bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sexual Dimorphism in Vertebral Fragility Is More the Result of Gender Differences in Age-Related Bone Gain Than Bone Loss
Authors: Duan Yunbo , Turner Charles H. , Kim Bom-Taeck , Seeman Ego 
Published: April 2006

Abstract
Spine fractures usually occur less commonly in men than in women. To identify the structural basis for this gender difference in vertebral fragility, we studied 1013 healthy subjects (327 men and 686 women) and 76 patients with spine fractures (26 men and 50 women). Bone mineral content (BMC), cross-sectional area (CSA), and volumetric bone mineral density (vBMD) of the third lumbar vertebral body (L3) were measured by posteroanterior (PA) and lateral scanning using dual-energy X-ray absorptiometry (DXA). In this cross-sectional study, the diminution in peak vertebral body BMC from young adulthood to old age was less in men than in women (6% vs. 27%). This diminution was the net result of two opposing changes occurring concurrently throughout adult life: the removal of bone adjacent to marrow on the inner (endosteal) surface by bone resorption and the deposition of bone on the outer (periosteal) surface by bone formation. For L3, we estimated that men resorbed 3.7 g and deposited 3.1 g, producing a net loss of 0.6 g from young adulthood to old age and women resorbed 3.1 g and deposited only 1.2 g, producing a net loss of 1.9 g. Thus, based on our indirect estimates of periosteal gain and endosteal loss across life, the observed net diminution in BMC during aging was less in men than women because absolute periosteal bone formation was greater in men than women (3.1 g vs. 1.2 g) not because absolute bone resorption was less in men. On the contrary, the absolute amount of bone resorbed was greater in men than women (3.7 g vs. 3.1 g). Periosteal bone formation also increased vertebral body CSA 3-fold more in men than in women, distributing loads onto a larger CSA, so that the load imposed per unit CSA decreased twice as much in men than in women (13% vs. 5%). In men and women with spine fractures, CSA and vBMD were reduced relative to age-matched controls. However, vBMD was no different to the adjusted vBMD in age-matched controls derived assuming controls had no periosteal bone formation during aging. Thus, large amounts of bone are resorbed in men as well as in women, accounting for the age-related increase in spine fractures in both genders. Periosteal bone formation increases CSA and offsets bone loss in both genders but more greatly in men, accounting for the lower incidence of spine fractures in men than in women. We speculate that reduced periosteal bone formation, during growth or aging, may be in part responsible for both reduced vertebral size and reduced vBMD in men and women with spine fractures. Sexual dimorphism in vertebral fragility is more the result of gender differences in age-related bone gain than age-related bone loss.
The Biomechanical Basis of Vertebral Body Fragility in Men and Women
Authors: Duan Yunbo , Seeman Ego , Turner Charles H. 
Published: April 2006

Abstract
The aim of this study was to quantify the biomechanical basis for vertebral fracture risk in elderly men and women. A bone is likely to fracture when the loads imposed are similar to or greater than its strength. To quantify this risk, we developed a fracture risk index (FRI) based on the ratio of the vertebral body compressive load and strength. Loads were determined by upper body weight, height, and the muscle moment arm, and strength was estimated from cross-sectional area (CSA) and volumetric bone mineral density (vBMD). With loads less than the strength of the bone, the FRI remains &lt;1. For any given load, once bone strength diminishes due to a falling vBMD, the FRI will increase. Should FRI approach or exceed unity, structural failure of the vertebra is likely. We measured vertebral body CSA vBMD of the middle zone of third lumbar vertebra by lateral and posteroanterior (PA) scanning using dual-energy X-ray absorptiometry (DXA) and calculated vertebral compressive stress (load per unit area) in 327 healthy men and 686 healthy women and 26 men and 55 postmenopausal women with vertebral fractures. Activities that require forward bending of the upper body caused ∼10-fold more compressive stress on the vertebra compared with standing upright. Men and women had similar peak vBMD in young adulthood. Because men have greater stature than women, the loads imposed on the vertebral body are higher (3754 ± 65 N vs. 3051 ± 31 N; p &lt; 0.001). However, because CSA also was higher in men than women, peak load per unit CSA (stress) did not differ by gender (317.4 ± 4.7 N/cm2 vs. 321.9 ± 3.3 N/cm2, NS). The FRI was similar in young men and women and well below unity (0.42 ± 0.02 vs. 0.43 ± 0.01; NS). Gender differences emerged during aging; CSA increased in both men and women but more so in men, so load per unit area (stress) diminished but more so in men than in women. vBMD decreased in both genders but less so in men. These changes were captured in the FRI, which increased by only 21% in men and by 102% in women so that only 9% of elderly men but 26% of elderly women had an FRI ≥ 1. Men and women with vertebral fractures had an FRI that was greater than or equal to unity (1.03 ± 0.13 vs. 1.35 ± 0.13; p &lt; 0.05) and was 2.04 SD and 2.26 SD higher than age-matched men and women, respectively. In summary and conclusion, young men and women have a similar vBMD, vertebral stress, and FRI. During aging, CSA increases more, and vBMD decreases less in men than in women. Thus, fewer men than women are at risk for fracture because fewer men than women have these structural determinants of bone strength below a level at which the loads exceed the bone's ability to tolerate them. Men and women with vertebral fractures have FRIs that are equal to or exceed unity. The results show that a fracture threshold for vertebrae can be defined using established biomechanical principles; whether this approach has greater sensitivity and specificity than the current BMD T score of −2.5 SD is unknown.
Mechanical Loading of Diaphyseal Bone In Vivo: The Strain Threshold for an Osteogenic Response Varies with Location
Authors: Hsieh Yeou-Fang , Robling Alexander G. , Ambrosius Walter T. , Burr David B. , Turner Charles H. 
Published: April 2006

Abstract
Bone tissue responds to elevated mechanical loading with increased bone formation, which is triggered either directly or indirectly by the mechanical strain engendered in the bone tissue. Previous studies have shown that mechanical strain magnitude must surpass a threshold before bone formation is initiated. The objective of this study was to estimate the strain thresholds at three different locations along the ulna of adult rats. We hypothesized that the strain threshold would be greater in regions of the ulna habitually subjected to larger mechanical strains. New bone formation was measured on the periosteal and endocortical surfaces of the ulnar diaphysis in adult female rats exposed to controlled dynamic loading. Axial, compressive loading was applied daily at five different magnitudes for a period of 2 weeks. Bone formation rate (BFR) was measured, using double-label histomorphometry at the ulnar middiaphysis and at locations 3 mm proximal and 3 mm distal to the middiaphysis. Loading induced lamellar bone formation on the periosteal surface that was greater at the distal ulnar location and lower at the proximal location when compared with the middiaphysis. Likewise, peak strains on the periosteal surface were greatest distally and less proximally. There was a significant dose-response relationship between peak strain magnitude and periosteal new bone formation when the mechanically induced strain surpassed a threshold. The strain threshold varied from 1343 microstrain (μstrain) proximally to 2284 μstrain at the midshaft to 3074 μstrain distally. Unlike the periosteal response to mechanical loading, there was not a clear dose-response relationship between applied load and bone formation on the endocortical surface. Endocortical strains were estimated to be &lt;20% of periosteal strains and may not have been sufficient to initiate a bone formation response. Our results show that the osteogenic response on the periosteal surface of the ulna depends on peak strain level once a strain threshold is surpassed. The threshold strain is largest distally, where locomotor bone strains are typically higher and smallest proximally where locomotor bone strains are lower.
The Skeletal Structure of Insulin-Like Growth Factor I-Deficient Mice
Authors: Bikle Daniel , Majumdar Sharmila , Laib Andres , Powell-Braxton Lyn , Rosen Clifford , Beamer Wesley , Nauman Eric , Leary Colin , Halloran Bernard 
Published: April 2006

Abstract
The importance of insulin-like growth factor I (IGF-I) for growth is well established. However, the lack of IGF-I on the skeleton has not been examined thoroughly. Therefore, we analyzed the structural properties of bone from mice rendered IGF-I deficient by homologous recombination (knockout [k/o]) using histomorphometry, peripheral quantitative computerized tomography (pQCT), and microcomputerized tomography (μCT). The k/o mice were 24% the size of their wild-type littermates at the time of study (4 months). The k/o tibias were 28% and L1 vertebrae were 26% the size of wild-type bones. Bone formation rates (BFR) of k/o tibias were 27% that of the wild-type littermates. The k/o bones responded normally to growth hormone (GH; 1.7-fold increase) and supranormally to IGF-I (5.2-fold increase) with respect to BFR. Cortical thickness of the proximal tibia was reduced 17% in the k/o mouse. However, trabecular bone volume (bone volume/total volume [BV/TV]) was increased 23% (male mice) and 88% (female mice) in the k/o mice compared with wild-type controls as a result of increased connectivity, increased number, and decreased spacing of the trabeculae. These changes were either less or not found in L1. Thus, lack of IGF-I leads to the development of a bone structure, which, although smaller, appears more compact.
Activation of Transforming Growth Factor β in Chondrocytes Undergoing Endochondral Ossification
Authors: D'Angelo Marina , Sarment David P. , Billings Paul C. , Pacifici Maurizio 
Published: April 2006

Abstract
Transforming growth factor β (TGF-β) has well-documented roles in chondrocyte maturation and endochondral ossification, but the mechanisms of TGF-β activation during these processes remain unclear. In this study, we analyzed TGF-β activation in chick embryo resting, proliferating, and hypertrophic chondrocytes in culture. We found that both levels and activation of TGF-β increased substantially with maturation. The majority of TGF-β produced by resting cells over culture time remained latent, but a larger portion produced by proliferating and hypertrophic cells was activated with increasing maturation. Zymography of gelatin gels revealed that matrix metalloprotease 2 (MMP-2) and MMP-9 were expressed by each population and that MMP-13 characterized hypertrophic chondrocytes and to a lesser extent proliferating chondrocytes in late cultures. Treatment with pharmacologic agents revealed that both MMPs and serine proteases are involved in activation. However, because inhibition of MMPs almost completely prevented TGF-β activation, MMPs appear crucial for activation. During culture, inclusion of the tetracycline-derived, collagenase/gelatinase inhibitor chemically modified nonantimicrobial tetracycline (CMT-8) at concentrations specific for MMP-13 inhibition resulted in complete inhibition of TGF-β activation by proliferating and hypertrophic chondrocytes. These results show that TGF-β production, release, and activation are regulated developmentally in chondrocytes. Our findings point to a strict mode of regulation of this potent factor to elicit diverse and highly specific effects during chondrocyte maturation and ossification.
Localization of Estrogen Receptor β Protein Expression in Adult Human Bone
Authors: Braidman Isobel P. , Hainey Linda , Batra Gaurav , Selby Peter L. , Saunders Philippa T.K. , Hoyland Judith A. 
Published: April 2006

Abstract
Evidence suggests that the newly described estrogen receptor β (ER-β) may be important for estrogen (17β-estradiol) action on the skeleton, but its cellular localization in adult human bone requires clarification. We addressed this by using indirect immunoperoxidase with a novel affinity purified polyclonal antibody to human ER-β, raised to hinge domain (D) sequences from the human receptor. Bone was demineralized in 20% EDTA and all biopsy specimens were formalin-fixed and wax-embedded. Vigorous retrieval was essential for ER-β detection. In sections (5 μm) of benign prostate hyperplasia, used as positive control, clear nuclear immunoreactivity was seen in glandular epithelial cells, with a 1:500 dilution of ER-β40. For bone sections, optimal antibody dilutions were 1:100–1:250. We found that in normal bone (from graft operations), in fracture callus from both men and women (&gt;25 years old), pagetic bone, osteophytes, and secondary hyperparathyroid bone, all from older patients, ER-β was expressed clearly in osteoclast nuclei, with little cytoplasmic immunoreactivity. Nuclear immunoreactivity was still prominent in osteoclasts, with antibody diluted 1:500, although it faded in other cells. Osteoblasts, in areas of active bone formation or bone remodeling, also expressed ER-β, as did some osteocytes. However, hypertrophic chondrocytes were negative, unlike mesenchymal cells, adjacent to the osteogenesis. Megakaryocytes and some capillary blood vessels cells were receptor positive. All ER-β expression was blocked totally by preincubation of antibody with antigen. We conclude that ER-β is expressed in cells of osteoblast lineage and in osteoclasts. The latter appear relatively abundant in this receptor and this might provide a means for direct action of estrogen on osteoclasts.
Transcriptional Induction of Matrix Metalloproteinase-13 (Collagenase-3) by 1α,25-Dihydroxyvitamin D3 in Mouse Osteoblastic MC3T3-E1 Cells
Authors: Uchida Motoyuki , Shima Masaaki , Chikazu Daichi , Fujieda Ayako , Obara Kazumi , Suzuki Hiroyuki , Nagai Yumiko , Yamato Hideyuki , Kawaguchi Hiroshi 
Published: April 2006

Abstract
The removal of unmineralized matrix from the bone surface is essential for the initiation of osteoclastic bone resorption because osteoclasts cannot attach to the unmineralized osteoid. Matrix metalloproteinases (MMPs) are known to digest bone matrix. We recently reported that among the MMPs expressed in mouse osteoblastic cells, MMP-13 (collagenase-3) was the one most predominantly up-regulated by bone resorbing factors including 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3]. In this study, we examined the mechanism of regulation of MMP-13 expression by 1α,25(OH)2D3 in mouse osteoblastic MC3T3-E1 cells. 1α,25(OH)2D3 increased steady-state messenger RNA (mRNA) and protein levels of MMP-13. De novo protein synthesis was essential for the induction because cycloheximide (CHX) decreased the effect of 1α,25(OH)2D3 on the MMP-13 mRNA level. 1α,25(OH)2D3 did not alter the decay of MMP-13 mRNA in transcriptionally arrested MC3T3-E1 cells; however, it increased the MMP-13 heterogeneous nuclear RNA (hnRNA) level and MMP-13 transcriptional rate. The binding activity of nuclear extracts to the AP-1 binding site, but not to the Cbfa1 binding site, in the MMP-13 promoter region was up-regulated by 1α,25(OH)2D3, suggesting the mediation of AP-1 in this transcriptional induction. To determine the contribution of MMPs to bone resorption by 1α,25(OH)2D3, the inhibitory effect of BB94, an MMP inhibitor, on resorbed pit formation by mouse crude osteoclastic cells was examined on either an uncoated or collagen-coated dentine slice. BB94 did not prevent resorbed pit formation on uncoated dentine whereas it did on collagen-coated dentine. We therefore propose that the transcriptional induction of MMP-13 in osteoblastic cells may contribute to the degradation of unmineralized matrix on the bone surface as an early step of bone resorption by 1α,25(OH)2D3.
Bioactive Glass Stimulates In Vitro Osteoblast Differentiation and Creates a Favorable Template for Bone Tissue Formation
Authors: Loty C. , Sautier J. M. , Tan M. T. , Oboeuf M. , Jallot E. , Boulekbache H. , Greenspan D. , Forest N. 
Published: April 2006

Abstract
In this study, we have investigated the behavior of fetal rat osteoblasts cultured on bioactive glasses with 55 wt% silica content (55S) and on a bioinert glass (60S) used either in the form of granules or in the form of disks. In the presence of Bioglass granules (55 wt% silica content), phase contrast microscopy permitted step-by-step visualization of the formation of bone nodules in contact with the particles. Ultrastructural observations of undecalcified sections revealed the presence of an electron-dense layer composed of needle-shaped crystals at the periphery of the material that seemed to act as a nucleating surface for biological crystals. Furthermore, energy dispersive X-ray (EDX) analysis and electron diffraction patterns showed that this interface contains calcium (Ca) and phosphorus (P) and was highly crystalline. When rat bone cells were cultured on 55S disks, scanning electron microscopic (SEM) observations revealed that cells attached, spread to all substrata, and formed multilayered nodular structures by day 10 in culture. Furthermore, cytoenzymatic localization of alkaline phosphatase (ALP) and immunolabeling with bone sialoprotein antibody revealed a positive staining for the bone nodules formed in cultures on 55S. In addition, the specific activity of ALP determined biochemically was significantly higher in 55S cultures than in the controls. SEM observations of the material surfaces after scraping off the cell layers showed that mineralized bone nodules remained attached on 55S surfaces but not on 60S. X-ray microanalysis indicated the presence of Ca and P in this bone tissue. The 55S/bone interfaces also were analyzed on transverse sections. The interfacial analysis showed a firm bone bonding to the 55S surface through an intervening apatite layer, confirmed by the X-ray mappings. All these results indicate the importance of the surface composition in supporting differentiation of osteogenic cells and the subsequent apposition of bone matrix allowing a strong bond of the bioactive materials to bone.
Parathyroid Hormone Enhances Fluid Shear-Induced [Ca2+]i Signaling in Osteoblastic Cells Through Activation of Mechanosensitive and Voltage-Sensitive Ca2+ Channels
Authors: Ryder Kimberly D. , Duncan Randall L. 
Published: April 2006

Abstract
Osteoblasts respond to both fluid shear and parathyroid hormone (PTH) with a rapid increase in intracellular calcium concentration ([Ca2+]i). Because both stimuli modulate the kinetics of the mechanosensitive cation channel (MSCC), we postulated PTH would enhance the [Ca2+]i response to fluid shear by increasing the sensitivity of MSCCs. After a 3-minute preflow at 1 dyne/cm2, MC3T3-E1 cells were subjected to various levels of shear and changes in [Ca2+]i were assessed using Fura-2. Pretreatment with 50 nM bovine PTH(1–34) [bPTH(1–34)] significantly enhanced the shear magnitude-dependent increase in [Ca2+]i. Gadolinium (Gd3+), an MSCC blocker, significantly inhibited the mean peak [Ca2+]i response to shear and shear + bPTH(1–34). Nifedipine (Nif), an L-type voltage-sensitive Ca2+ channel (VSCC) blocker, also significantly reduced the [Ca2+]i response to shear + bPTH(1–34), but not to shear alone, suggesting VSCC activation plays an interactive role in the action of these stimuli together. Activation of either the protein kinase C (PKC) or protein kinase A (PKA) pathways with specific agonists indicated that PKC activation did not alter the Ca2+ response to shear, whereas PKA activation significantly increased the [Ca2+]i response to lower magnitudes of shear. bPTH(1–34), which activates both pathways, induced the greatest [Ca2+]i response at each level of shear, suggesting an interaction of these pathways in this response. These data indicate that PTH significantly enhances the [Ca2+]i response to shear primarily via PKA modulation of the MSCC and VSCC.
The Transition of Cadherin Expression in Osteoblast Differentiation from Mesenchymal Cells: Consistent Expression of Cadherin-11 in Osteoblast Lineage
Authors: Kawaguchi Jitsutaro , Kii Isao , Sugiyama Yutaro , Takeshita Sunao , Kudo Akira 
Published: April 2006

Abstract
Osteoblasts are derived originally from pluripotent mesenchymal stem cells on migration into the bone matrix. To elucidate the contribution of classical cadherins in this differentiation pathway, we developed a new protocol for their analysis and studied their specific expressions in various cell lines of the mesenchymal lineage, including osteoblasts. N-cadherin was expressed constitutively in all cell lines examined except an osteocyte-like cell line whereas cadherin-11 was expressed selectively in preosteoblast and preadipocyte cell lines. P-cadherin also was expressed in primary cultures of calvarial cells and mature osteoblasts at a relatively low level compared with N-cadherin and cadherin-11. M-cadherin was expressed only in a premyoblast cell line. We observed the transition of cadherin expression from M-cadherin to cadherin-11 in the premyoblast cell line when osteogenic differentiation was induced by treatment with bone morphogenetic protein 2 (BMP-2), while the expression of N-cadherin remained unchanged. In contrast, when a preadipocyte cell line, which shows a similar pattern of cadherin expression to osteoblasts, was induced to undergo adipogenic differentiation, the expression of N-cadherin and cadherin-11 was decreased. These observations characterize the cadherin expression profile of mesenchymal lineage cells, especially osteoblasts, which regularly express cadherin-11. Cadherin-11 may affect cell sorting, alignment, and separation through differentiation.