as weight-bearing devices for orthopedic applications.

Bone turnover across the menopause transition : The role of gonadal inhibins

Accumulating evidence demonstrates increasing bone turnover and bone loss in women prior to menopause and decreases in serum estradiol levels. Increased follicle-stimulating hormone levels have been correlated with some of these peri-menopausal changes. However, decreases in gonadal inhibins of the transforming growth factor (TGF)-beta superfamily strongly correlate with increases in bone formation and resorption markers across the menopause transition and predict lumbar bone mass in peri-menopausal women, likely as a result of direct inhibin suppression of osteoblastogenesis and osteoclastogenesis. Inhibins bind specifically to cells during osteoblastogenesis and osteoclastogenesis. They can block bone morphogenetic protein (BMP)-stimulated osteoblast and osteoclast development as well as BMP-stimulated SMAD1 phosphorylation, likely via inhibin-beta-glycan sequestration of BMP Type II receptor (BMPRII). Interestingly, continuous in vivo exposure to inhibin A is anabolic and protective against gonadectomy-induced bone loss in mice, suggesting that inhibins contribute to the endocrine regulation of bone metabolism via a bimodal mechanism of action whereby cycling inhibin exposure suppresses bone turnover and continuous exposure to inhibins is anabolic.

Atf4 regulates chondrocyte proliferation and differentiation during endochondral ossification by activating Ihh transcription

Activating transcription factor 4 (Atf4) is a leucine-zipper-containing protein of the cAMP response element-binding protein (CREB) family. Ablation of Atf4 (Atf4(-/-)) in mice leads to severe skeletal defects, including delayed ossification and low bone mass, short stature and short limbs. Atf4 is expressed in proliferative and prehypertrophic growth plate chondrocytes, suggesting an autonomous function of Atf4 in chondrocytes during endochondral ossification. In Atf4(-/-) growth plate, the typical columnar structure of proliferative chondrocytes is disturbed. The proliferative zone is shortened, whereas the hypertrophic zone is transiently expanded. The expression of Indian hedgehog (Ihh) is markedly decreased, whereas the expression of other chondrocyte marker genes, such as type II collagen (Col2a1), PTH/PTHrP receptor (Pth1r) and type X collagen (Col10a1), is normal. Furthermore, forced expression of Atf4 in chondrocytes induces endogenous Ihh mRNA, and Atf4 directly binds to the Ihh promoter and activates its transcription. Supporting these findings, reactivation of Hh signaling pharmacologically in mouse limb explants corrects the Atf4(-/-) chondrocyte proliferation and short limb phenotypes. This study thus identifies Atf4 as a novel transcriptional activator of Ihh in chondrocytes that paces longitudinal bone growth by controlling growth plate chondrocyte proliferation and differentiation.

Regulation of osteoblastogenesis and osteoclastogenesis by the other reproductive hormones, Activin and Inhibin

There is both cellular and physiological evidence demonstrating that both Activins and Inhibins regulate osteoblastogenesis and osteoclastogenesis, and regulate bone mass in vivo. Although Activins and Inhibins were initially isolated from the gonad, Activins are also produced and stored in bone, whereas Inhibins exert their regulation on bone cell differentiation and metabolism via endocrine effects. The accumulating data provide evidence that reproductive hormones, distinct from classical sex steroids, are important regulators of bone mass and bone strength. Given the well described dominant antagonism of Inhibin over Activin, as well as over BMPs and TGFbeta, the gonadally derived Inhibins are important regulators of locally produced osteotrophic factors. Thus, the cycling Inhibins in females and diurnal changes in Inhibin B in males elicit temporal shifts in Inhibin levels (tone) that de-repress the pituitary. This fundamental action has the potential to de-repress locally stimulated changes in osteoblastogenesis and osteoclastogenesis, thereby altering bone metabolism.

Runt-related transcription factor 2 (RUNX2) and RUNX2-related osteogenic genes are down-regulated throughout osteogenesis in type 1 diabetes mellitus

Type 1 diabetes mellitus is associated with a number of disorders of skeletal health, conditions that rely, in part, on dynamic bone formation. A mouse model of distraction osteogenesis was used to study the consequences of streptozotocin-induced diabetes and insulin treatment on bone formation and osteoblastogenesis. In diabetic mice compared with control mice, new bone formation was decreased, and adipogenesis was increased in and around, respectively, the distraction gaps. Although insulin treatment restored bone formation to levels observed in nondiabetic control mice, it failed to significantly decrease adipogenesis. Molecular events altered during de novo bone formation in untreated type 1 diabetes mellitus, yet restored with insulin treatment were examined so as to clarify specific osteogenic genes that may contribute to diabetic bone disease. RNA from distraction gaps was analyzed by gene microarray and quantitative RT-PCR for osteogenic genes of interest. Runt-related transcription factor 2 (RUNX2), and several RUNX2 target genes, including matrix metalloproteinase-9, Akp2, integrin binding sialoprotein, Dmp1, Col1a2, Phex, Vdr, osteocalcin, and osterix, were all significantly down-regulated in the insulin-deficient, hyperglycemic diabetic animals; however, insulin treatment of diabetic animals significantly restored their expression. Expression of bone morphogenic protein-2, transcriptional coactivator with PDZ-binding motif, and TWIST2, all important regulators of RUNX2, were not impacted by the diabetic condition, suggesting that the defect in osteogenesis resides at the level of RUNX2 expression and its activity. Together, these data demonstrate that insulin and/or glycemic status can regulate osteogenesis in vivo, and systemic insulin therapy can, in large part, rescue the diabetic bone phenotype at the tissue and molecular level.

Inhibin A is an endocrine stimulator of bone mass and strength

Gonadal function plays a major role in bone homeostasis. It is widely held that the skeletal consequences of hypogonadism are solely due to a loss of sex steroids; however, increases in bone turnover begin during perimenopause before decreases in serum estradiol levels. These data and our demonstration that inhibins acutely regulate bone cell differentiation in vitro led us to test whether inhibin A (InhA) regulates bone mass in vivo. Using a transgenic model of inducible human InhA expression, InhA increased total body bone mineral density, increased bone volume, and improved biomechanical properties at the proximal tibia in intact mice and also prevented the loss of BMD and bone volume and strength associated with gonadectomy at both the spine and proximal tibia. In addition, InhA increased mineral apposition rate, double-labeled surface, and serum osteocalcin levels in vivo and osteoblastogenesis ex vivo without affecting osteoclast number or activity. Together these results demonstrate novel stimulatory effects of InhA on the skeleton in vivo. These studies provide in vivo evidence demonstrating that gonadal factors other than sex steroids play an important role in regulating bone mass and strength and, combined with our previous clinical data, suggest that gonadal InhA may be a component of the normal endocrine repertoire that regulates bone quality in both the axial and appendicular skeleton.

Chronic ethanol exposure inhibits distraction osteogenesis in a mouse model: role of the TNF signaling axis

Tumor necrosis factor-alpha (TNF-alpha) is an inflammatory cytokine that modulates osteoblastogenesis. In addition, the demonstrated inhibitory effects of chronic ethanol exposure on direct bone formation in rats are hypothetically mediated by TNF-alpha signaling. The effects in mice are unreported. Therefore, we hypothesized that in mice (1) administration of a soluble TNF receptor 1 derivative (sTNF-R1) would protect direct bone formation during chronic ethanol exposure, and (2) administration of recombinant mouse TNF-alpha (rmTNF-alpha) to ethanol naïve mice would inhibit direct bone formation. We utilized a unique model of limb lengthening (distraction osteogenesis, DO) combined with liquid diets to measure chronic ethanol's effects on direct bone formation. Chronic ethanol exposure resulted in increased marrow TNF, IL-1, and CYP 2E1 RNA levels in ethanol-treated vs. control mice, while no significant weight differences were noted. Systemic administration of sTNF-R1 during DO (8.0 mg/kg/2 days) to chronic ethanol-exposed mice resulted in enhanced direct bone formation as measured radiologically and histologically. Systemic rmTNF-alpha (10 microg/kg/day) administration decreased direct bone formation measures, while no significant weight differences were noted. We conclude that chronic ethanol-associated inhibition of direct bone formation is mediated to a significant extent by the TNF signaling axis in a mouse model.

A novel rat model for the study of deficits in bone formation in type-2 diabetes

BACKGROUND

There is evidence to suggest that impairment in bone formation and/or turnover is associated with the metabolic abnormalities characteristic of type-2 diabetes mellitus. However, bone regeneration/repair in type-2 diabetes has not been modeled. Using Zucker Diabetic Fatty (ZDF) rats (a model of type-2 diabetes) for tibial distraction osteogenesis (DO), we hypothesized that bone formation within the distraction gap would be impaired.

ANIMALS AND METHODS

Rats were examined for body weight, glycosuria, and glycosemia to confirm the diabetic condition during the study. The rats received placement of the external fixators and osteotomies on the left tibia. Distraction was initiated the following day at 0.2 mm twice a day and continued for 14 days. The lengthened tibiae were harvested and distraction gaps were examined radiographically and histologically.

RESULTS

We found significant reduction in new bone formation in the distraction gaps of the ZDF rats, both radiographically and histologically, compared to lean rats. We found a decrease in a marker of cellular proliferation in the distraction gaps and increased adipose volume in adjacent bone marrow of the ZDF rats.

INTERPRETATION

Our findings suggest that this model might be used to study the contributions of leptin resistance, insulin resistance and/or hyperglycemia to impaired osteoblastogenesis in vivo.

Aging alters the skeletal response to disuse in the rat

Disuse has been shown to cause a rapid and dramatic loss of skeletal mass and strength in the load-bearing bones of young and mature animals and humans. However, little is known about the skeletal effects of disuse in aged mammals. The present study was designed to determine whether the skeletal effects of disuse are maintained with extreme age. Fischer 344/Brown Norway male rats (6 and 32 mo old) were hindlimb suspended (HS) or housed individually for 2 wk. Trabecular volume and microarchitecture in the proximal tibia were significantly decreased by HS only in young rats. HS significantly reduced cortical bone mineral density and increased cortical porosity only in old rats by inducing new pore formation. Cortical pore diameter was also increased in old rats, regardless of loading condition. Ex vivo osteogenic and adipogenic cultures established from each group demonstrated that age and HS decreased osteoblastogenesis. Age, but not HS, decreased sensitivity to endogenous bone morphogenetic protein stimulation, as measured by treatment with exogenous Noggin. Adipocyte development increased with age, whereas HS suppressed sensitivity to peroxisome proliferator-activated receptor-gamma-induced differentiation. Serum insulin-like growth factor I levels were reduced with HS in young rats and with age in control and HS rats. These results suggest that the site of bone loss due to disuse is altered with age and that the loss of osteogenic potential with disuse in the old rats may be due to the combined effects of decreased insulin-like growth factor I levels and sensitivity, as well as diminished bone morphogenetic protein production.

Effects of systemic and local administration of recombinant human IGF-I (rhIGF-I) on de novo bone formation in an aged mouse model

DO was used in an aged mouse model to determine if systemically and/or locally administered rhIGF-I improved osteoblastogenesis and new bone formation. Local and systemic rhIGF-I treatment increased new bone formation. However, only systemic delivery produced measurable concentrations of rhIGF-I in the circulation.

INTRODUCTION

Human and rodent research supports a primary role for IGF-I in bone formation. Significant roles for both endocrine and paracrine/autocrine IGF-I have been suggested for normal osteoblastogenesis and bone formation. We have assessed, using a mouse model of distraction osteogenesis (DO), the impact of continuous administration of recombinant human (rh)IGF-I, delivered either locally to the distraction site or absorbed systemically, on bone formation in an aged mouse model.

MATERIALS AND METHODS

DO was performed in aged mice (18-month-old C57BL/6 male mice), which were distracted at 0.15 mm daily. At the time of osteotomy, miniosmotic pumps were inserted subcutaneously to (1) deliver vehicle or rhIGF-I subcutaneously for systemic delivery or (2) deliver vehicle or rhIGF-I directly to the newly forming bone through infusion tubing routed subcutaneously from the pump to the distraction site. Serum concentrations of mouse IGF-I, human IGF-I, and osteocalcin were determined at the end of the study.

RESULTS

New bone formation observed in DO gaps showed a significant increase in new bone formation in rhIGF-I-treated mice, irrespective of delivery route. However, detectable levels of human IGF-I were found only in the serum of animals receiving rhIGF-I systemically. Osteocalcin levels did not differ between controls and rhIGF-I-treated groups.

CONCLUSIONS

Locally and systemically delivered rhIGF-I both produce significant increases in new bone formed in an aged mouse model in which new bone formation is normally markedly impaired, suggesting that rhIGF-I may improve senile osteoporosis. Because systemic administration of IGF-I can result in untoward side effects, including an increased risk for cancer, the findings that locally delivered IGF-I improves bone regeneration without increasing circulating IGF-I levels suggests that this delivery route may be preferable in an at-risk, aged population.

A novel mouse model for the study of the inhibitory effects of chronic ethanol exposure on direct bone formation

Excessive alcohol consumption has been reported to interfere with human bone homeostasis and repair in multiple ways. Previous studies have demonstrated that chronic ethanol exposure in the rat via an intragastric dietary delivery system inhibits direct bone formation during distraction osteogenesis (DO, limb lengthening). The opportunity to extend the rat ethanol studies to mice is now possible due to the development of mouse models of DO. This study employed a novel combination of liquid ethanol diet delivery and a murine DO model to test the hypothesis that chronic ethanol exposure would result in deficits in direct bone formation during DO in contrast to the pair-fed controls. Twenty-eight 12-month-old C57BL/6 male mice were acclimated to the Lieber-DeCarli liquid control diet #710027 (Dyets Inc.) over a 1-week period. The mice were separated into two diet groups (n=14/group): pair-fed control and ethanol (diet #710260). After being on diet for 82 days, all mice underwent placement of an external fixator and osteotomy on the left tibia. Following a 6-day latency period, distraction began at a rate of 0.075 mm twice a day (b.i.d.) for 14 days. The weight changes were equivalent for both groups. The hypothesis that chronic ethanol exposure would inhibit direct bone formation and produce skeletal toxicity was supported by radiographic (P=.011) and histologic (P=.002) analyses of the % new bone formation in the DO gaps, by peripheral quantitative computed tomography analysis of the total volumetric bone mineral density of the contralateral proximal tibias (P<.001) and contralateral femoral necks (P=.012), by three-point bending on the contralateral tibias (P<.001 energy to break), by pin site bone formation measures (P<.001), and by ethanol-associated increased adipocyte area (adjacent to the gap) percentages (P<.002). We conclude that this model can be used to study the mechanisms underlying inhibition of bone formation by chronic ethanol exposure and to test preclinical interventions.

Bone turnover across the menopause transition: correlations with inhibins and follicle-stimulating hormone

CONTEXT

Longitudinal clinical studies demonstrate that increases in bone turnover that occur in perimenopausal women correlate better with elevated serum FSH than with changes in serum estradiol (E2). This perimenopausal rise in FSH is due to a selective decrease in ovarian inhibin B (InhB). Our previous demonstration that inhibins suppress both osteoblast and osteoclast development suggests that changes in serum inhibins may regulate osteoblast and osteoclast differentiation and thereby bone turnover, independent of changes in sex steroids.

OBJECTIVE

The objective of this study was to determine whether decreased serum inhibin A (InhA) and InhB levels correlate with increases in markers of bone turnover in women across the menopause transition and to evaluate serum inhibins as better predictors of bone turnover markers across the menopause transition than FSH or bioavailable E2.

DESIGN

We studied a cross-sectional age-stratified population sample of 188 pre- and postmenopausal women not using oral contraceptives or hormone replacement therapy (age, 21-85 yr).

RESULTS

Serum InhA and InhB levels significantly correlated inversely with markers of bone formation and bone resorption in pre- and perimenopausal women and with markers of bone formation in postmenopausal women (InhA only). FSH was not significantly correlated with bone turnover in either pre- or postmenopausal women; however, FSH was significantly correlated with bone resorption (C-terminal collagen I cross-link) in perimenopausal women (age, 45-54 yr). Using multivariate analyses, serum InhA better predicted bone formation and resorption markers in premenopausal women than either FSH or bioavailable E2.

CONCLUSIONS

Decreases in inhibin levels across the menopause transition are associated with increasing bone turnover, regardless of changes in sex steroids or FSH.

Bone formation is impaired in a model of type 1 diabetes

The effects of type 1 diabetes on de novo bone formation during tibial distraction osteogenesis (DO) and on intact trabecular and cortical bone were studied using nonobese diabetic (NOD) mice and comparably aged nondiabetic NOD mice. Diabetic mice received treatment with insulin, vehicle, or no treatment during a 14-day DO procedure. Distracted tibiae were analyzed radiographically, histologically, and by microcomputed tomography (microCT). Contralateral tibiae were analyzed using microCT. Serum levels of insulin, osteocalcin, and cross-linked C-telopeptide of type I collagen were measured. Total new bone in the DO gap was reduced histologically (P < or = 0.001) and radiographically (P < or = 0.05) in diabetic mice compared with nondiabetic mice but preserved by insulin treatment. Serum osteocalcin concentrations were also reduced in diabetic mice (P < or = 0.001) and normalized with insulin treatment. Evaluation of the contralateral tibiae by microCT and mechanical testing demonstrated reductions in trabecular bone volume and thickness, cortical thickness, cortical strength, and an increase in endosteal perimeter in diabetic animals, which were prevented by insulin treatment. These studies demonstrate that bone formation during DO is impaired in a model of type 1 diabetes and preserved by systemic insulin administration.

Ethanol-Induced Inhibition of Bone Formation in a Rat Model of Distraction Osteogenesis: A Role for the Tumor Necrosis Factor Signaling Axis

BACKGROUND

Chronic ethanol exposure inhibits the rapid bone formation demonstrated during limb lengthening by distraction osteogenesis (DO). This inhibition is attenuated by simultaneous administration of antagonists to the cytokines interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. The individual effects on inhibition of osteogenesis by these cytokines were tested. We hypothesized that administration of individual antagonists to these cytokines [IL-1 receptor antagonist (IL-1ra) or polyethylene glycol-conjugated soluble TNF receptor type 1 (sTNFR1)] would enhance DO and that the individual administration of each cytokine [recombinant rat (rr) IL-1 or recombinant rat (rr) TNF] would inhibit DO.

METHODS

Rats were either infused with a liquid diet with or without ethanol (antagonist studies) or given rat chow (recombinant studies) and underwent tibial fractures stabilized with external fixators for DO. The bioactive substances were administered by systemic (antagonist studies) or local (recombinant) diffusion.

RESULTS

A comparison of histologic sections from these distracted tibias demonstrated a protective effect on bone formation by sTNFR1 (p<0.05), unexpectedly, an IL-1ra-related decrease in bone formation (p<0.02), significant decreases in bone formation with rrTNF compared with the vehicle controls (p<0.02), and no significant changes in bone formation with rrIL-1. The cellular responses (fibroblastic and inflammatory cells) were unique for each recombinant cytokine administered.

CONCLUSIONS

These results suggest that the osteoinhibitory effects of chronic ethanol exposure are mediated in part by the TNF signaling axis.

Regulation of bone mass by mechanical loading: microarchitecture and genetics

For decades, the processes that couple bone architecture and mass to function have been investigated and characterized. It is well known, and now well accepted, that increases in exercise and loading of bone are associated with increased bone mass, and that disuse induces osteopenia. However, the mechanisms by which disuse leads to bone loss remain poorly understood, even in the 21st century. Clearly, the skeleton is able to perceive and respond to some general input(s) generated, or lost, as a consequence of mechanical unloading of bone that are distinct from habitual activity, so called functional adaptation. It is the focus of this paper to evaluate the evidence underlying roles for genetics, osteocytes, and interstitial fluid flow in mediating disuse osteopenia.

IL-1 and TNF Antagonists Prevent Inhibition of Fracture Healing by Ethanol in Rats

We tested the hypothesis that combined administration of IL-1 and TNF antagonists would protect fracture healing from inhibition by chronic ethanol exposure. Adult male rats were fed a liquid diet +/- ethanol (CON and ETOH) by intragastric infusion for three weeks prior to and three weeks after creation of an externally fixated tibial fracture. Beginning the day of fracture, one-half of each dietary group received 2.0 mg/kg/day IL-1ra and 2.0 mg/kg/2-days sTNFR1 (CON + ANTAG and ETOH + ANTAG), while all other animals received vehicle alone (CON + VEH and ETOH + VEH). Scoring of ex vivo radiographs and analysis by pQCT revealed a significantly lower incidence of bridging and reduced total mineral content in the ETOH + VEH group compared to all other groups. These results support, for the first time, the hypothesis that IL-1 and TNF antagonists are capable of protecting fracture healing from the inhibition associated with chronic ethanol consumption.

Chronic ethanol exposure is associated with a local increase in TNF-alpha and decreased proliferation in the rat distraction gap

Chronic alcohol consumption is a risk factor for osteoporosis and inhibits osseous repair and regeneration. We investigated the hypothesis that chronic ethanol exposure induces the expression of TNF-alpha and/or IL-1beta and inhibits proliferation during distraction osteogenesis (DO). Following six weeks of liquid diet infusion (+/-ethanol) and 14 days of DO, the expression of TNF-alpha and IL-1beta in the distraction gap and contralateral femoral marrow of adult male rats was examined by immunohistochemistry and RT-PCR, respectively. In the bone marrow, the expression of both TNF-alpha and IL-1beta mRNA was significantly increased by ethanol (p<0.04 for both). In the DO gap, ethanol exposure increased the expression of TNF-alpha in both the fibrous interzone and primary matrix front (PMF), while IL-1beta expression was not significantly affected in either region. A negative correlation was found between the percentage of PCNA+ and TNF+ cells in the PMF (p<0.015, R(2)=0.655). Incubation of MC3T3-E1 cells with ethanol for 24 or 48 h produced a time and dose dependent two- to fourfold increase in TNF-alpha transcripts as measured by RT-PCR, demonstrating that ethanol can directly induce TNF-alpha expression in osteoblast-like cells. These results support the hypothesis that attenuation of bone formation by ethanol may be mediated, in part, by local increases in TNF-alpha during osteogenesis.

Interleukin-1 and tumor necrosis factor antagonists attenuate ethanol-induced inhibition of bone formation in a rat model of distraction osteogenesis

Chronic ethanol exposure inhibits rapid bone formation during distraction osteogenesis (DO; fracture and limb lengthening) and decreases volumetric bone mineral density (BMD) in a model of intragastric dietary infusion [total enteral nutrition (TEN)] in the rat. The hypothesis tested herein was that overexpression of interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha mediates these deleterious effects of ethanol on the rat skeleton. Two studies (study 1, female rats; study 2, male rats) were performed to test the potential protective effects of the IL-1 and TNF antagonists: IL-1 receptor antagonist (IL-1ra) and 30-kDa polyethylene glycol-conjugated soluble TNF receptor type 1 (sTNFR1). All rats were infused with a liquid diet +/- ethanol (EtOH) and underwent tibial fractures and DO. During distraction, the animals received a combination of IL-1ra (1.8-2.0 mg/kg/day) and sTNFR1 (2.0 mg/kg/2 days) or vehicle. A comparison of distracted tibial histological sections demonstrated 1) significant antagonist-related increases in bone column formation over the EtOH controls (studies 1 and 2), and 2) restoration of new bone equivalent to that of the TEN controls (study 2). In contrast, examination of intact proximal tibial metaphyses by peripheral quantitative computerized tomography revealed decreases in volumetric BMD of both EtOH control and EtOH antagonist groups (study 2). These results demonstrate that short-term systemic administration of IL-1 and TNF antagonists together protect rapid bone formation during DO from the deleterious effects of chronic ethanol but are ineffective in regard to intact bone homeostasis.

Skeletal toxicity associated with chronic ethanol exposure in a rat model using total enteral nutrition

Chronic alcohol abuse decreases bone mass, inhibits osteoblast differentiation and function, increases fracture incidence, and delays fracture healing. Four studies were designed to use intragastric ethanol delivery as part of a total enteral nutrition (TEN) system to determine the negative systemic effects of chronic ethanol on 1) the rat skeleton and 2) local rapid bone formation during limb lengthening (distraction osteogenesis, DO). In study 1, three-point bending tests demonstrated that after 75 days of ethanol exposure, the tibiae had significantly lower load to failure versus control diet (p = 0.0006) or ad libitum chow-fed rats (p = 0.0029). Study 2 examined alcohol's effects on the density and cross-sectional area of the proximal tibial metaphysis using peripheral quantitative computed tomography and found that after 25 days of ethanol exposure the trabecular volumetric bone mineral density (p = 0.011) and cortical cross-sectional area (p = 0.011) were lower compared with controls. In study 3, a comparison of distracted tibial radiographs and histological sections demonstrated ethanol-related decreases in both gap mineralization (p = 0.03) and bone column formation (p = 0.01). Histological comparisons in study 4 reproduced the ethanol-related deficits in new bone formation during DO (p = 0.001). These results indicate that the TEN system is a viable model to study ethanol's effects on the skeleton and that chronic ethanol delivery via TEN decreases trabecular bone density, cortical area, and mature bone strength. Also, the DO studies demonstrate, for the first time, that chronic ethanol inhibits rapid bone formation during limb lengthening.

Immunohistochemical study of osteopontin expression during distraction osteogenesis in the rat

Distraction osteogenesis (DO) is a limb-lengthening procedure that combines mechanical tension stress with fracture healing to provide a unique opportunity for detailed histological examination of bone formation. Osteopontin (OPN) is a multifunctional matricellular protein believed to play a key role in wound healing and cellular response to mechanical stress. We studied the expression of OPN during DO using standard immunohistochemical (IHC) staining techniques. In addition, we compared the expression of OPN to proliferation (PCNA-positive cells) in the DO gap. After 14 days of distraction in the rat, these stains revealed variations in OPN expression and its relationship to proliferation according to the cell type, tissue type, and mode of ossification examined. Fibroblast-like cells within the central fibrous area exhibited intermittent low levels of OPN, but no relationship was observed between OPN and proliferation. In areas of transchondral ossification, OPN expression was very high in the morphologically intermediate oval cells. During intramembranous ossification, osteoblasts appeared to exhibit a bimodal expression of OPN. Specifically, proliferating pre-osteoblasts expressed osteopontin, but OPN was not detected in the post-proliferative pre-osteoblasts/osteoblasts that border the new bone columns. Finally, intracellular OPN was detected in virtually all of the mature osteoblasts/osteocytes within the new bone columns, while detection of OPN in the matrix of the developing bone columns may increase with the maturity of the new bone. These results imply that the expression of OPN during DO may be more similar to that seen during embryogenesis than would be expected from other studies. Furthermore, the biphasic expression of OPN during intramembranous ossification may exemplify the protein's multi-functional role. Early expression may facilitate pre-osteoblastic proliferation and migration, while the latter downregulation may be necessary for hydroxyapatite crystal formation.