bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modulation of responsiveness of the adenylate cyclase system in avian chondroprogenitor cells by pertussis toxin, PTH, and PGE2
Authors: Pines Mark , Yosif Bernard , Hurwitz Shmuel 
Published: February 2010

Abstract
Chondroprogenitor cells, derived from avian tibia epiphyseal growth plate, were cultured in vitro. Incubation of these cells with pertussis toxin augmented their cAMP response to parathyroid hormone (PTH), attenuated the response to forskolin, but did not modify the response to PGE2. Pertussis toxin modulation of the cAMP response was accompanied by ADP ribosylation of two proteins with molecular weights of 39 and 40 kD. Using specific antibodies, the 39 kD protein was identified as the inhibitory guanine nucleotide binding protein (Gi) of the adenylate cyclase system. The other ADP-ribosylated protein has not been identified.
Preincubation of the chondroprogenitor cells with PTH or PGE2 resulted in time-dependent heterologous desensitization of the cAMP response to a second challenge of either hormone. The cells did not recover from the densensitization for at least 18 h after removal of the hormones. PTH and PGE2 treatment did not affect the cAMP response to forskolin and cholera toxin. The PTH-dependent cAMP production was also not altered by forskolin treatment. PTH homologous desensitization was not affected by pertussis toxin treatment, but the heterologous desensitization due to PGE2 was significantly attenuated.
These results suggest that exposure of chondroprogenitor cells to PTH and PGE2 results in heterologous desensitization of the cAMP response. The desensitization is not due to changes in the adenylate cyclase activity. The pertussis toxin-sensitive G proteins are involved in the PTH heterologous rather than homologous desensitization of the cAMP response.
Expression of calcitonin receptors during osteoclast differentiation in mouse metatarsals
Authors: Taylor Linda M. , Tertinegg Inka , Okuda Ayako , Heersche Johannes N.M. 
Published: February 2010

Abstract
Metatarsal bones of 15-day-old mouse embryos contain proliferative tartrate-resistant acid phosphatase (TRAP) negative (-) osteoclast progenitors that progressively differentiate into multinucleated TRAP positive (+) osteoclasts. Using histochemical and autoradiographic techniques, we have examined the expression of calcitonin receptors during osteoclast differentiation in mouse metatarsals. Fresh mouse metatarsals from embryos aged 14–17 days and metatarsals from 15-day-old embryos cultured for 1, 2, 3, and 6 days were stained for TRAP. Calcitonin binding to osteoclasts and their precursors was studied by incubating metatarsals with [125I]salmon calcitonin (sCT) and quantitating grain counts from autoradiographs of tissue sections. Calcitonin receptors first appear on nonproliferating osteoclast precursors, most often just after or simultaneously with the development of TRAP activity. The effect of sCT on the development of TRAP+ mononuclear preosteoclasts was examined by culturing 15-day-old metatarsals in the continuous presence of 5 mU sCT for periods of up to 3 days and quantitating the number of TRAP+ mononuclear preosteoclasts that develop. Calcitonin did not affect the differentiation of osteoclasts up to the stage of the TRAP+ mononuclear preosteoclast.
Role of bone and kidney in parathyroid hormone-related peptide-induced hypercalcemia in rats
Authors: Rizzoli René , Caverzasio J. , Chapuy M.C. , Martin T.J. , Bonjour J.P. 
Published: February 2010

Abstract
A protein responsible for the biochemical syndrome similar to primary hyperparathyroidism associated with certain tumors has been recently characterized and its effects at the level of bone and kidney reported. However, the relative role of tubular reabsorption of calcium (Ca) and bone resorption in the pathogenesis of hypercalcemia induced by this factor is still debated. We investigated the effects of a synthetic amino-terminal fragment of parathyroid hormone-related protein [PTHrP-(1–34)] administered chronically by intraperitoneal osmotic minipumps in thyroparathyroidectomized (TPTX) rats. Clearance studies performed on day 6 of treatment after a 24 h fast revealed an increase in renal tubular reabsorption of Ca and a decrease in renal tubular reabsorption of phosphate (Pi), accompanied by an increase in cAMP excretion. PTHrP-(1–34) (90 pmol/h) stimulated bone resorption as evaluated by an increment in fasting urinary Ca excretion. Although the bone resorption inhibitor aminopropylidene diphosphonate fully corrected urinary Ca excretion and reduced plasma Ca from 3.04 ± 0.07 to 2.44 ± 0.21 mM (p &lt; 0.05), this latter value remained considerably higher than in TPTX control rats (1.54 ± 0.12 mM, p &lt; 0.01). In contrast, when the agent WR-2721, which is known to decrease the renal tubular reabsorption of Ca by a PTH-independent mechanism, was given, a further drop in plasma Ca and an increase in urinary Ca excretion were observed. These findings are similar to those found in animals implanted with the hypercalcemic Leydig cell tumor. In conclusion, this study indicates that stimulation of renal tubular reabsorption of Ca is an important determinant of the increase in plasma Ca induced by the chronic infusion of PTHrP-(1–34) in TPTX rats.
Protein kinase C activity in UMR-106-01 cells: Effects of parathyroid hormone and insulin
Authors: Iida-Klein Akiko , Varlotta Vicky , Hahn Theodore J. 
Published: February 2010

Abstract
The calcium and phospholipid-dependent protein kinase C (PKC) system appears to play an important role in mediating hormonal effects in various tissues including bone. Accordingly, we characterized PKC activity in the UMR-106–01 rat osteosarcoma osteoblastlike cell line and examined its hormonal regulation. UMR- 106–01 cells were found to possess a classic, phorbol ester-activated PKC system, which was highly calcium and phospholipid dependent. A 30 s exposure to 10 nM bovine parathyroid hormone (PTH) (1–34) increased cytosolic and membrane-bound PKC activity by 12 and 157%, respectively, resulting in a 2.2-fold increase in the membrane-bound to cytosolic (MB/C) activity ratio (all p &lt; 0.01). The MB/C activity ratio was highest at 20 min, exhibiting a 2.8-fold increase over the control values (p &lt; 0.01). In contrast, 10 nM insulin increased cytosolic PKC activity but decreased membrane-bound activity, resulting in a 61% decrease in the MB/C activity ratio at 20 min (p &lt; 0.02). Moreover, insulin reduced PTH stimulation of the PKC activity ratio by 42 and 62% at 30 s and 20 min, respectively (p &lt; 0.02). Thus, PTH and insulin have opposing effects on the PKC activity ratio in UMR-106–01 cells.
Influence of body habitus and race on bone mineral density of the midradius, hip, and spine in aging women
Authors: Desimone Daniel P. , Stevens June , Edwards Jeanne , Shary Judith , Gordon Leonie , Dr. Bell Norman H. 
Published: February 2010

Abstract
Osteoporosis and fractures of the hip are less common in black women and in obese white women than in nonobese white women. To determine the effects of race, age, and body weight on bone mineral density (BMD), BMD of the lumbar spine, trochanter, and femoral neck were determined by dual-photon absorptiometry in 131 nonobese white women and 34 nonobese black women, all of whom were within 30% of their ideal body weight, and in 24 obese white women and 27 obese black women, all of whom weighed more than 30% of their ideal body weight and were in the same age range as the nonobese women. All of them were 51 years of age or older, and most of them were postmenopausal. BMD of the midradius was measured by single-photon absorptiometry. Whereas body weight was significantly higher in the black as compared to the white women, the ages of the two groups were not different from each other. BMD declined with age and increased with body weight in both the black and white women at each of the four sites measured. After adjusting for age and weight by covariate analyses, black women had greater BMDs than white women at the midradius, lumbar spine, and femoral neck (p &lt; 0.001), but not at the trochanter (p = 0.18). The increases in BMD observed in the obese and black women in the present study are consistent with the previous findings that osteoporosis and fractures of the hip are less common in black and in obese white women than in nonobese white women.
The partial degradation of osteonectin by a bone-derived metalloprotease enhances binding to type I collagen
Authors: Dr. Tyree Bernadette 
Published: February 2010

Abstract
Cultured neonatal rat calvaria produce latent metalloproteases capable of degrading collagen, gelatin, and osteonectin. The osteonectin-degrading activity was further characterized and found to be optimally active between pH 6 and 8 and inhibited with EDTA and 1,10-phenanthroline but not phenylmethylsulfonyl fluoride. Analysis of the degradation products of osteonectin by SDS-PAGE in the presence of dithiothreitol showed the generation of a somewhat stable 32,000 mw cleavage product. Comparison of the binding properties of this cleavage product with intact osteonectin indicated that the fragment retained its ability to bind hydroxyapatite in the presence of high salt (2 M NaCl). Importantly, the binding of osteonectin to type I collagen fibrils was enhanced by limited proteolysis.
Osteotropic agents induce the differential secretion of granulocyte-macrophage colony-stimulating factor by the osteoblast cell line MC3T3-E1
Authors: Dr. Horowitz Mark C. , Coleman David L. , Ryaby James T. , Einhorn Thomas A. 
Published: February 2010

Abstract
Osteoblasts play a central role in the regulation of bone remodeling. Not only are they responsible for the formation of new bone, but they also regulate bone resorption. These cells also exert regulatory influences outside the bone in that they are able to regulate hematopoiesis. However, obtaining pure populations of osteoblasts devoid of contaminating cell types remains problematic. One approach to this problem is the use of cloned osteoblastic cell lines. To this end we have used MC3T3-E1, a cloned murine osteoblast cell line of C57BL/6 origin. We report that MC3T3-E1 cells respond to lipopolysaccharide (LPS) and, to a lesser extent, parathyroid hormone (PTH) by the secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF). However, 1,25-(OH)2D3, a potent activator of osteoblasts, fails to induce these cells to secrete GM-CSF. These results suggest that MC3T3-E1 cells respond to osteotropic agents in a hierarchical fashion. Secretion of GM-CSF is not constitutive but rather requires active induction of the cells. MC3T3 cells fail to secrete detectable levels of interleukin-2 (IL-2), IL-3, or IL-4, regardless of whether or not the cells are activated. The data indicate that MC3T3-E1 cells secrete cytokines in response to osteotropic agents in a way similar to that of normal primary osteoblasts. Therefore, MC3T3-E1 cells may serve as a good in vitro model for primary osteoblasts.
Characterization of a Ca2+-ATPase in osteoclast plasma membrane
Authors: Bekker Petrus J. , Gay Carol V. 
Published: February 2010

Abstract
The plasma membrane fraction of chicken osteoclasts was purified utilizing 20% continuous Percoll gradients. Biochemical marker enzyme analysis (ouabain-sensitive Na+, K+-ATPase and 5′-nucleotidase) indicated that plasma membrane enrichment was 11.87-fold and 7.25-fold, respectively, and contamination with mitochondria, endoplasmic reticulum, and lysosomes was low as determined by succinic dehydrogenase, NADH dehydrogenase, and N-acetylglucosaminidase activities, respectively. SDS latency of Na+K+-ATPase and 5′-nucleotidase activities of the isolated plasma membranes revealed that 43-50% of vesicles were sealed, with 10-16% in the inside-out orientation, depending on the membrane fraction used. Electron microscopy confirmed the vesicular nature of the plasma membrane fraction. The plasma membrane Ca2+-ATPase had a high-affinity (KCa = 0.22 μM; Kmax = 0.16 μmol/mg per min) and a low-affinity (KCa = 148 μM; Vmax = 0.37 μtmol/mg per min) component. Calmodulin (0.12 μM) had no effect on Ca2+-ATPase activity. However, trifluoperazine (0.1 mM), a calmodulin antagonist, strongly inhibited especially the high-affinity component of the enzyme. Vanadate and lanthanum also caused inhibition. In the presence of CDTA, a potent Ca2+ and Mg2+ chelating agent, high-affinity Ca2+-ATPase activity was abolished, indicating that trace Mg2+ was essential for activity. The Ca2+-ATPase substrate curve using ATP showed a high-affinity (Km = 12.3 μM; Kmax= 0.022 μmol/mg per min) and a low-affinity (Km = 43.8 μM; Vmax = 0.278 μmol/mg per min) component. These results demonstrate that osteoclasts have a plasma membrane Ca2+-ATPase with characteristics similar to the enzyme responsible for active calcium extrusion in other cells.
The diltiazem analog TA-3090 mimics the actions of high extracellular Ca2+ on parathyroid function in dispersed bovine parathyroid cells
Authors: Dr. Chen Chu J. , Brown Edward M. 
Published: February 2010

Abstract
We previously showed that the calcium channel blocker diltiazem raises cytosolic Ca2+ and inhibits PTH release in bovine parathyroid cells. To investigate further possible mechanisms underlying these effects, we examined the effects of the more potent diltiazem analog TA-3090, which is a Ca2+ channel antagonist in vascular smooth muscle, on several aspects of the function of dispersed bovine parathyroid cells. Like diltiazem, TA-3090 (10-6-10-4) produced a dose-dependent inhibition of immunoreactive PTH release at 0.5 mM Ca2+ and raised the cytosolic Ca2+ concentration by 25-50% in fura-2-loaded parathyroid cells in the presence but not in the absence of extracellular Ca2, suggesting that it activated rather than inhibited Ca2+ channels. To determine whether this compound affects other aspects of parathyroid function, we examined its effects on the inhibition of cAMP accumulation by Ca2+, a process we recently found to involve inhibition of cAMP generation by G1 through a receptorlike mechanism, which is independent of changes in cytosolic Ca2+, TA-3090 (10−4 M) inhibited dopamine-stimulated cAMP accumulation by up to 75% (from 663 to 166 fmol per 105 cells), with a higher apparent potency at greater extracellular Ca2+ concentrations. Moreover, the addition of 10−4 M TA-3090 potentiated the inhibitory effects of both Ca2+ and Mg2+, decreasing the concentration of the divalent cation necessary to produce half-maximal inhibition of cAMP accumulation by about twofold. In the absence of extracellular Ca2+, however, TA-3090 had no effect on the stimulation of cAMP by dopamine or on the inhibition of dopamine-stimulated cAMP accumulation by PGF2a, which also regulates cAMP via G1. Finally, the effects of TA-3090 on the inhibition of cAMP by Ca2+ were totally abolished following preincubation with pertussis toxin for 20-24 h. These data suggest that TA-3090 not only modulates the function of bovine parathyroid cells at the level of Ca2+ channels per se but also may affect cAMP metabolism by potentiating the effects of high extracellular Ca2+ concentrations at or near the putative Ca2+ “receptor” or “sensor.”
Recombinant murine interferon-γ inhibits the fusion of mouse alveolar macrophages in vitro but stimulates the formation of osteoclastlike cells on implanted syngeneic bone particles in mice in vivo
Authors: Vignery Agnès , Niven-Fairchild Tracy , Shepard Michael H. 
Published: February 2010

Abstract
Osteoclasts are multinucleated cells that originate from the fusion of mononuclear precursors and are responsible for bone resorption. Indirect evidence from in vitro studies suggests that IFN-γ and TNF-α inhibit and stimulate bone resorption, respectively, but contradictory results have emerged from the literature regarding the effects of IFN-γ on macrophage multinucleation. Using highly sensitive model systems, the present work demonstrates that, in mice, rMuIFN-γ inhibits the fusion of alveolar macrophages in vitro but augments the number of osteoclastlike cells on implanted syngeneic bone particles in vivo. Although rMuTNF-α fails to stimulate macrophage multinucleation in either system, treatment of implanted animals with rMuIFN-γ appears to limit the inflammatory reaction and favor tissue repair.
Prostaglandin E2 inhibits formation of osteoclastlike cells in long-term human marrow cultures but is not a mediator of the inhibitory effects of transforming growth factor β
Authors: Chenu C. , Kurihara N. , Mundy G.R. , Roodman G. David 
Published: February 2010

Abstract
Prostaglandins are important local regulators of bone cell function and have been shown to have multiple effects on osteoclasts. Using a human bone marrow culture system in which multinucleated cells with osteoclast characteristics form, we have recently shown that TGF-β is a potent inhibitor of osteoclastlike cell formation and appears to act at several stages of their development. Because it has been suggested that the effects of TGF-β are mediated via a prostaglandin-dependent mechanism, we determined the effects of prostaglandin E2 (PGE2) on total and osteoclastlike cell formation (detected by reactivity with the 23c6 monoclonal antibody, which identifies osteoclasts) in human marrow cultures and tested whether prostaglandin synthesis was responsible for the inhibitory effects of TGF-β on multinucleated cell formation. These studies show that PGE2 is a potent inhibitor of both 23c6-positive and negative multinucleated cell formation in human marrow cultures and that the effects of TGF-β on multinucleated cell formation are not mediated by PGE2.
Mechanisms underlying the stimulation of PTH release by GppNHp in permeabilized bovine parathyroid cells
Authors: Leboff Meryl S. , Oetting Marguerite , Brown Edward M. 
Published: February 2010

Abstract
We examined changes in cAMP and inositol phosphate metabolism to assess the contribution of the guanine nucleotide regulatory (G) protein(s) regulating adenylate cyclase and phospholipase C in mediating the stimulatory effects of GppNHp on PTH release from permeabilized bovine parathyroid cells. To examine the role of Gs, the G protein stimulating adenylate cyclase, and cAMP on PTH release, permeabilized cells were incubated with either GppNHp or isoproterenol, and the effects of these agents on PTH release and cellular cAMP content were determined by RIA. To study the effects of GppNHp on inositol phosphate accumulation, permeabilized cells prelabeled with [3H]inositol were exposed to GppNHp, and inositol phosphates were measured using ion-exchange chromatography. These studies revealed that isoproterenol produced a dose-dependent increment in cAMP content in permeabilized cells with no significant effect on PTH release. Conversely, GppNHp rapidly and markedly elevated PTH release with a smaller and delayed rise in cAMP content. GppNHp- also promoted a dose-dependent increase in inositol monophosphate (IP), inositol bisphosphate (IP2), and inositol trisphosphate (IP3) accumulation, suggesting activation of phosphoinositide hydrolysis. Addition of dioctanoylglycerol, however, a synthetic diacylglycerol (DG) that activates protein kinase C, produced a much smaller increment in PTH release than GppNHp. Moreover, reducing the free calcium concentration to &lt; 10−9 M by adding 10 mM EGTA to the permeabilization medium dissociated the effects of GppNHp and DG on secretion, increasing GppNHp-stimulated PTH release while reducing PTH secretion evoked by DG. In summary, (1) changes in cAMP content cannot account for the effects of GppNHp on PTH release; and (2) GppNHp increases the hydrolysis of phosphoinositides, but the addition of exogenous diacylglycerol does not mimic quantitatively the effects of GppNHp on hormone release. Thus, a G protein may be involved in the control of PTH release in permeabilized cells, perhaps by directly stimulating secretion at a locus distal to the regulation of cAMP or phosphoinositide metabolism.
Effects of parathyroid hormone, calcitonin, and dibutyryl-cyclic AMP on osteoclast area in cultured chick tibia
Authors: Pandalai Sudha , Dr. Gay Carol V. 
Published: February 2010

AbstractSlices of osteoclast-enriched endosteal surfaces of 3 week chick tibia were cultured for 1-3 days. Osteoclasts on the bone surface were made visible by acridine orange fluorescence. Osteoclast area was measured by image analysis. Parathyroid hormone (PTH) caused osteoclasts to increase in area about 40%, and calcitonin (CT) caused a decrease in area also of about 40%. Subsequent addition of dibutyryl cyclic AMP to PTH- or to CT-treated cells resulted in a further change of 40 and 30%, respectively. Application of the cyclic AMP analog alone had no effect. All responses were rapid, occurring in 2-4 minutes.
Osteoclasts isolated from membranous bone in children exhibit nuclear estrogen and progesterone receptors
Authors: Pensler Jay M. , Radosevich James A. , Higbee Russell , Langman Craig B. 
Published: February 2010

Abstract
Osteoclasts were isolated from membranous bone from four children without metabolic bone disease who were undergoing craniotomy for either tumor or trauma. Both freshly isolated osteoclasts and those cultured for 4–7 days exhibited the following characteristics: production of tartrate-resistant acid phosphatase (9.5–14.8 units), contraction in response to application of 100 mg/ml of human calcitonin, and formation of resorption lacunae on devitalized bone wafers. Nuclear estrogen and progesterone receptors were demonstrated by immunohistochemical techniques and quantitated in two of the patients by radioimmunoassay (estrogen receptor RIA, 23.6 and 23.8 cpm/μg protein; progesterone receptor RIA, 36.7 and 74.2 cpm/μg protein). The demonstration of sex steroid hormone receptors in the nucleus of osteoclasts derived from children with normal membranous bone has estabished a potential mechanism whereby direct modulation of bone resorption by the sex steroid estrogen and progesterone may occur.
Bone mineral loss and recovery after 17 weeks of bed rest
Authors: Leblanc Adrian D. , Schneider Victor S. , Evans Harlan J. , Engelbretson David A. , Krebs Jean M. 
Published: February 2010

Abstract
The purpose of this work was to determine the rate and extent of bone loss and recovery from long-term disuse and in particular from disuse after exposure to weightlessness. For this purpose, bed rest is used to simulate the reduced stress and strain on the skeleton. This study reports on the bone loss and recovery after 17 weeks of continuous bed rest and 6 months of reambulation in six normal male volunteers. Bone regions measured were the lumbar spine, hip, tibia, forearm, calcaneus, total body, and segmental regions from the total-body scan. The total body, lumbar spine, femoral neck, trochanter, tibia, and calcaneus demonstrated significant loss, p &lt; 0.05. Expressed as the percentage change from baseline, these were 1.4, 3.9, 3.6, 4.6, 2.2, and 10.4, respectively. Although several areas showed positive slopes during reambulation, only the calcaneus was significant (p &lt; 0.05), with nearly 100% recovery. Segmental analysis of the total-body scans showed significant loss (p &lt; 0.05) in the lumbar spine, total spine, pelvis, trunk, and legs. During reambulation, the majority of the regions demonstrated positive slopes, although only the pelvis and trunk were significant (p &lt; 0.05). Potential redistribution of bone mineral was observed: during bed rest the bone mineral increased in the skull of all subjects. The change in total BMD and calcium from calcium balance were significantly (p &lt; 0.05) correlated, R = 0.88.