bluuebunny/crossref_metadata_2025_split huggingface dataset:
Osteocyte Apoptosis Is Induced by Weightlessness in Mice and Precedes Osteoclast Recruitment and Bone Loss
Authors: Aguirre J Ignacio , Plotkin Lilian I , Stewart Scott A , Weinstein Robert S , Parfitt A Michael , Manolagas Stavros C , Bellido Teresita 
Published: April 2006

Abstract
Mechanical stimulation of cultured osteocytic cells attenuates their apoptosis. We report here that, conversely, reduced mechanical forces in the murine model of unloading by tail suspension increases the prevalence of osteocyte apoptosis, followed by bone resorption and loss of mineral and strength.
Introduction: Mechanical loading is critical for the maintenance of bone mass; weightlessness, as with reduced physical activity in old age, bed rest, or space flight, invariably leads to bone loss. However, the cellular and molecular mechanisms responsible for these phenomena are poorly understood. Based on our earlier findings that physiologic levels of mechanical strain prevent apoptosis of osteocytic cells in vitro, we examined here whether, conversely, reduced mechanical forces increase the prevalence of osteocyte apoptosis in vivo and whether this event is linked to bone loss.
Materials and Methods: Swiss Webster mice or OG2-11β-hydroxysteroid dehydrogenase type 2 (OG2-11β-HSD2) transgenic mice and wildtype littermates were tail-suspended or kept under ambulatory conditions. Static and dynamic histomorphometry and osteocyte and osteoblast apoptosis by in situ end-labeling (ISEL) were assessed in lumbar vertebra; spinal BMD was measured by DXA; and bone strength was measured by vertebral compression.
Results: We show that within 3 days of tail suspension, mice exhibited an increased incidence of osteocyte apoptosis in both trabecular and cortical bone. This change was followed 2 weeks later by increased osteoclast number and cortical porosity, reduced trabecular and cortical width, and decreased spinal BMD and vertebral strength. Importantly, whereas in ambulatory animals, apoptotic osteocytes were randomly distributed, in unloaded mice, apoptotic osteocytes were preferentially sequestered in endosteal cortical bone—the site that was subsequently resorbed. The effect of unloading on osteocyte apoptosis and bone resorption was reproduced in transgenic mice in which osteocytes are refractory to glucocorticoid action, indicating that stress-induced hypercortisolemia cannot account for these effects.
Conclusions: We conclude that diminished mechanical forces eliminate signals that maintain osteocyte viability, thereby leading to apoptosis. Dying osteocytes in turn become the beacons for osteoclast recruitment to the vicinity and the resulting increase in bone resorption and bone loss.
Cellular Activity on the Seven Surfaces of Iliac Bone: A Histomorphometric Study in Children and Adolescents
Authors: Rauch Frank , Travers Rose , Glorieux Francis H 
Published: April 2006

Abstract
Transiliac cortical bone histomorphometry was performed in 56 metabolic bone disease-free individuals 1.5–22.9 years of age. During the growing years, the two cortices of an iliac bone specimen differ with regard to bone cell activity on their surfaces, probably reflecting a modeling drift.
Introduction: Standard bone histomorphometry in the clinical setting is typically limited to the analysis of cancellous bone. However, during the growth period, important changes occur also in the cortical compartment.
Materials and Methods: Transiliac bone samples from 56 individuals between 1.5 and 22.9 years of age (25 male; tetracycline labeling present in 42 subjects) and without evidence of metabolic bone disease were analyzed. Each of the three bone surface types (periosteal, intracortical, endocortical) of each cortex was evaluated separately. Results were expressed relative to those obtained in trabecular bone.
Results: A significant increase in cortical width with age was detected only for the internal cortex. Porosity of the external cortex was highest in the 7- to 10.9-year age group and decreased thereafter, whereas there was no clear trend with age for the porosity of the internal cortex. Intracortical remodeling activity decreased after 14 years of age. Periosteal bone formation was very active until 13 years of age, but was close to zero in subjects above that age. As to endocortical surfaces, all bone surface-based parameters of bone formation were higher on the internal cortex than on the external cortex, whereas bone resorption parameters were higher on the external cortex.
Conclusions: In growing subjects, the two cortices of an iliac bone specimen differ with regard to bone cell activity on their surfaces. These data raise fundamental questions about the regulation of bone cell activity in children and adolescents.
Free Testosterone is an Independent Predictor of BMD and Prevalent Fractures in Elderly Men: MrOS Sweden
Authors: Mellström Dan , Johnell Olof , Ljunggren Östen , Eriksson Anna-Lena , Lorentzon Mattias , Mallmin Hans , Holmberg Anna , Redlund-Johnell Inga , Orwoll Eric , Ohlsson Claes 
Published: April 2006

Abstract
The role of androgens for bone health in elderly men is unclear. We show that free testosterone within the normal range is a predictor of BMD at predominantly cortical bone sites and of previous osteoporosis-related fractures in elderly Swedish men.
Introduction: Osteoporosis-related fractures constitute a major health concern not only in women but also in men. Previous studies have clearly shown that serum levels of estradiol are associated with BMD, whereas more conflicting data have been presented regarding the predictive value of testosterone (T) for bone health in elderly men. The aim of this study was to investigate if serum levels of T are associated with BMD and/or prevalent fractures in a large cohort of elderly men.
Materials and Methods: In the Swedish part of the MrOS study (n = 2908; average age, 75.4 years), bone parameters were measured using DXA, and prevalent fractures were recorded using standardized questionnaires and by vertebral X-ray analyses. Serum levels of total T, total estradiol (E2), and sex hormone–binding globulin (SHBG) were measured by radioimmunoassay, and free T (FT) and free E2 (FE2) were derived from the mass action equations. Height, weight, age, physical activity, smoking habits, and calcium intake were included together with FT and FE2 in regression models for BMD.
Results: FT was an independent positive predictor of BMD in total body, total hip, femur trochanter, and arm but not in the lumbar spine. The highest independent predictive value of FT was found in the arm and the hip (with a relatively high content of cortical bone). FE2 was an independent predictor of BMD at all bone sites studied, and the highest predictive value was seen for lumbar spine (with relatively high content of trabecular bone) BMD. FT but not FE2 was a positive predictor of total body bone area and BMC. FT levels below the median were independent predictors of prevalent osteoporosis-related fractures (OR, 1.56; 95% CI, 1.14–2.14; p &lt; 0.01) and X-ray–verified vertebral fractures (OR, 2.00; 95% CI, 1.34–2.86; p &lt; 0.001). The predictive value of FT for prevalent fractures was not affected by adjustment for BMD.
Conclusions: These findings show that variation of FT within the normal range is an independent but modest predictor of BMD at predominantly cortical bone sites and of previous osteoporosis-related fractures in elderly men. Our data indicate that not only estrogens but also androgens are of importance for bone health in elderly men. Longitudinal studies investigating the predictive value of T for fracture risk in elderly men are required.
Increased Prevalence of Radiological Spinal Deformities in Adult Patients With GH Deficiency: Influence of GH Replacement Therapy
Authors: Mazziotti Gherardo , Bianchi Antonio , Bonadonna Stefania , Nuzzo Monica , Cimino Vincenzo , Fusco Alessandra , De Marinis Laura , Giustina Andrea 
Published: April 2006

Abstract
This cross-sectional study shows that a high number of untreated adult patients with GHD develop radiological vertebral deformities. Patients undergoing GH replacement treatment showed a significantly lower prevalence of vertebral deformities versus treated patients in the presence of similar BMD, as assessed by DXA.
Introduction: In this cross-sectional study, we investigated whether the prevalence and degree of spinal deformities in adults with growth hormone deficiency (GHD) were related to the age of patients, degree of bone turnover, BMD, and recombinant human GH (rhGH) replacement therapy.
Materials and Methods: One hundred seven adult hypopituitary patients (67 males and 40 females; mean age, 47 years; range: 16–81 years) with severe GHD and 130 control subjects (39 males, 91 females; mean age: 58.9 years; range: 26–82 years) were evaluated for BMD (DXA) and vertebral deformities (quantitative morphometric analysis). At study entry, 65 patients were on replacement therapy with rhGH, whereas 42 patients had never undergone rhGH.
Results: Vertebral fractures were significantly more frequent in GHD patients versus control subjects (63.6% versus 37.7%; χ2 15.7; p &lt; 0.001). The fracture prevalence, as well as the fracture number, was significantly higher in untreated versus treated patients (78.6% versus 53.8%; χ2: 6.7; p = 0.009), although the two groups of patients did not show any significant difference in median T score. In untreated GHD patients, the prevalence of vertebral deformities was correlated with T score (p = 0.002) and duration of disease (p = 0.003). In treated GHD patients, the prevalence of spinal deformities was correlated only with the timing of the beginning of rhGH replacement.
Conclusions: This cross-sectional study reports high prevalence of vertebral radiological deformities in adult patients with untreated GHD. The replacement treatment of GHD leads to a significant decrease in fracture rate.
Nuclear Matrix Proteins and Osteoblast Gene Expression
Authors: Bidwell Joseph P. , Alvarez Marta , Feister Hilary , Onyia Jude , Hock Janet 
Published: April 2006

Abstract
The molecular mechanisms that couple osteoblast structure and gene expression are emerging from recent studies on the bone extracellular matrix, integrins, the cytoskeleton, and the nucleoskeleton (nuclear matrix). These proteins form a dynamic structural network, the tissue matrix, that physically links the genes with the substructure of the cell and its substrate. The molecular analog of cell structure is the geometry of the promoter. The degree of supercoiling and bending of promoter DNA can regulate transcriptional activity. Nuclear matrix proteins may render a change in cytoskeletal organization into a bend or twist in the promoter of target genes. We review the role of nuclear matrix proteins in the regulation of gene expression with special emphasis on osseous tissue. Nuclear matrix proteins bind to the osteocalcin and type I collagen promoters in osteoblasts. One such protein is Cbfa1, a recently described transcriptional activator of osteoblast differentiation. Although their mechanisms of action are unknown, some nuclear matrix proteins may act as “architectural” transcription factors, regulating gene expression by bending the promoter and altering the interactions between other trans-acting proteins. The osteoblast nuclear matrix is comprised of cell- and phenotype-specific proteins including proteins common to all cells. Nuclear matrix proteins specific to the osteoblast developmental stage and proteins that distinguish osteosarcoma from the osteoblast have been identified. Recent studies indicating that nuclear matrix proteins mediate bone cell response to parathyroid hormone and vitamin D are discussed.
Gene Expression of Bone Matrix Proteins and Endothelin Receptors in Endothelin-1–Deficient Mice Revealed by In Situ Hybridization
Authors: Kitano Yukie , Kurihara Hiroki , Kurihara Yukiko , Maemura Koji , Ryo Yoshimi , Yazaki Yoshio , Harii Kiyonori 
Published: April 2006

Abstract
Endothelin-1 (ET-1) was first found as a vasoconstrictor protein excreted by vascular endothelial cells, but recently ET-1 has been considered to have widespread functions that include regulation of osteochondrogenic metabolism. We analyzed sections of head regions in ET-1 knockout mice that are known to have abnormalities in pharyngeal arch–derived tissues and found that there was severe hypoplasia in facial bones. The hypoplasia suggests that the matrix mineralization system of facial bones is disrupted in ET-1−/− homozygous mice. To elucidate whether osteogenic cells in facial bones are the targets for ET-1 and whether expression of bone matrix genes are modulated by ET-1, we examined gene expression of ET-1 receptors, ETA and ETB, and that of the bone matrix proteins, osteonectin (ON) and osteopontin (OP), both in the head regions of ET-1+/− heterozygous and ET-1−/− homozygous mice by means of in situ hybridization. Different patterns of expression between ETA and ETB mRNAs were observed in both groups. In 18.5 days post coitus fetuses, ETA mRNA was most strongly expressed in osteogenic cells along craniofacial bones, but ETB mRNA was most strongly expressed in trunks of trigeminal nerve. This finding suggests that ET-1 may modulate osteogenic cells through ETA receptor but not through ETB receptor. The expression patterns of ETA, OP, and ON mRNAs were distinct between the two groups. In the lower jaw of ET-1+/− heterozygous mice, the ETA, ON, and OP mRNA positive cells were scattered in the inner and outer regions of the thick bone matrix, but in ET-1−/− homozygous mice, cells containing those mRNAs were located close to each other at the surface of thin bone matrix. However, cellular expression of ON and OP mRNAs in osteogenic cells of ET-1−/− homozygous mice was not suppressed as compared with ET-1+/− heterozygous mice. We conclude that ET-1 may regulate proliferation and migration of osteogenic cells in the maxillofacial region, rather than modulating the expression level of ON and OP mRNAs.
Intestinal Calcium Absorption and Bone Metabolism in Young Adult Men with Childhood-Onset Growth Hormone Deficiency
Authors: De Boer Hans , Blok Geert Jan , Popp-Snijders Corrie , Sips Adriënne , Lips Paul , Van Der Veen Eduard 
Published: April 2006

Abstract
Suboptimal growth hormone (GH) replacement therapy during childhood is a major cause of osteopenia in young adults with childhood-onset GH deficiency (CO-GHD). This is primarily attributed to reduced bone formation in childhood. It is currently not known whether GHD also has adverse effects on bone metabolism in adult life. To examine the impact of GHD on calcium and bone metabolism in adults, we evaluated 50 men with CO pituitary failure at a mean age of 28.2 ± 4.5 years, i.e., 8.8 ± 4.1 years after the discontinuation of previous GH treatment for short stature. Thirty-three patients had multiple pituitary hormone deficiencies (MPHD) for which they received conventional replacement therapy, seventeen patients had isolated GHD (IGHD), and forty-nine age-matched men served as controls. Intestinal calcium absorption, serum calcium concentration, serum phosphate levels, and renal calcium and phosphate excretion were normal in IGHD and MPHD patients. IGHD patients had marginally elevated serum levels of the carboxy-terminal cross-linked telopeptide of type I collagen (ICTP: 5.0 ± 1.2 vs. 4.2 ± 1.2 μg/l, p &lt; 0.05), but other indices of bone turnover were normal. In contrast, MPHD patients had reduced levels of the carboxy-terminal propeptide of type I procollagen (PICP: 137 ± 76 vs. 179 ± 72 μg/l, p &lt; 0.01), elevated serum ICTP levels (6.0 ± 3.8 vs. 4.2 ± 1.2 μg/l, p &lt; 0.001), and reduced serum 1,25-dihydroxyvitamin D levels (55.1 ± 16.7 vs. 73.0 ± 23.0 pmol/l, p &lt; 0.001). Multivariate regression analysis showed that the serum levels of bone resorption and bone formation markers in MPHD patients were correlated with the hydrocortisone, thyroxine, and testosterone replacement doses. There was no relationship with serum insulin-like growth factor I concentration. Panhypopituitary adults receiving conventional hormone replacement therapy are at risk to develop osteopenia either caused by reduced bone formation or by increased bone resorption activity. Predominantly, these abnormalities result from nonoptimal thyroid, gonadal, or adrenal hormone replacement therapy. GHD is not an important factor. In adults, GHD does not adversely affect intestinal calcium absorption or bone formation activity. Bone resorption activity may be slightly higher than normal, but the abnormality is too small to expect substantial bone loss as a consequence of GHD.
Apatite Induction by Insoluble Dentin Collagen
Authors: Saito Takashi , Yamauchi Mitsuo , Crenshaw Miles A. 
Published: April 2006

Abstract
Phosphoproteins are thought to play a role in mineral formation in dentin. A portion of this phosphoprotein is bound to collagen. We have investigated the requirement for bound phosphate in mineral induction by isolated dentin collagen. Insoluble bovine dentin collagen obtained by ethylene-diamino-tetra-acetic acid (EDTA) demineralization had 19.5 mol of P/mol of collagen that could not be extracted with 0.5 M EDTA in 4 M guanidine HCl. When this collagen was incubated in supersaturated solutions that did not spontaneously precipitate, apatite was induced. With progressive enzymatic dephosphorylation, induction times for mineral formation became progressively longer. The dentin did not induce mineral formation when 90% of the ester phosphate was removed. Insoluble bone collagen, which had even less phosphate, also did not induce mineral formation. Mineral induction times by dentin collagen increased with decreasing solution saturations. Using these data, the interfacial tension for mineral induction was determined to be 90 ergs/cm2. This value approximated that of phosphatidic acid liposomes and of phosvitin cross-linked to agarose beads, and it might reflect the energetics of heterogeneous nucleation on a highly phosphorylated surface. Sequestering of calcium-phosphate clusters on the phosphoprotein probably accounts for the observed calcium binding by dentin collagen in excess of that required to neutralize the phosphate esters of the collagen. Because the phosphoprotein is immobilized at a low density on the collagen, it cannot self-associate in calcium-phosphate solutions as it does when it is free in solution. This immobilized phosphoprotein allows the mineral clusters formed on its surface to grow into a crystalline order.
Impaired Expression of Noncollagenous Bone Matrix Protein mRNAs During Fracture Healing in Ascorbic Acid–Deficient Rats
Authors: Sugimoto Mizuo , Hirota Seiichi , Sato Motohiko , Kawahata Hirohisa , Tsukamoto Ikuyo , Yasui Natsuo , Kitamura Yukihiko , Ochi Takahiro , Nomura Shintaro 
Published: April 2006

Abstract
In scorbutic patients, fractures are slow to heal because of impaired collagen synthesis. To investigate the influence of impaired collagen synthesis on the differentiation and proliferation of osteogenic and chondrogenic cells, we examined the expression of genes encoding bone matrix proteins, including osteonectin (ON), osteopontin (OPN), osteocalcin (OC), and matrix Gla protein (MGP), as differentiation markers for osteogenic and chondrogenic cells during fracture healing in Osteogenic Disorder Shionogi (ODS) rats, which have a hereditary defect in the ability to synthesize ascorbic acid (Asc). In ODS rats without Asc supplementation, intramembranous ossification was completely inhibited. Although a few fibroblast-like cells expressing ON mRNA were observed, no OPN mRNA-expressing cells were detected. During endochondral ossification, a small amount of metachromatic staining cartilage appeared at the fracture site, but there was no provisional calcification zone in the cartilage. Chondrocytes expressed ON and MGP mRNAs, but not OPN mRNA. When Asc was given to these rats, callus formation was soon detected around the fracture site, while OPN mRNA was expressed by differentiated osteoblasts and hypertrophic chondrocytes. Our data indicate that impaired collagen synthesis due to Asc deficiency inhibited the increase of ON and MGP mRNA-expressing cells as well as the appearance of OPN mRNA-expressing cells. Since OPN is considered to play an important role in normal and pathological mineralization, lack of OPN mRNA expression accompanying impaired collagen synthesis may have a role in defective mineralization and delayed fracture healing in scurvy.
Clodronate Prevents Osteopenia and Loss of Trabecular Connectivity in Estrogen-Deficient Rats
Authors: Kippo Katriina , Hannuniemi Ritva , Isaksson Päivi , Laurén Leena , Österman Thua , Peng Zhiqi , Tuukkanen Juha , Kuurtamo Pirjo , Väänänen H. Kalervo , Sellman Raija 
Published: April 2006

Abstract
Daily oral clodronate treatment was evaluated in Sprague-Dawley rats for its ability to inhibit estrogen-deficiency–induced changes in femoral neck, femoral diaphysis, and lumbar vertebrae (L4–L5). Six-month-old ovariectomized (OVX) rats were administered by gavage a vehicle (Veh) or clodronate (100 or 500 mg/kg/day). Sham-operated (SHAM) control rats received the vehicle (n = 15/group). Treatment was started on the day of operation and continued for 3 months. Trabecular bone volume (BV/TV) and structural variables (trabecular number, Tb.N; thickness, Tb.Th; separation, Tb.Sp; and trabecular bone pattern factor, Tb.Pf) were assessed on secondary spongiosa of the right femoral neck. Furthermore, cantilever bending test of the left femoral neck and compression test of L4, ash weight of L5, and morphometric studies of femoral diaphysis were carried out, and serum and urinary markers of bone turnover were determined. The OVX/Veh group had higher levels of serum osteocalcin and alkaline phosphatase and higher urinary excretion of deoxypyridinoline/creatinine than the SHAM/Veh group at 3 months postsurgery, and clodronate reduced these changes. BV/TV of femoral neck, bone mass of L5, and the maximum loads of the femoral neck and L4 were lower after OVX than SHAM operation. Although clodronate prevented trabecular bone loss in the femoral neck and preserved Tb.Pf at the SHAM control level, it failed to preserve the mechanical strength at the femoral neck. However, in lumbar vertebrae, clodronate prevented the loss of bone mass and mechanical properties. Furthermore, there was a good positive correlation between maximum load of L4 and the ash weight of L5 (n = 58, r = 0.69, p &lt; 0.001). In the femoral neck (n = 55), Tb.Pf correlated negatively with BV/TV and Tb.N (r = −0.59 and r = −0.55; p &lt; 0.001, respectively) and positively with Tb.Sp (r = 0.61, p &lt; 0.001). In femoral mid-diaphysis, there were no significant changes in cortical bone geometry in any of the groups. We conclude that orally administered clodronate suppresses the enhanced bone turnover in adult OVX rats and preserves trabecular bone volume and connectivity in the femoral neck. In the axial skeleton, clodronate has a beneficial effect on lumbar vertebral bone mass and strength.