bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth Without Growth Hormone Receptor: Estradiol Is a Major Growth Hormone-Independent Regulator of Hepatic IGF-I Synthesis
Authors: Venken Katrien , Schuit Frans , Van Lommel Leentje , Tsukamoto Katsura , Kopchick John J , Coschigano Karen , Ohlsson Claes , Movérare Sofia , Boonen Steven , Bouillon Roger , Vanderschueren Dirk 
Published: April 2006

Abstract
The role of estrogens in the regulation of pubertal growth independently of GH and its receptor was studied in male mice with disrupted GHRKO. E2 rescued skeletal growth rates in GHRKO associated with an increase in hepatic and serum IGF-I. These data show that E2 rescues pubertal growth during GH resistance through a novel mechanism of GHR-independent stimulation of hepatic IGF-I production.
Introduction: Growth hormone (GH) and estrogen play a pivotal role in pubertal growth and bone mineral acquisition. Estrogens can affect GH secretion and thereby provide a GH-dependent mechanism for their effects on skeletal growth. It is presently unclear if or to what extent estrogens are able to regulate pubertal growth and bone mineral accrual independently of GH and its receptor.
Materials and Methods: Estradiol (E2; 0.03 μg/day by subcutaneous silastic implants) was administered to orchidectomized (ORX) male mice with disrupted GHR (GHRKO) and corresponding WTs during late puberty (6–10 weeks). Longitudinal and radial bone growth, IGF-I in serum and its expression in liver, muscle, and bone, and liver gene expression were studied by histomorphometry, RIA, RT-PCR, microarrays, and Western blotting, respectively.
Results: E2 stimulated not only longitudinal (femur length and growth plate thickness) and radial growth (cortical thickness and periosteal perimeter), but also rescued longitudinal and periosteal growth rates in ORX GHRKO, whereas no significant changes occurred in WT. E2 thereby upregulated serum IGF-I and liver IGF-I synthesis (+21% and +52%, respectively) in ORX GHRKO, whereas IGF-I synthesis in femur or muscle was unaffected. Study of the underlying mechanism of the stimulation of hepatic IGF-I expression showed that E2 restored downregulated receptor signaling systems, such as the estrogen receptor α and the prolactin receptor. E2 thereby recovered the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway as evidenced by a significantly increased activation of the transcription factor STAT5 in ORX GHRKO.
Conclusions: Our data show a stimulation of skeletal growth through upregulation of hepatic IGF-I by a hormone other than GH. E2 rescues pubertal skeletal growth during GH resistance through a novel mechanism of GHR-independent stimulation of IGF-I synthesis in the liver.
Histone Deacetylase Inhibitors Promote Osteoblast Maturation
Authors: Schroeder Tania M , Westendorf Jennifer J 
Published: April 2006

Abstract
HDIs are potential therapeutic agents for cancer and neurological diseases because of their abilities to alter gene expression, induce growth arrest or apoptosis of tumors cells, and stimulate differentiation. In this report, we show that several HDIs promote osteoblast maturation in vitro and in calvarial organ cultures.
Introduction: Histone deacetylase inhibitors (HDIs) are currently in phase I and II clinical trials as anticancer agents. Some HDIs are also commonly prescribed treatments for epilepsy and bipolar disorders. Although administered systemically, the effects of HDIs on osteoblasts and bone formation have not been extensively examined. In this study, we investigated the effect of histone deacetylase inhibition on osteoblast proliferation and differentiation.
Materials and Methods: MC3T3-E1 cells, calvarial-derived primary osteoblasts, and calvarial organ cultures were treated with various commercially available HDIs (trichostatin A [TSA], sodium butyrate [NaB], valproic acid [VPA], or MS-275). The effects of these inhibitors on cell proliferation, viability, cell cycle progression, Runx2 transcriptional activity, alkaline phosphatase production, and matrix mineralization were determined. Expression levels of osteoblast maturation genes, type I collagen, osteopontin, bone sialoprotein, and osteocalcin in response to TSA were measured by quantitative PCR.
Results: Concentrations of HDIs that caused hyperacetylation of histone H3 induced transient increases in osteoblast proliferation and viability but did not alter cell cycle profiles. These concentrations of HDIs also increased the transcriptional activity of Runx2. TSA accelerated alkaline phosphatase production in MC3T3-E1 cells and calvarial organ cultures. In addition, TSA accelerated matrix mineralization and the expression of osteoblast genes, type I collagen, osteopontin, bone sialoprotein, and osteocalcin in MC3T3-E1 cells.
Conclusions: These studies show that histone deacetylase activity regulates osteoblast differentiation and bone formation at least in part by enhancing Runx2-dependent transcriptional activation. Therefore, HDIs are a potentially new class of bone anabolic agents that may be useful in the treatment of diseases that are associated with bone loss such as osteoporosis and cancer.
Regulation of Osteoclast Apoptosis and Motility by Small GTPase Binding Protein Rac1
Authors: Fukuda Akira , Hikita Atsuhiko , Wakeyama Hidetoshi , Akiyama Toru , Oda Hiromi , Nakamura Kozo , Tanaka Sakae 
Published: April 2006

Abstract
The role of Rac1 in osteoclast survival and bone-resorbing activity was examined using adenovirus vector expression systems. Rac1 is critically involved in M-CSF receptor signaling and mediates survival signaling primarily through PI3K/Akt pathways. Rac1 also plays a significant role in bone resorptive activity, probably by regulating the motility of osteoclasts.
Introduction: Rac1 is a member of Rho family small G-proteins, and recent studies have revealed that it mediates anti-apoptotic signals in some types of cells. Rac1 is reported to be required for the cytoskeletal organization and bone-resorbing activity of osteoclasts, but their roles in osteoclast survival and function are not fully elucidated.
Materials and Methods: We constructed the adenovirus vector carrying cDNA of either the dominant negative Rac1 (Rac1DN) or constitutively active Rac1 (Rac1CA) gene, and osteoclast-like cells (OCLs) generated in mouse co-culture system were infected with these viruses. To examine the role of Rac1 in osteoclast survival and function, we performed pit formation assays, survival assays, and Western blotting, including an activated-Rac1 pull-down assay using adenovirus-infected OCLs. To further clarify the mechanism of Rac1 regulation in osteoclast survival, some specific inhibitors and adenovirus vectors of signal transduction molecules were used. To quantify membrane movement before and after macrophage colony-stimulating factor (M-CSF) treatment, OCLs expressing either enhanced green fluorescent protein (EGFP) or Rac1DN were recorded with a time-lapse video microscope.
Results: Adenovirus vector-mediated dominant negative Rac1 (Rac1DN) expression significantly reduced pit formation, and promoted their apoptosis. M-CSF rapidly activated Rac1, and the prosurvival effect of M-CSF for OCLs was abrogated by Rac1DN overexpression. Constitutively active Rac1 enhanced OCL survival, which was completely suppressed by phosphatidylinositol 3′-kinase (PI3K) inhibitors, whereas a Mek inhibitor had only partial effect. Rac1DN also partially blocked the activation of Akt induced by the overexpressing catalytic subunit of PI3K. Using time-lapse video microscopy, we found that Rac1DN expression reduced membrane ruffling and the spreading of OCLs in response to M-CSF.
Conclusions: Small guanosine triphosphatase (GTPase) Rac1 is critically involved in M-CSF receptor signaling and mediates survival signaling of osteoclasts primarily by modulating PI3K/Akt pathways. Rac1 also plays a significant role in the bone resorptive activity of cells, probably by regulating the motility of osteoclasts.
Genetic Background Influences Cortical Bone Response to Ovariectomy
Authors: Li Chao Yang , Schaffler Mitchell B , Wolde-Semait Henock T , Hernandez Christopher J , Jepsen Karl J 
Published: April 2006

Abstract
Peak bone mass is genetically determined, but little is known about the heritability of bone loss. Inbred mice were ovariectomized at 16 weeks of age and killed at three time-points after surgery. We found that the variation in estrogen deficit-related cortical bone loss is genetically determined.
Introduction: Variability in adult bone morphology and composition among three inbred mouse strains—A/J, C57BL/6J (B6), and C3H/HeJ (C3H)—suggests that they gain bone in different ways during growth. In this study, we tested the hypothesis that these strains would also lose bone differently after estrogen deprivation.
Materials and Methods: Female A/J, B6, and C3H mice (N = 70/strain) were either ovariectomized (OVX) or sham-operated at 16 weeks of age and killed at 4, 8, and 16 weeks after surgery. Cortical bone histomorphometry was performed on right femoral mid-diaphyseal cross-sections. Mechanical properties were determined by loading left femoral mid-diaphyses to failure in four-point bending.
Results: Both OVX-A/J and OVX-B6 mice showed a 7–8% decrease in cortical area and width because of an 8–10% marrow expansion at 16 weeks after OVX. This bone loss did not affect mechanical properties in OVX-A/J femurs, but maximum load and stiffness in OVX-B6 decreased slightly (9%) at 4 and 8 weeks, and markedly (14–19%) at 16 weeks after OVX. In contrast, OVX-C3H showed a significant decrease in cortical area and width (6–7%) at 4 weeks after OVX and a slight decrease in the subperiosteal area (4%) at 8 weeks after OVX, although marrow area remained unchanged. Surprisingly, intracortical resorption spaces, which were present in sham-C3H mice, were greatly increased (+195%) in OVX-C3H mice at 8 weeks after OVX. Bone strength and stiffness in OVX-C3H mice decreased markedly (12–14%) at 4 weeks but slightly (8–10%) at 8 weeks after OVX. All indices except intracortical pore area in OVX-C3H mice returned to sham levels at 16 weeks after OVX.
Conclusions: The magnitude, timing, and location of cortical bone loss after OVX varied significantly among A/J, B6, and C3H mice. The subsequent changes in mechanical properties after OVX depended on the variable bone patterns as well as the size and shape of the adult bone. Our results suggest that patterns of estrogen deficit-associated cortical bone loss are genetically determined.
Bone and Body Composition of Children and Adolescents With Repeated Forearm Fractures
Authors: Goulding Ailsa , Grant Andrea M , Williams Sheila M 
Published: April 2006

Abstract
DXA measurements in 90 children and adolescents with repeated forearm fractures showed reduced ultradistal radius BMC and BMD values and elevated adiposity, suggesting site-specific bone weakness and high body weight increase fracture risk. Symptoms to cow milk, low calcium intakes, early age of first fracture, and overweight were over-represented in the sample.
Introduction: Although many apparently healthy children fracture their forearms repeatedly during growth, no previous studies of their bone health and body composition have been undertaken. Nor has the prevalence of established risk factors for fracture in such a population been assessed.
Materials and Methods: Ninety children and adolescents (47 girls and 43 boys) 5–19 years of age, who had experienced at least two fractures of the forearm, were studied. Bone size and mineralization were assessed using DXA at the ultradistal radius, one-third radius, neck of femur, hip trochanter, lumbar spine, and total body. Total body lean mass and fat mass were also determined. The prevalence of six risk factors for fracture were also examined, and their influence on ultradistal BMC Z scores was assessed.
Results: Participants experienced 295 fractures (74.9% forearm). Children with an early age of first fracture had higher rates of fracture per l00 years of exposure than those fracturing later. Four risk factors for fracture were over-represented in observed versus expected percentages: early age of first fracture (27.7% versus 11.3%), adverse symptoms to cow milk (22.2% versus 6.7%), low dietary calcium intake (20% versus 4.5%), and overweight (33.3% versus 15.5%). However, physical activity levels were similar to the reference population. Z scores for BMC and BMD were reduced, particularly at the ultradistal radius, whereas Z scores for weight, body mass index, fat mass, and body fat percentage were increased. Mean (SD) BMC Z scores were lowest at the ultradistal radius, −0.66 (1.22), where symptoms to milk were associated with reduced values (p &lt; 0.009) and overweight with increased values (p &lt; 0.003).
Conclusions: Our results suggest site-specific weakness and high body weight contribute to fracture risk in children and adolescents who fracture their forearms repeatedly. These findings are consonant with work showing adult Colles fractures increase as ultradistal radius BMD falls and with evidence that overweight children and adolescents are fracture prone.
Multiple Mechanisms Are Involved in Inhibition of Osteoblast Differentiation by PTHrP and PTH in KS483 Cells
Authors: van der Horst Geertje , Farih-Sips Hetty , Löwik Clemens WGM , Karperien Marcel 
Published: April 2006

Abstract
We examined the mechanism by which PTHrP and PTH inhibit KS483 osteoblastic differentiation. We show that PTHrP and PTH inhibit differentiation downstream of early BMP signaling and downregulated components of the hedgehog (Hh) signaling cascade. In addition, PTHrP and PTH repressed RunX2 and osx expression. Overexpression of either gene, however, could not relieve PTHrP and PTH's inhibitory actions. Our data suggest that multiple parallel mechanisms are involved in the inhibition of osteoblast differentiation and matrix mineralization by PTHrP and PTH.
Introduction: PTH-related peptide (PTHrP) and PTH are potent inhibitors of osteoblast differentiation in vitro by as yet unexplained mechanisms.
Materials and Methods: We treated murine bone marrow stromal cells and the mesenchymal progenitor cell line KS483 with PTHrP and PTH in combination with either BMPs or hedgehog (Hh) and measured early and late markers of osteoblast differentiation and studied the expression of RunX2 and Osterix (osx). In addition, we examined the PTHrP and PTH response in stable KS483 cells overexpressing either RunX2 or osx.
Results: PTHrP and PTH inhibited BMP- and Hh-induced osteogenesis downstream of early BMP signaling and by downregulation of components of the Hh signaling cascade. PTHrP and PTH prevented the upregulation of RunX2 expression associated with osteoblast differentiation in an indirect response. However, PTHrP and PTH could still inhibit differentiation, and particularly matrix mineralization, of cells expressing RunX2. In addition, PTHrP and PTH potently downregulated osx expression only in mature osteoblasts in an intermediate early response, but osx overexpression could not relieve the inhibitory effects of PTHrP and PTH on matrix mineralization.
Conclusions: Our data suggest that, besides transcriptional repression of RunX2 and osx, other mechanisms in parallel with or downstream of RunX2 and osx are involved in the inhibition of osteoblast differentiation and matrix mineralization by PTHrP and PTH in vitro.
A Nonprostanoid EP4 Receptor Selective Prostaglandin E2 Agonist Restores Bone Mass and Strength in Aged, Ovariectomized Rats
Authors: Ke Hua Zhu , Crawford D Todd , Qi Hong , Simmons Hollis A , Owen Thomas A , Paralkar Vishwas M , Li Mei , Lu Bihong , Grasser William A , Cameron Kimberly O , Lefker Bruce A , DaSilva-Jardine Paul , Scott Dennis O , Zhang Qing , Tian Xiao Yan , Jee Webster SS , Brown Thomas A , Thompson David D 
Published: April 2006

Abstract
CP432 is a newly discovered, nonprostanoid EP4 receptor selective prostaglandin E2 agonist. CP432 stimulates trabecular and cortical bone formation and restores bone mass and bone strength in aged ovariectomized rats with established osteopenia.
Introduction: The purpose of this study was to determine whether a newly discovered, nonprostanoid EP4 receptor selective prostaglandin E2 (PGE2) agonist, CP432, could produce bone anabolic effects in aged, ovariectomized (OVX) rats with established osteopenia.
Materials and Methods: CP432 at 0.3, 1, or 3 mg/kg/day was given for 6 weeks by subcutaneous injection to 12-month-old rats that had been OVX for 8.5 months. The effects on bone mass, bone formation, bone resorption, and bone strength were determined.
Results: Total femoral BMD increased significantly in OVX rats treated with CP432 at all doses. CP432 completely restored trabecular bone volume of the third lumbar vertebral body accompanied with a dose-dependent decrease in osteoclast number and osteoclast surface and a dose-dependent increase in mineralizing surface, mineral apposition rate, and bone formation rate-tissue reference in OVX rats. CP432 at 1 and 3 mg/kg/day significantly increased total tissue area, cortical bone area, and periosteal and endocortical bone formation in the tibial shafts compared with both sham and OVX controls. CP432 at all doses significantly and dose-dependently increased ultimate strength in the fifth lumber vertebral body compared with both sham and OVX controls. At 1 and 3 mg/kg/day, CP432 significantly increased maximal load in a three-point bending test of femoral shaft compared with both sham and OVX controls.
Conclusions: CP432 completely restored trabecular and cortical bone mass and strength in established osteopenic, aged OVX rats by stimulating bone formation and inhibiting bone resorption on trabecular and cortical surfaces.
Infant Growth Influences Proximal Femoral Geometry in Adulthood
Authors: Javaid M Kassim , Lekamwasam Sarath , Clark Judith , Dennison Elaine M , Syddall Holly E , Loveridge Nigel , Reeve Jonathan , Beck Tom J , Cooper Cyrus 
Published: April 2006

Abstract
The relationship between early growth and adult femoral geometry has not been studied previously. In 333 adults, we were able to show that infant weight predicts femoral width and cross-sectional moment of inertia but not femoral neck length. These results support the hypothesis that growth in early life leads to persisting differences in proximal femoral geometry.
Introduction: Both femoral geometry and bone mass have been shown independently to predict both hip strength and fracture risk. Whereas growth during intrauterine and early postnatal life has been shown to influence adult bone mass, the relationship between growth in early life and adult femoral geometry has not been described previously.
Materials and Methods: We studied the relationship between growth during early life, adult hip geometry, and proximal femur bone mass in a sample of 333 men and women (60–75 years of age), for whom birth weight and weight at 1 year of age were recorded. Hip geometry was derived using Hip Structure Analysis software from proximal femur DXA scans (Hologic QDR 1000).
Results: There were significant (p &lt; 0.002) relationships between weight at age 1 year and measures of femoral width as well as intertrochanteric (IT) cross-sectional moment of inertia (CSMI), but not with femoral neck length. The relationships with measures of femoral width but not CSMI remained after adjusting for adult body weight and were independent of proximal femoral BMC.
Conclusions: These results support the hypothesis that different patterns of growth in utero and during the first year of life lead to persisting differences in proximal femoral geometry, thereby mediating in part the effects of early growth on risk of hip fracture in adulthood.
Relative Impact of Androgen and Estrogen Receptor Activation in the Effects of Androgens on Trabecular and Cortical Bone in Growing Male Mice: A Study in the Androgen Receptor Knockout Mouse Model
Authors: Venken Katrien , De Gendt Karel , Boonen Steven , Ophoff Jill , Bouillon Roger , Swinnen Johannes V , Verhoeven Guido , Vanderschueren Dirk 
Published: April 2006

Abstract
The relative importance of AR and ER activation has been studied in pubertal male AR knockout and WT mice after orchidectomy and androgen replacement therapy, either with or without an aromatase inhibitor. AR activation dominates normal trabecular bone development and cortical bone modeling in male mice. Moreover, optimal periosteal bone expansion is only observed in the presence of both AR and ER activation.
Introduction: Androgen receptor (AR)–mediated androgen action has traditionally been considered a key determinant of male skeletal growth. Increasing evidence, however, suggests that estrogens are also essential for normal male bone growth. Therefore, the relative importance of AR-mediated and estrogen receptor (ER)–mediated androgen action after aromatization remains to be clarified.
Materials and Methods: Trabecular and cortical bone was studied in intact or orchidectomized pubertal AR knockout (ARKO) and male wildtype (WT) mice, with or without replacement therapy (3–8 weeks of age). Nonaromatizable (dihydrotestosterone [DHT]) and aromatizable (testosterone [T]) androgens and T plus an aromatase inhibitor (anastrazole) were administered to orchidectomized ARKO and WT mice. Trabecular and cortical bone modeling were evaluated by static and dynamic histomorphometry, respectively.
Results: AR inactivation or orchidectomy induced a similar degree of trabecular bone loss (−68% and −71%, respectively). Both DHT and T prevented orchidectomy-induced bone loss in WT mice but not in ARKO mice. Administration of an aromatase inhibitor did not affect T action on trabecular bone. AR inactivation and orchidectomy had similar negative effects on cortical thickness (−13% and −8%, respectively) and periosteal bone formation (−50% and −26%, respectively). In orchidectomized WT mice, both DHT and T were found to stimulate periosteal bone formation and, as a result, to increase cortical thickness. In contrast, the periosteum of ARKO mice remained unresponsive to either DHT or T. Interestingly, administration of an aromatase inhibitor partly reduced T action on periosteal bone formation in orchidectomized WT mice (−34% versus orchidectomized WT mice on T), but not in ARKO mice. This effect was associated with a significant decrease in serum IGF-I (−21% versus orchidectomized WT mice on T).
Conclusions: These findings suggest a major role for AR activation in normal development of trabecular bone and periosteal bone growth in male mice. Moreover, optimal stimulation of periosteal growth is only obtained in the presence of both AR and ER activation.