bluuebunny/crossref_metadata_2025_split huggingface dataset:
Randomized Controlled Study of Effects of Sudden Impact Loading on Rat Femur
Authors: Järvinen Teppo L. N. , Kannus Pekka , Sievänen Harri , Jolma Pasi , Heinonen Ari , Järvinen Markku 
Published: April 2006

Abstract
Physical loading creating high peak strains on the skeleton at high strain rates is suggested to be the most effective type of activity in terms of bone mineral acquisition. This study assessed the effects of sudden impact loading on mineral and mechanical bone properties in 13-week-old Sprague-Dawley rats. The rats were randomly assigned as sedentary controls (SED, n = 10), control animals receiving low-intensity exercise (EX, n = 15), and experimental animals receiving low-intensity exercise combined with sudden impact-loading (EX + IMP, n = 15). In the EX group, the rats walked in a walking mill at a speed of 10 cm/s for 20 minutes/day, 5 days/week for 9 weeks. In the EX + IMP group, the program was identical to the EX group except for the additional sudden impacts administered to their skeleton during the walking exercise. At the start, there were 50 impacts per session, after which their number was gradually increased to 200 impacts per session by week 6 and then kept constant until the end of the experiment, week 9. These horizontally and vertically directed body impacts were produced by a custom-made walking mill equipped with computer-controlled high-pressure air cylinders. After sacrifice, both femora of each rat were removed and their dimensions, bone mineral content (BMC) by dual-energy X-ray absorptiometry, and mechanical properties by femoral shaft three-point bending and femoral neck compression were determined. The cortical wall thickness increased significantly in the EX and EX + IMP groups as compared with SEDs (+7.6%, p = 0.049 and +10%, p = 0.020, respectively). The EX + IMP group showed +9.0% (p = 0.046) higher cross-sectional moment of inertia values than the EX group. No significant intergroup differences were seen in the BMC values, while the breaking load of the femoral shaft (EX + IMP vs. SED +8.8%, p = 0.047) and femoral neck (EX + IMP vs. SED +14.1%, p = 0.013) was significantly enhanced by the impact loading. In conclusion, this study indicates that mechanical loading can substantially improve the mechanical characteristics of a rat femur without simultaneous gain in its mineral mass. If this is true in humans too, our finding gives an interesting perspective to the numerous longitudinal exercise studies (of women) in which the exercise-induced gains in bone mass and density have remained mild to moderate only.
Effect of Recombinant Human Bone Morphogenetic Protein-2 on Fracture Healing in a Goat Tibial Fracture Model
Authors: Welch Robert D. , Jones Alan L. , Bucholz Robert W. , Reinert Charles M. , Tjia Jane S. , Pierce William A. , Wozney John M. , Li X. Jian 
Published: April 2006

Abstract
Bone morphogenetic proteins (BMPs) are considered to have important regulatory roles in skeletal embryogenesis and bone healing. Recombinant human BMPs (rhBMPs) have been shown to heal critical size defects and promote spinal fusion. We studied the effects of rhBMP-2 in an absorbable collagen sponge (ACS) on bone healing in a large animal tibial fracture model. Bilateral closed tibial fractures were created in 16 skeletally mature goats and reduced and stabilized using external fixation. In each animal, one tibia received the study device (0.86 mg of rhBMP-2/ACS or buffer/ACS), and the contralateral fracture served as control. The device was implanted as a folded onlay or wrapped circumferentially around the fracture. Six weeks following fracture, the animals were sacrificed and the tibiae harvested for torsional testing and histomorphologic evaluation. Radiographs indicated increased callus at 3 weeks in the rhBMP-2/ACS treated tibiae. At 6 weeks, the rhBMP-2/ACS wrapped fractures had superior radiographic healing scores compared with buffer groups and controls. The rhBMP-2/ACS produced a significant increase in torsional toughness (p = 0.02), and trends of increased torsional strength and stiffness (p = 0.09) compared with fracture controls. The device placed in a wrapped fashion around the fracture produced significantly tougher callus (p = 0.02) compared with the onlay application. Total callus new bone volume was significantly increased (p = 0.02) in the rhBMP-2/ACS fractures compared with buffer groups and controls regardless of the method of device application. The rhBMP-2/ACS did not alter the timing of onset of periosteal/endosteal callus formation compared with controls. Neither the mineral apposition rates nor bone formation rates were affected by rhBMP-2/ACS treatment. The increased callus volume associated with rhBMP-2 treatment produced only moderate increases in strength and stiffness.
Dual Signaling and Ligand Selectivity of the Human PTH/PTHrP Receptor
Authors: Takasu Hisashi , Guo Jun , Bringhurst F. Richard 
Published: April 2006

Abstract
Parathyroid hormone (PTH) activates PTH/PTH-related peptide-related receptors (PTHRs) to stimulate both adenylyl cyclase (AC) and phospholipase C (PLC). How these parallel signals mediate specific cellular and tissue responses to PTH, such as the complex anabolic versus catabolic actions of PTH on bone, remains unsettled. Previous studies of PTHR signaling and function employed mainly rodent or other cell lines that express endogenous PTHRs and, possibly, alternate species of PTH receptors. To preclude confounding effects of such receptors, we stably expressed recombinant human PTHRs (hPTHRs) at different levels of surface density in LLC-PK1 porcine renal epithelial cells that lack endogenous PTH responsiveness. hPTH(1–34) induced concentration-dependent activation of both AC and PLC via transfected hPTHRs. Maximal intensity of each signal increased with receptor density, but more hPTHRs were required for PLC than for AC activation. Coupling to AC was saturated at receptor densities too low to detect sustained PLC activation. hPTH(3–34), found by others to be a PLC/protein kinase C (PKC)-selective peptide in rat cells, did not activate PLC via human (or rat) PTHRs under conditions (1 μM peptide, 106 hPTHRs/cell) where hPTH(1–34) stimulated PLC severalfold. Other cellular responses that require PKC activation in these cells, such as sodium-dependent phosphate transport and cAMP-independent secretion of plasminogen activator, were induced by PTH(1–34) but not by hPTH(3–34) or hPTH(7–34). We conclude that amino-truncated PTH analogs reported to activate PKC cannot directly activate phosphatidylinositol-specific PLC via the human or rat PTHR and therefore that PTH receptors may access alternate, PLC-independent pathways of PKC activation in some target cells. The relative intensity of AC and PLC signaling via the hPTHR may be strongly regulated by changes in its surface expression.
Site-Specific Effects of Strength Training on Bone Structure and Geometry of Ultradistal Radius in Postmenopausal Women
Authors: Adami Silvano , Gatti Davide , Braga Vania , Bianchini Donatella , Rossini Maurizio 
Published: April 2006

Abstract
Knowledge of the effects of exercise on bone mass in postmenopausal women is limited and controversial. Animal studies have shown that the response of bone to bending strain is an alteration of bone geometry. We studied 250 postmenopausal women, aged 52–72 years, willing to participate in a 6-month exercise program. The first 125 started the program immediately and the remaining 125 served as controls. The training program included exercises designed to maximize the stress on the wrist. One hundred and eighteen of the active group and 116 of the control group completed the study and were reassessed 6 months later. Bone mineral density (BMD) of the femoral neck, lumbar spine, ultradistal and proximal radius was measured by dual-energy X-ray absorptiometry (DXA) both before and at the end of the exercise program. The forearm was also evaluated by peripheral quantitative computed tomography, which measures the area, bone mineral content (BMC), and volumetric density for both the cortical and the trabecular component. The results showed that the DXA measurements at the femoral neck, lumbar spine, ultradistal and proximal radius were similar between the two groups. No significant difference was detected after the exercise program at the proximal radius. At the ultradistal radius, the cross-sectional area of cortical bone rose by 2.8 ± 15.0% (SD, p &lt; 0.05), apparently for both periosteal apposition and corticalization of the trabecular tissue. The volumetric density of cortical bone rose by 2.2 ± 15.8% (p &lt; 0.1), and that of trabecular bone decreased by 2.6 ± 10.7% (p &lt; 0.01). The combined changes in both bone volume and density in the exercise group were associated with marked increase in cortical BMC (3.1 ± 10.7%, p &lt; 0.01) and decrease in trabecular BMC (−3.4 ± 14.2%, p &lt; 0.05), which were statistically different from those observed in the control group (p &lt; 0.05). In conclusion, these results confirm that site-specific moderate physical exercises have very little effect on bone mass. However, it appears that some exercises may reshape the bone segment under stress by increasing both the cross-sectional area and the density of the cortical component. These structural changes are theoretically associated with increases in the bending strength.
Skeletal Unloading Causes Resistance of Osteoprogenitor Cells to Parathyroid Hormone and to Insulin-like Growth Factor-I
Authors: Kostenuik Paul J. , Harris Jonathan , Halloran Bernard P. , Turner Russell T. , Morey-Holton Emily R. , Bikle Daniel D. 
Published: April 2006

Abstract
Skeletal unloading decreases bone formation and osteoblast number in vivo and decreases the number and proliferation of bone marrow osteoprogenitor (BMOp) cells in vitro. We tested the ability of parathyroid hormone (PTH) to stimulate BMOp cells in vivo by treating Sprague Dawley rats (n = 32) with intermittent PTH(1–34) (1 h/day at 8 μ g/100 g of body weight), or with vehicle via osmotic minipumps during 7 days of normal weight bearing or hind limb unloading. Marrow cells were flushed from the femur and cultured at the same initial density for up to 21 days. PTH treatment of normally loaded rats caused a 2.5-fold increase in the number of BMOp cells, with similar increases in alkaline phosphatase (ALP) activity and mineralization, compared with cultures from vehicle-treated rats. PTH treatment of hind limb unloaded rats failed to stimulate BMOp cell number, ALP activity, or mineralization. Hind limb unloading had no significant effect on PTH receptor mRNA or protein levels in the tibia. Direct in vitro PTH challenge of BMOp cells isolated from normally loaded bone failed to stimulate their proliferation and inhibited their differentiation, suggesting that the in vivo anabolic effect of intermittent PTH on BMOp cells was mediated indirectly by a PTH-induced factor. We hypothesize that this factor is insulin-like growth factor-I (IGF-I), which stimulated the in vitro proliferation and differentiation of BMOp cells isolated from normally loaded bone, but not from unloaded bone. These results suggest that IGF-I mediates the ability of PTH to stimulate BMOp cell proliferation in normally loaded bone, and that BMOp cells in unloaded bone are resistant to the anabolic effect of intermittent PTH therapy due to their resistance to IGF-I.
Studies of the Murine Homolog of the Multiple Endocrine Neoplasia Type 1 (MEN1) Gene, men1
Authors: Bassett J. H. D. , Rashbass P. , Harding B. , Forbes S. A. , Pannett A. A. J. , Prof. Thakker R. V. 
Published: April 2006

Abstract
The murine homolog of the multiple endocrine neoplasia type 1 (MEN1) gene (men1), which in humans is associated with tumors of the parathyroids, pancreas, and pituitary, has been characterized by isolating 27 clones from a mouse embryonic stem cell cDNA library. The insert sizes ranged from 600–2500 bp, and sequence analysis identified a 1833 bp open reading frame encoding a 611 amino acid protein. In addition, two clones contained an unspliced intron 1, and another two clones contained 20–29 bp of an upstream sequence, which suggested the presence of an alternate exon 1. This was supported by an analysis of the homologous human sequence. The mouse and human coding regions had 89% and 96% identity of the nucleotide and amino acid sequences, respectively. Investigation of clones isolated from a 129ola mouse genomic library, revealed the men1 gene to consist of 10 exons that spanned ∼6 kb. Northern blot analysis demonstrated the ubiquitous expression of 2.9 kb and 3.4 kb transcripts in mouse adult tissues and embryos from 7 days. DNA sequence analysis of the larger 3.4 kb transcript revealed it to result from a retention of intron 1. In situ hybridization confirmed an early ubiquitous expression in whole mount mouse embryos and adult tissues, but in the latter, different levels of cellular expression were observed, e.g., men1 expression was higher in testicular Sertoli cells than in germ cells. Thus, the mouse men1 gene and the basis of alternative transcripts have been defined, and these will help to facilitate studies of a mouse model.
The Integrin αvβ5 Is Expressed on Avian Osteoclast Precursors and Regulated by Retinoic Acid
Authors: Sago Karen , Teitelbaum Steven L. , Venstrom Kristy , Reichardt Louis F. , Ross F. Patrick 
Published: April 2006

Abstract
Osteoclasts arise by proliferation, differentiation, and subsequent fusion of marrow-derived precursors, all processes requiring attachment to matrix. Integrins are important mediators of cell-matrix recognition and bone is rich in proteins containing the Arg-Gly-Asp motif, recognized primarily by αv integrins. Thus, we determined if avian osteoclast precursors express integrins capable of mediating initial attachment to matrix proteins. Early, marrow-derived osteoclast precursors, when first isolated, contain no detectable αvβ3, but express an αv integrin with an 80 kDa associated β subunit. Immunoprecipitation with an antibody raised against the conserved β5 cytoplasmic tail sequence indicates the the αv associated the integrin is αvβ5. Retinoic acid is a resorptive steroid, and its exposure to early osteoclast precursors prompts a time- and dose-dependent decrease in αvβ5 expression, while simultaneously stimulating αvβ3 expression. Northern analysis reveals that retinoic acid decreases β5 steady-state mRNA, nontranscriptionally, without altering that of αv. The finding αvβ5 expression decreases under the influence of retinoic acid, an osteoclastogenic steroid, while those of αvβ3 rise, suggests that these closely related integrins play separate and complementary roles during osteoclast differentiation.
Evidence for Involvement of 17β-Estradiol in Intestinal Calcium Absorption Independent of 1,25-Dihydroxyvitamin D3 Level in the Rat
Authors: Colin E. M. , Van Den Bemd G. J. C. M. , Van Aken M. , Christakos S. , De Jonge H. R. , Deluca H. F. , Prahl J. M. , Birkenhäger J. C. , Buurman C. J. , Pols H. A. P. , van Leeuwen J. P. T. M. 
Published: April 2006

Abstract
The sex steroid 17β-estradiol (17β-E2) has a broad range of actions, including effects on calcium and bone metabolism. This study with 3-month-old Brown Norway rats was designed to investigate the role of 17β-E2 in the regulation of calcium homeostasis. Rats were divided in four groups, sham-operated, ovariectomized (OVX), and OVX supplemented with either a 0.025-mg or 0.05-mg 17β-E2 pellet implanted subcutaneously. After 4 weeks, in none of the groups was serum calcium, phosphate, or parathyroid hormone altered compared with the sham group, while only in the OVX rats was a significant reduction in urinary calcium found. Bone mineral density and osteocalcin were modified, as can be expected after OVX and 17β-E2 supplementation. OVX resulted in a nonsignificant increase in serum 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Supplementation with either one of the 17β-E2 dosages resulted in an 80% reduction of 1,25(OH)2D3 and only a 20% reduction in 25-hydroxyvitamin D3 levels. OVX, as well as supplementation with 17β-E2, did not affect serum levels of vitamin D binding protein. As a consequence, the estimated free 1,25(OH)2D3 levels were also significantly decreased in the 17β-E2-supplemented group compared with the sham and OVX groups. Next, the consequences for intestinal calcium absorption were analyzed by the in situ intestinal loop technique. Although the 1,25(OH)2D3 serum level was increased, OVX resulted in a significant decrease in intestinal calcium absorption in the duodenum. Despite the strongly reduced 1,25(OH)2D3 levels (18.1 ± 2.1 and 16.4 ± 2.2 pmol/l compared with 143.5 ± 29 pmol/l for the OVX group), the OVX-induced decrease in calcium absorption could partially be restored by supplementation with either 0.025 mg or 0.05 mg of 17β-E2. None of the treatments resulted in a significant change in calcium handling in the jejunum, although the trends were similar as those observed in the duodenum. 17β-E2 did not change the VDR levels in both the intestine and the kidney. In conclusion, the present study demonstrates that 17β-E2 is positively involved in intestinal calcium absorption, and the data strengthen the assertion that 17β-E2 exerts this effect independent of 1,25(OH)2D3. In general, 17β-E2 not only affects bone turnover but also calcium homeostasis via an effect on intestinal calcium absorption.
Human NELL-1 Expressed in Unilateral Coronal Synostosis
Authors: Dr. Ting Kang , Vastardis Heleni , Mulliken John B. , Soo Chia , Tieu Andy , Do Huy , Kwong Emily , Bertolami Charles N. , Kawamoto Henry , Kuroda Shun'ichi , Longaker Michael T. 
Published: April 2006

Abstract
Surgical correction of unilateral coronal synostosis offers a unique opportunity to examine the molecular differences between an abnormal and a normal cranial suture. We isolated and identified a cDNA fragment whose expression was up-regulated in the premature fusing and fused coronal sutures, as compared with normal coronal sutures. The nucleotide sequence of the full-length cDNA of this gene, human NELL-1, has ∼61% homology with the chicken Nel gene. Both chicken Nel and human NELL-1 are comprised of six epidermal growth factor-like repeats. The human NELL-1 messages were localized primarily in the mesenchymal cells and osteoblasts at the osteogenic front, along the parasutural bone margins, and within the condensing mesenchymal cells of newly formed bone in sites of premature sutural fusion. Human multiorgan tissue mRNA blot showed that NELL-1 was specifically expressed in fetal brain but not in fetal kidney, liver, or lung. We also showed that Nell-1 was expressed in rat calvarial osteoprogenitor cells and was largely absent in rat tibiae and fibroblast cell cultures. In conclusion, our data suggest that the NELL-1 gene is preferentially expressed in cranial intramembranous bone and neural tissue (both of neural crest cell origin) and is up-regulated during unilateral premature closure of the coronal suture. The precise role of this gene is unknown.
1,25-Dihydroxyvitamin D3–Induced Calcium Efflux from Calvaria Is Mediated by Protein Kinase C
Authors: Dranitzki-Elhalel Michal , Wald Hanna , Popovtzer Mordecai M. , Sprague Stuart M. 
Published: April 2006

Abstract
1,25-dihydroxyvitamin D3 (1,25(OH)2D3) is an important regulator of bone metabolism involved in both formation and resorption. Traditionally it was assumed that vitamin D receptors are intracellular. Recent data indicate that vitamin D may also act through a membrane receptor, specifically raising intracellular calcium and inositol 1,4,5 triphosphate. The present study was undertaken to explore further the mechanism(s) of vitamin D–induced bone resorption in cultured bone. 1,25(OH)2D3 induced a dose-dependent increase of calcium efflux from cultured bone. This increase was completely obliterated by inhibition of protein kinase C (PKC) with either staurosporine or calphostin C. In cultured rat calvariae, 1,25(OH)2D3 also induced a dose-dependent translocation of PKC from cytosol to membrane. The activation of PKC by 1,25(OH)2D3 occurred following a 30-s incubation, peaked at 1 minute, and disappeared by 5 minutes. 1,25(OH)2D3 did not increase cAMP production in similarly cultured calvaria. These results suggest that the action of 1,25(OH)2D3 on calcium flux from cultured bone is mediated, in part, via activation of PKC.
Parathyroid Hormone–Related Protein Regulates Proliferation of Condylar Hypertrophic Chondrocytes
Authors: Suda Naoto , Shibata Shunichi , Yamazaki Kiyomi , Kuroda Takayuki , Senior Paul V. , Beck Felix , Hammond Vicki E. 
Published: April 2006

Abstract
The condylar cartilage, an important growth site in the mandible, shows characteristic modes of growth and differentiation, e.g., it shows delayed appearance in development relative to the limb bud cartilage, originates from the periosteum rather than from undifferentiated mesenchymal cells, and shows rapid differentiation into hypertrophic chondrocytes as opposed to the epiphyseal growth plate cartilage, which has resting and proliferative zones. Recently, attention has been focused on the role of parathyroid hormone–related protein (PTHrP) in modulating the proliferation and differentiation of chondrocytes. To investigate further the characteristic modes of growth and differentiation of this cartilage, we used mice with a disrupted PTHrP allele. Immunolocalization of type X collagen, the extracellular matrix specifically expressed by hypertrophic chondrocytes, was greatly reduced in the condylar cartilage of homozygous PTHrP-knockout mice compared with wild-type mice. In contrast, immunolocalization of type X collagen of the tibial cartilage did not differ. In wild-type mice, proliferative chondrocytes were mainly located in both the flattened cell layer and hypertrophic cell layer of the condylar cartilage, but were limited to the proliferative zone of the tibial cartilage. The number of proliferative chondrocytes was greatly reduced in both cartilages of homozygous PTHrP-knockout mice. Moreover, apoptotic chondrocytes were scarcely observed in the condylar hypertrophic cell layer, whereas a number of apoptotic chondrocytes were found in the tibial hypertrophic zone. Expression of the type I PTH/PTHrP receptor was localized in the flattened cell layer and hypertrophic cell layer of the condylar cartilage, but was absent from the tibial hypertrophic chondrocytes. It is therefore concluded that, unlike tibial hypertrophic chondrocytes, condylar hypertrophic chondrocytes have proliferative activity in the late embryonic stage, and PTHrP plays a pivotal role in regulating the proliferative capacity and differentiation of these cells.