bluuebunny/crossref_metadata_2025_split huggingface dataset:
Down-regulation of the receptor for parathyroid hormone (PTH) and PTH-related peptide by PTH in primary fetal rat osteoblasts
Authors: Jongen J. W. J. M. , van Hove E. C. Willemstein , van der Meer J. M. , Bos M. P. , Juppner H. , Segre G. V. , Abou-Samra A. B. , Feyen J. H. M. , Herrmann-Erlee M. P. M. 
Published: February 2010

Abstract
We studied the effects of parathyroid hormone (PTH) on PTH parathyroid hormone related peptide (PTHrP) receptor mRNA level, PTHrP binding, and PTH-stimulated cyclic adenosine monophosphate (cAMP) accumulation in osteoblasts, derived from fetal rat calvariae (ROB). Cells isolated during 10–70 minutes of collagenase treatment were seeded at a density of 25,000 cells/cm2 and cultured for 4 days. These cells show a fast increase in cAMP production after stimulation for 5 minutes with 20 nM bovine parathyroid hormone(1-34) (bPTH(1-34)). When ROB are incubated with bPTH(1-34) (0.04–40 nM) for 24 h, a dose-dependent decrease of the PTH/PTHrP receptor mRNA level, PTHrP binding, and PTH-stimulated cAMP accumulation can be observed. Pretreatment of ROB with a high concentration of bPTH(1-34) (40 nM) leads within 15 minutes to a decrease in PTH-stimulated cAMP accumulation. However, it takes ≥3 h before a significant decrease in PTH/PTHrP receptor mRNA level can be observed. Also a significant decrease in PTHrP binding is observed after only 4 h of incubation with bPTH(1-34). Compared with bPTH(1-34), pretreatment of ROB with bPTH(3-34) (40 and 100 nM) for 24 h causes smaller decreases in PTH-stimulated cAMP accumulation, PTHrP binding, and in the PTH/PTHrP receptor mRNA level. We investigated the possible involvement of the protein kinase A signaling pathway in the regulation of the PTH/PTHrP receptor mRNA expression. Both forskolin and (Bu)2AMP decreased PTHrP binding and PTH/PTHrP mRNA levels. These observations suggest that chronic activation of the PKA signaling pathway may down-regulate PTH/PTHrP receptor expression and thus hormone responsiveness in “normal” osteoblasts. In short, we found that the decrease of the PTH-stimulated cAMP accumulation after long-term pretreatment with bPTH(1-34) is correlated with both PTH/PTHrP receptor mRNA level and PTHrP binding. These data also suggest that the initial desensitization (&lt;30 minutes) of PTH-stimulated cAMP responsiveness by pretreatment with a high concentration of bPTH(1-34) (40 nM) is not dependent on the number of available PTH/PTHrP receptors. The protein kinase A signaling pathway is involved in the regulation of the PTH/PTHrP receptor, but, regarding the effect of bPTH(3-34), other signaling systems are also involved.
Signal transduction by basic fibroblast growth factor in rat osteoblastic py1a cells
Authors: Hurley Marja M. , Marcello Kristina , Abreu Christine , Kessler Michael 
Published: February 2010

Abstract
Basic fibroblast growth factor (bFGF) is a potent mitogen for bone. In this study, we utilized the clonal rat osteoblastic cell line, Py1a, to examine signal transduction by bFGF and to determine the role of mitogen activated protein kinases (MAPK) and induction of c-fos mRNA in the mitogenic response to bFGF. Stimulation of [3H]thymidine incorporation (TDR) into DNA by bFGF was determined in the presence of phorbol myristate acetate of (PMA) to down-regulate the protein kinase C (PKC) pathway, genistein, an inhibitor of tyrosine kinase and H-7, a PKC inhibitor, bFGF 10−8 M and PMA 10−7 M increased TDR by 242 and 245%, respectively. Treatment with bFGF or PMA for 5 or 30 minutes increased tyrosine phosphorylation of multiple proteins, and immunoblotting with MAPK-specific antibody revealed that two of these bands were the 42 and 44 kD isoforms of MAPK. PMA and bFGF induced c-fos mRNA expression at 30 minutes. Genistein at 10 μg/ml blocked the mitogenic effect of bFGF and partially inhibited the mitogenic effect of PMA. Genistein at 100 μg/ml also blocked both bFGF- and PMA-induced increases in c-fos mRNA. A 24 h pretreatment with PMA at 10−7 M inhibited the mitogenic response, tyrosine phosphorylation of MAPK, and induction of c-fos mRNA subsequent to the addition of PMA, but not bFGF. H-7 at 50 μM blocked bFGF-induced mitogenesis and c-fos induction, but did not inhibit bFGF-induced tyrosine phosphorylation of MAPK. In this study, we show that the signaling pathway of bFGF and PMA are similar in that they both induce tyrosine phosphorylation of MAP kinases and activate c-fos. However, the signaling pathways ultimately diverge in that once the PKC pathway is down-regulated by PMA pretreatment or blocked by the PKC inhibitor H-7, tyrosine phosphorylation of MAP kinase, c-fos induction, and the mitogenic effect of PMA is blocked. In contrast, down-regulation of the PKC pathway inhibits c-fos and the mitogenic response to bFGF, but not bFGF's effects on tyrosine phosphorylation of MAP kinase.
Ketoconazole and phorbol myristate acetate regulate osteoclast precursor fusion in primary murine marrow culture
Authors: Fan Xian , Biskobing Diane M. , Bain Steven , Dr. Rubin Janet 
Published: February 2010

Abstract
Osteoclast formation requires both precursor proliferation and then fusion into a multinuclear cell. These processes can be separated in primary murine marrow culture where osteoclastogenesis is stimulated by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Here we investigate the regulation of precursor fusion. Ketoconazole, an agent known to inhibit cell fusion, added during the fusion period (days 5–6), dose-dependently inhibited formation of tartrate-resistant acid phosphatase+ (TRAP+) multinucleated cells (TRAP+MNCs), maximally at 62 ± 4% (n = 10). TRAP+MNCs in cultures exposed to 48 h of ketoconazole (1 μM) during fusion had fewer nuclei compared with control (11.7 ± 0.6 vs. 15.1 ± 0.9). This inhibitory effect was completely reversed 24 h after removal of ketoconazole from culture. Phorbol myristate acetate (PMA) stimulated TRAP+MNC formation when given during the last 12 h of culture (2.3 ± 0.2 fold compared with control). This increased formation was unaffected by the addition of hydroxyurea and accompanied by an increase in nuclei per TRAP+MNC (15.5 ± 0.9 vs. 13.1 ± 0.6). Finally, staurosporine decreased TRAP+MNC formation in the presence or absence of PMA, implying that protein kinase C is involved in fusogenic processes. Regulation of fusion appears to be another mechanism by which bone remodeling can be modulated in vivo.
Dietary (n-3) and (n-6) polyunsaturates and acetylsalicylic acid alter ex vivo PGE2 biosynthesis, tissue IGF-I levels, and bone morphometry in chicks
Authors: Watkins Bruce A. , Shen Chwan-L. , Allen Kenneth G. D. , Seifert Mark F. 
Published: February 2010

Abstract
This study examined the effects of dietary (n-6) and (n-3) polyunsaturated fatty acids (PUFA) and acetylsalicylic acid (ASA) on bone ash content, morphometry, fatty acid composition, ex vivo PGE2 biosynthesis, tissue IGF-I concentration, and serum alkaline phosphatase (ALPase) activity in chicks. Newly hatched chicks were fed a semipurified diet containing soybean oil (S) or menhaden oil + safflower oil (M) at 90 g/kg. At 4 days of age, chicks were divided into four equal treatment groups receiving 0 mg (⊖) or 500 mg (⊕) of ASA/kg of diet: S⊖ASA, M⊖ASA, S⊕ASA, and M⊕ASA. Lipid and ASA treatments did not affect bone length, bone ash, or bone mineral content in chicks. Chicks fed M had increased fractional labeled trabecular surface and tissue level bone formation rates, independent of ASA treatment, compared with those given S. A significant fat × ASA interaction effect was found for trabecular bone volume, thickness, separation, and number. Chicks fed S had higher 20:4(n-6) but lower 20:5(n-3) concentrations in liver and bone compared with those given M. Ex vivo PGE2 biosynthesis was higher in liver homogenates and bone organ cultures of chicks fed S compared with the values for those given M at 17 days. ASA treatment decreased ex vivo PGE2 production in liver homogenates and bone organ cultures of chicks, independent of the dietary lipids. Chicks fed ASA had a lower concentration of IGF-I in tibiotarsal bone compared with those not given ASA at 19 days. Serum ALPase activity was higher in chicks given M compared with those fed S, but the values were reversed with ASA feeding. This study demonstrated that both dietary fat and ASA modulated bone PGE2 biosynthesis, and that (n-3) PUFA and fat × ASA interactions altered bone morphometry.
Normal ranges for vertebral height ratios and prevalence of vertebral fracture in hong kong chinese: A comparison with American caucasians
Authors: Lau E. M. C. , Chan H. H. L. , Woo J. , Lin F. , Black D. , Nevitt M. , Leung P. C. 
Published: February 2010

Abstract
We have established the normal ranges for vertebral height ratios and studied the prevalence of vertebral fracture in 481 Chinese women aged 70–79. Our results were compared with those of an American study with a similar methodology. Lateral spine radiographs centered at T8 and L3 were taken, and the anterior, middle, and posterior vertebral heights of each vertebra from T5 to L4 were measured. The means and standard deviations (SDs) of the anterior to posterior, middle to posterior, and posterior to posterior vertebral height ratios were derived after trimming the extreme values from the distribution. The Chinese had smaller vertebral size than the American Caucasians at all levels. Moreover, the anterior to posterior vertebral height ratios were consistently smaller in the Chinese than in the Americans from T10 onward. The means of other vertebral height ratios in the Chinese were similar to the American Caucasians, but the SDs were greater in the Chinese. The prevalence of vertebral fracture was 29% in the Chinese and 25% in the American Caucasians if a cut-off of 3 SD below the mean for vertebral height ratios was used. We conclude that population-specific means and SD should be used for defining vertebral fracture and that the prevalence of vertebral fracture is similar in Hong Kong Chinese and American Caucasians.
Effect of parathyroid hormone (hPTH[1-34]) infusion on serum 1,25-dihydroxyvitamin D and parathyroid hormone in normal women
Authors: Kinyamu H. Karimi , Gallagher J. Christopher , Petranick Kimberly M. , Ryschon Kay L. 
Published: February 2010

Abstract
Calcium absorption declines with age. Because 1,25-dihydroxyvitamin D (1,25(OH)2D) is the major hormone controlling calcium absorption, changes in vitamin D metabolism may account for the malabsorption of aging. Serum levels of 1,25(OH)2D have been reported to either decrease or remain unchanged with age. To assess the effect of aging on renal production of 1,25(OH)2D, we evaluated the response of renal 25OHD 1α hydroxylase to human parathyroid hormone (hPTH(1-34) stimulation in 119 women ages 25-83 years. In this population, baseline serum 25OHD and 1,25(OH)2D values did not significantly change with age, but serum iPTH (r = 0.44; p &lt; 0.001) and serum creatinine (r = 0.31; p &lt; 0.01) increased with age. However, the stimulatory activity of hPTH(1-34) on the renal production of 1,25(OH)2D declined with age (r3 = -0.36; p &lt; 0.001) and was most apparent after age 75, being 50% less than that of younger women. Besides age, the production of 1,25(OH)2D was found to be dependent on baseline serum iPTH (r = -0.31; p &lt; 0.0001). Administration of hPTH(1-34) led to suppression of endogenous PTH, and suppressibility of endogenous PTH declined with age (r = 0.53; p &lt; 0.0001). The increase in serum PTH and decreased suppressibility of PTH with age could be due to mild secondary hyperparathyroidism. The increase in PTH with age is probably responsible for maintaining normal serum 1,25(OH)2D levels in elderly subjects; however, decreased metabolism of 1,25(OH)2D in the elderly could also maintain normal serum 1,25(OH)2D levels.
Evaluation of signal transduction mechanisms for the mitogenic effects of prostaglandin E2 in normal human bone cells in vitro
Authors: Baylink Timothy M. , Mohan Subburaman , Fitzsimmons Robert J. , Baylink David J. 
Published: February 2010

Abstract
Prostaglandin E2 (PGE2) is one of the most potent stimulators of bone formation in vivo. In these studies, we investigated the mechanism(s) underlying PGE2 effects on human bone formation by evaluating the effects of PGE2 on normal human bone cell (HBC) proliferation in vitro. Cell proliferation of normal HBCs was increased by PGE2 as measured by increased [3H]thymidine incorporation after 18 h and increased cell number after 48 h of treatment. The effect of PGE2 to stimulate cell proliferation was biphasic, with a maximum stimulation between 0.01 and 1.0 nM PGE2 in different experiments. At higher concentrations of PGE2 (0.1 μM), HBC proliferation was inhibited. Signal transduction for PGE2 has been reported to include both protein kinase A (PKA) and protein kinase C (PKC) pathways. In these studies, concentrations of PGE2 which stimulated cell proliferation did not increase cyclic adenosine monophosphate (cAMP) production. However, higher concentrations of PGE2 increased cAMP production (7- to 12-fold at 1-10 μM) and inhibited cell proliferation. Because stimulators of PKC, such as phorbol esters, have been reported to stimulate cell proliferation, the action of PKC inhibitors were tested. Both staurosporine and sangivamysin (PKC inhibitors) totally abrogated the effect of PGE2 to stimulate cell proliferation. Additional studies revealed that PGE2 increased 45Ca uptake in a dose-dependent manner with a peak response occuring between 1 and 10 nM PGE2 concentrations in different experiments. Furthermore, when the calcium channel blocker, verapamil, was added to HBC cultures treated with PGE2, the stimulation of 45Ca uptake and cell proliferation by PGE2 was completely blocked. These data suggest that PGE2 increases cell proliferation through activation of a verapamil-sensitive calcium channel. In conclusion, these data are consistent with a model in which stimulation of HBC proliferation by low doses of PGE2 is mediated by an enhancement of phospholipase C, which results in both an increase in PKC activity and an increase in intracellular calcium influx.
Possible involvement of RGD (arg-gly-asp)-containing extracellular matrix proteins in rat growth plate chondrocyte differentiation in culture
Authors: Yasuda Tadashi , Shimizu Katsuji , Nakagawa Yasuaki , Ishikawa Hiroshi , Nishihara Hideki , Nakamura Takashi 
Published: February 2010

Abstract
RGD (arg-gly-asp)-containing proteins have been shown to be components of cartilage matrix. In the present study, the role of interactions of cells with RGD-containing cartilage matrix proteins in rat costal epiphyseal chondrocyte differentiation was examined using a pelleted culture system as an in vitro model of endochondral ossification. Cell attachment assays showed the presence of integrins which mediated the binding of chondrocytes to fibronectin, a member of RGD-containing cartilage matrix proteins, in an RGD-dependent manner. In the early culture period, when chondrocytes had nonhypertrophic morphology with low levels of alkaline phosphatase, the exogenous addition of synthetic peptide GRGDSP (gly-arg-gly-asp-ser-pro) caused an increase in alkaline phosphatase levels and enlargement of chondrocytes in pelleted cultures. Treatment with GRGDSP from the early to late culture periods in association with the transition of chondrocytes from prehypertrophic to hypertrophic phenotypes followed by matrix mineralization resulted in suppression of mineral growth without significant effects on alkaline phosphatase levels or cellular morphology in the cultures. Similarly, addition of the synthetic peptide during the late culture period with the advance of cartilage mineralization suppressed mineral growth in pelleted cultures. These data indicate an important role of interactions of chondrocytes with RGD-containing cartilage matrix proteins through integrins in the regulation of epiphyseal chondrocyte differentiation in pelleted cultures.
Tartrate-resistant acid phosphatase from human bone: Purification and development of an immunoassay
Authors: Halleen Jussi , Hentunen Teuvo A. , Hellman Jukka , Väänlänen H. Kalervo 
Published: February 2010

Abstract
Tartrate-resistant acid phosphatase (TRAP) was purified 20,000-fold to apparent homogeneity from human bone. The purified enzyme consisted of one 32 kd subunit, which was cleaved by β-mercaptoethanol into two subunits of 15 kd and 20 kd, as shown by sodium dodecyl sulfide-polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining. The purified enzyme was identified by N-terminal amino acid sequencing, and it was shown to be homologous with previously purified TRAPs from other sources. We developed a polyclonal antiserum against the purified enzyme in mice. In immunohistochemistry, the antiserum recognized osteoclasts from human bone and alveolar macrophages from human lung tissue, but no cells from human spleen tissue. It also stained osteoclasts from rat bone cells cultured on bovine bone slices. Purified TRAP could be inhibited by vanadate and molybdate, but not by tartrate, and it was activated 2-fold by β-mercaptoethanol. The glycoprotein structure of human bone TRAP was analyzed, and it was shown to contain only high-mannose type carbohydrates. We used the polyclonal antibody to develop a competitive fluorescence immunoassay for measuring serum TRAP concentrations. According to the assay, children have higher serum TRAP concentrations than adults, and postmenopausal women have higher concentrations than premenopausal women. Postmenopausal women also have higher serum TRAP concentrations than postmenopausal women on estrogen replacement therapy.
Evidence for an interaction between calcium intake and physical activity on changes in bone mineral density
Authors: Specker Bonny L. 
Published: February 2010

Abstract
Results of trials on the effects of physical activity on bone mineral density (BMD) are conflicting. The current hypothesis was that calcium intake modifies the bone response to physical activity. Published trials on physical activity and bone density were reviewed, and the results of 17 trials are summarized. Physical activity has beneficial effects on BMD at high calcium intakes, with no effect at mean calcium intakes less than a mean of 1000 mg/day. The modifying effect of calcium intake on BMD among exercise groups is more pronounced in the lumbar spine than in the radius. This analysis may explain conflicting results of trials on physical activity and calcium effects on bone. Controlled trials designed to test adequately this hypothesis are needed.
Purification and characterization of fully functional human osteoclast precursors
Authors: James Ian E. , Dodds Robert A. , Lee-Rykaczewski Elizabeth , Eichman Christopher F. , Connor Janice R. , Hart Timothy K. , Maleeff Beverly E. , Lackman Richard D. , Gowen Maxine 
Published: February 2010

Abstract
The identification and purification of human osteoclast precursors is essential to further our understanding of the mechanisms that control human osteoclast differentiation. Osteoclastoma tissue potentially provides a rich source of human osteoclast precursors, and in previous studies we have demonstrated the existence of a population of mononuclear cells within this tissue that is reactive with osteoclast-selective vitronectin receptor monoclonal antibodies. In this study, mononuclear cells expressing the vitronectin receptor, as defined by their ability to react with a murine monoclonal antibody to the β3 chain of the vitronectin receptor (87MEM1), were isolated from collagenase digests of osteoclastoma tissue using a fluorescence activated cell sorter. Based on their fluorescence signal and size, approximately 2–3% of the viable cells (typically 2 × 105) were obtained and prepared for further phenotyping. The isolated cells demonstrated a number of phenotypic characteristics of osteoclasts: positive tartrate-resistant acid phosphatase (TRAP) activity, reactivity with human osteoclast-selective antibodies, expression of calcitonin receptors, cathepsin K (a novel osteoclast-selective cysteine proteinase) mRNA, and osteopontin mRNA and protein. These phenotypic characteristics were also detected in mononuclear cells within cryostat sections of the native osteoclastoma tissue as well as in resorption lacunae of sections of human bone. In contrast, isolated peripheral blood monocytes were negative for TRAP activity and osteopontin expression and, unlike the osteoclastoma-derived cells, demonstrated strong nonspecific esterase activity. Significantly, when the osteoclastoma-derived 87MEM1 positive cells were cocultured on whale dentine for 1–3 weeks with stromal cells, extensive resorption of the dentine surface was observed. This is the first demonstration of the purification of human osteoclast precursors. These cells provide an homogeneous cell population for studying cellular events that occur during human osteoclast differentiation. (J Bone Miner Res 1996;11:1608-1618)
Leukotriene B4 stimulates osteoclastic bone resorption both in vitro and in vivo
Authors: Garcia Carlos , Boyce Brendan F. , Gilles James , Dallas Mark , Qiao Mei , Mundy Gregory R. , Bonewald Lynda F. 
Published: February 2010

AbstractUpon activation, the enzyme 5‐lipoxygenase converts arachidonic acid into principally three products, the peptido‐leukotrienes, 5‐hydroperoxyeicosatetraenoic acid (5‐HETE) or the leukotriene B4. We have shown that the peptido‐leukotrienes (known as LTC4, LTD4, or LTE4) and 5‐HETE induce osteoclastic bone resorption and that receptors for LTD4 are present on isolated avian osteoclast‐like cells. Here, we show the effects of the third metabolic product of the 5‐lipoxygenase (5‐LO) pathway of arachidonic acid metabolism, the leukotriene LTB4, on osteoclastic bone resorption both in vivo and in vitro. Because LTB4 production is increased in a number of inflammatory conditions, it may be an important contributor to the bone loss which occurs in these disorders. LTB4 increased osteoclastic bone resorption in vivo following local administration over the calvariae of normal mice and in vitro in organ cultures of neonatal mouse calvariae. When LTB4 was injected over the calvaria of mice, there was a significant increase in bone resorption, osteoclast numbers, and eroded surfaces. LTB4 also increased the formation of resorption lacunae by isolated neonatal rat osteoclasts. Greater potency was observed with LTB4 compared with the peptido‐leukotriene LTD4. This is in contrast to prostaglandins of the E series, which are reported to inhibit isolated osteoclasts. Experiments using marrow cultures suggest that LTB4 stimulates bone resorption in part by enhancing the formation of osteoclasts. (J Bone Miner Res 1996;11:1619‐1627)