bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seasonal Deficiency of Vitamin D in Children: A Potential Target for Osteoporosis-Preventing Strategies?
Authors: Docio Suceso , Riancho José A. , Pérez Amabilia , Olmos José M. , Amado José A. , González-Macías Jesús 
Published: April 2006

Abstract
Peak bone mass attained after skeletal growth is a major determinant of the risk of developing osteoporosis later in life, hence the importance of nutritional factors that contribute to bone mass gain during infancy and adolescence. An adequate supply of vitamin D is essential for normal bone homeostasis. This study was undertaken to determine what the levels are of 25-hydroxyvitamin D (25(OH)D) that may be considered desirable in children and to assess if normal children maintain these levels throughout the year. Vitamin D metabolites and parathyroid hormone (PTH) serum levels were measured in 21 children in March and October, prior to and after the administration of a daily supplement of 25(OH)D (40 μg for 7 consecutive days). There were inverse correlations between basal 25(OH)D levels and supplementation-induced changes in serum 1,25(OH)2D (r = 0.57, p &lt; 0.05) and PTH (r = 0.41, p &lt; 0.05). When basal levels of 25(OH)D were below 20 ng/ml, the supplement induced an increase in serum 1,25(OH)2D; with basal 25(OH)D under 10–12 ng/ml, the supplement also decreased serum PTH. The lowest serum level of 25(OH)D in 43 normal children studied in summer was 13 ng/ml. Those results suggested that the lowest limit for desirable levels of 25(OH)D in children was somewhere between 12 and 20 ng/ml. However, 31% of 51 normal children studied in winter had levels below 12 ng/ml, and 80% had levels lower than 20 ng/ml. Those children are likely to have suboptimal bioavailability of vitamin D, which might hamper their achievement of an adequate peak bone mass. Since cutaneous synthesis of vitamin D is rather limited in winter, oral vitamin D supplementation should be considered.
The Biological Activity of Nonsteroidal Vitamin D Hormone Analogs Lacking Both the C- and D-Rings
Authors: Verstuyf Annemieke , Verlinden Lieve , Van Baelen Hugo , Sabbe Katrien , D'Hallewyn Chris , De Clercq Pierre , Vandewalle Maurits , Bouillon Roger 
Published: April 2006

Abstract
1α,25-dihydroxyvitamin D is a key calcium-regulating hormone but also displays potent differentiating and antiproliferative activities on many cell types. The structural requirements of this secosteroid hormone have been extensively studied for the A-ring and side chain, whereas relatively little is known about the requirements of the natural CD-ring structure for the vitamin D–like biological activity. We have embarked on a vast program in which derivatives were synthesized and evaluated characterized by profound structural changes in the central C/D-region. This first series of nonsteroidal analogs consists of (1R,3S)-5-((Z,2E)-4-((1S,3S)-3-(4-hydroxy-4-methylpentyl)-1,2,2,-trimethylcyclopentyl)-2-butenylidene)-4-methylenecyclohexane-1,3-diol (KS 176) and derivatives thereof. These analogs are characterized by the absence of normal C- and D-rings and by the presence of an unnatural five-membered ring which we call the E-ring. KS 176 with the otherwise natural side chain structure of 1α,25(OH)2D3 has between 10 and 30% of the biological activity of 1α,25(OH)2D3 when tested in vitro (prodifferentiating effects on HL-60 and MG-63; antiproliferating activity on MCF-7 and keratinocytes) but has minimal in vivo calcemic effects. Introduction of several side chain modifications created analogs with increased intrinsic noncalcemic biological properties, whereas their calcemic potency remains very low. These data demonstrate that the full CD-rings are not mandatory for the biological activity of 1α,25(OH)2D3 since they can be replaced by a new ring structure which generates an appropriate spacing of the A-seco B-rings in relation to the side chain. The biological activity of these nonsteroidal analogs probably involves a classical genomic activation since they are also active in transfection assays using an osteocalcin vitamin D responsive element coupled to a human growth hormone reporter gene.
Na+-Phosphate Cotransport in Mouse Distal Convoluted Tubule Cells: Evidence for Glvr-1 and Ram-1 Gene Expression
Authors: Tenenhouse Harriet S. , Gauthier Claude , Martel Josée , Gesek Frank A. , Coutermarsh Bonita A. , Friedman Peter A. 
Published: April 2006

Abstract
While there is considerable evidence for phosphate (Pi) reabsorption in the distal tubule, Pi transport and its regulation have not been well characterized in this segment of the nephron. In the present study, we examined Na+-dependent Pi transport in immortalized mouse distal convoluted tubule (MDCT) cells. Pi uptake by MDCT cells is Na+-dependent and, under initial rate conditions, is inhibited by phosphonoformic acid (41 ± 3% of control), a competitive inhibitor of Na+-Pi cotransport. The transport system has a high affinity for Pi (Km = 0.46 mM) and is stimulated by lowering the extracellular pH from 7.4 to 6.4 and inhibited by raising the pH from 7.4 to 8.4. Exposure to Pi-free medium for 21 h increased Na+-Pi cotransport from 2.1 to 5.5 nmol/mg of protein/5 minutes (p &lt; 0.05) while parathyroid hormone, forskolin, and phorbol 12-myristate 13-acetate failed to alter Pi uptake in MDCT cells. Reverse transcriptase polymerase chain reaction of MDCT cell RNA provided evidence for the expression of the Npt1 but not the Npt2 Na+-Pi cotransporter gene. However, preincubation of MDCT cells with Npt1 antisense oligonucleotide led to only 20% inhibition of Na+-Pi cotransport, suggesting that other Na+-Pi cotransporters are operative in MDCT cells. Indeed, we showed, by ribonuclease protection assay, that MDCT cells express the ubiquitous cell surface receptors for gibbon ape leukemia virus (Glvr-1) and amphoteric murine retrovirus (Ram-1) that also function as Na+-Pi cotransporters. In summary, we demonstrate that the pH dependence and regulation of Na+-Pi cotransport in MDCT cells is distinct from that in the proximal tubule and suggest that different gene products mediate Na+-Pi cotransport in the proximal and distal segments of the nephron.
Immortalization and Characterization of Bone Marrow Stromal Fibroblasts from a Patient with a Loss of Function Mutation in the Estrogen Receptor-α Gene
Authors: Dieudonné S. C. , Xu T. , Chou J. Y. , Kuznetsov S. A. , Satomura K. , Mankani M. , Fedarko N. S. , Smith E. P. , Robey P. Gehron , Young M. F. 
Published: April 2006

Abstract
A male patient with abnormal postpubertal bone elongation was shown earlier to have a mutation in both alleles of the estrogen receptor, resulting in a nonfunctional gene. Marrow stromal fibroblasts (MSFs) derived from this patient were called HERKOs (human estrogen receptor knock outs), and in order to obtain continuous HERKO cell lines, they were immortalized using a recombinant adenovirus-origin-minus SV40 virus. MSFs are unique cells because they support hematopoesis and contain a mixed population of precursor cells for bone, cartilage, and fat. Three established cell lines (HERKO2, HERKO4, and HERKO7) were characterized and compared with the heterogeneous population of nonimmortalized HERKOs for their osteogenic potential. We performed Northern analysis of matrix genes implicated in bone development and metabolism and an in vivo bone formation assay by transplanting the cells subcutaneously into immunodeficient mice. All three HERKO lines expressed high amounts of collagen 1A1, osteopontin, osteonectin, fibronectin, decorin, biglycan, and alkaline phosphatase. Except for osteopontin, expression of these genes was slightly lower compared with nonimmortalized HERKOs. In the in vivo bone formation assay, the heterogeneous population of nonimmortalized HERKOs formed bone with high efficiency, while the HERKO lines induced a high-density, bone-like matrix. Finally, all HERKO cell types secreted high levels of insulin-like growth factor I and interleukin-6 into the culture medium relative to cells of normal human subjects. In summary, these lines of HERKO cells retain several of the phenotypic traits of MSFs after immortalization, including matrix and cytokine production, and provide a valuable source of a unique human material for future studies involving estrogen action in bone and bone marrow metabolism.
Reciprocal Temporospatial Patterns of Msx2 and Osteocalcin Gene Expression During Murine Odontogenesis
Authors: Bidder Miri , Latifi Tammy , Dr. Towler Dwight A. 
Published: April 2006

Abstract
Msx2 is a homeodomain transcription factor that regulates craniofacial development in vivo and osteocalcin (Osc) promoter activity in vitro. Msx2 is expressed in many craniofacial structures prior to embryonic day (E) E14 but is expressed at later stages in a restricted pattern, primarily in developing teeth and the calvarium. We examine Osc expression by in situ hybridization during murine development, detailing temporospatial relationships with Msx2 expression during preappositional and appositional odontogenesis and calvarial osteogenesis. Osc expression at E14–14.5 is very low, limited to a few perichondrial osteoblasts in the dorsal aspect of developing ribs. At E16.5 and E18.5, Osc expression is much higher, widely expressed in skeletal osteoblasts, including calvarial osteoblasts that do not express Msx2. No Osc is detected in early preappositional teeth that express Msx2. In incisors studied at an early appositional phase, Msx2 is widely expressed in the tooth, primarily in ovoid preodontoblasts and subjacent dental papilla cells. Osc is detected only in a small number of maturing odontoblasts that also express α1(I) collagen(Col1a1) and that are postproliferative (do not express histone H4). Msx2 expression greatly overlaps both histone H4 and Col1a1 expression in ovoid preodontoblasts and dental papilla cells. By the late appositional phases of E18.5 and neonatal teeth, Osc mRNA is highly expressed in mature columnar odontoblasts adjacent to accumulating dentin. In appositional bell-stage molars, reciprocal patterns of Msx2 and Osc are observed in adjacent preodontoblasts and odontoblasts within the same tooth. Osc is expressed in mature columnar odontoblasts, while Msx2 is expressed in adjacent immature ovoid preodontoblasts. In less mature teeth populated only by immature ovoid preodontoblasts, only Msx2 is expressed-–no Osc is detected. Thus, Msx2 and Osc are expressed in reciprocal patterns during craniofacial development in vivo, and Msx2 expression in preodontoblasts clearly preceeds Osc expression in odontoblasts. In functional studies using MC3T3-E1 calvarial osteoblasts, Msx2 suppresses endogeneous Osc, but not osteopontin, mRNA accumulation. In toto, these data suggest that Msx2 suppresses Osc expression in the craniofacial skeleton at stages immediately preceeding odontoblast and osteoblast terminal differentiation.
Spatiotemporal Assessment of Fetal Bovine Osteoblast Culture Differentiation Indicates a Role for BSP in Promoting Differentiation
Authors: Cooper L. F. , Yliheikkilä P. K. , Felton D. A. , Whitson S. W. 
Published: April 2006

Abstract
Fetal bovine mandible-derived osteoblasts were cultured for the purpose of obtaining a spatiotemporal assessment of bone matrix protein expression during in vitro differentiation. The results obtained from electron microscopic, immunohistological, biochemical, and molecular biological analyses indicated that these primary cultured osteoblasts produce an abundant extracellular matrix which mineralizes during a 14-day culture period. During this process, a restricted, spatiotemporal pattern of bone sialoprotein expression was indicated by immunohistological and molecular evaluations. To test the possibility that bone sialoprotein promoted the continued morphodifferentiation of osteoblastic cells, cultures were grown in the presence of anti-bone sialoprotein antibodies known to interfere with cell–bone sialoprotein attachment. Compared with cultures grown in the presence of normal rabbit serum (1:150), cultures grown in the media containing anti-bone sialoprotein antibody (1:150) failed to mineralize as demonstrated by von Kossa staining and failed to express osteocalcin and osteopontin as shown by the reverse transcription polymerase chain reaction. These results contribute to the growing evidence that bone sialoprotein is an important determinant of osteoblast differentiation and bone formation. Matrix protein–cell interactions may be examined using this spatiotemporally defined model.
Human Osteoblasts Express a Repertoire of Cadherins, Which Are Critical for BMP-2–Induced Osteogenic Differentiation
Authors: Cheng Su-Li , Lecanda Fernando , Davidson Mari K. , Warlow Pamela M. , Zhang Shu-Fang , Zhang Liming , Suzuki Shintaro , St. John Tom , Civitelli Roberto 
Published: April 2006

Abstract
Direct cell–cell interactions are fundamental for tissue development and differentiation. We have studied the expression and function of cadherins in human osteoblasts during in vitro differentiation. Using reverse transcription-polymerase chain reaction and mRNA hybridization, we found that human trabecular bone osteoblasts (HOBs), osteoprogenitor marrow stromal cells (BMCs), and the osteogenic sarcoma lines, SaOS-2 and MG-63, expressed mRNA for cadherin-11 (C11) and N-cadherin (N-cad). HOBs and BMCs also expressed low levels of cadherin-4 (C4) mRNA. C11 was the most abundant cadherin protein present in human osteoblasts, and its expression was unaffected by bone morphogenetic protein-2 (BMP-2) treatment of either BMCs or HOBs. Likewise, N-cad mRNA did not change during BMP-2 incubation. Conversely, C4 protein, undetectable in transformed cell lines, was down-regulated by BMP-2 treatment of normal cells. Both C11 and C4 were localized to sites of cell–cell contact in both HOBs and BMCs, colocalized with β-catenin, and bands corresponding to cadherins were coimmunoprecipitated by a β-catenin antibody, findings indicative of functional cadherins. A decapeptide containing the HAV motif of human N-cad partially inhibited Ca2+-dependent cell–cell adhesion and completely prevented BMP-2–induced stimulation of alkaline phosphatase activity by BMCs. Thus, human osteoblasts and their progenitor cells express a repertoire of multiple cadherins. Cadherin-mediated cell-to-cell adhesion is critical for normal human osteoblast differentiation.
The Effects of Fibroblast Growth Factor-2 on Human Neonatal Calvaria Osteoblastic Cells Are Differentiation Stage Specific
Authors: Debiais F. , Hott M. , Graulet A. M. , Marie P. J. 
Published: April 2006

Abstract
Fibroblast growth factors (FGFs) appear to play an important role in human cranial osteogenesis. We therefore investigated the effects of recombinant human FGF-2 (rhFGF-2) on human calvaria (HC) osteoblastic cells. Immunocytochemical analysis showed that confluent HC cells express both FGF receptors -1 and -2. In short-term culture, rhFGF-2 (0.1–100 ng/ml, 2–5 days) increased HC cell growth and decreased alkaline phosphatase (ALP) activity and type I collagen (ColI) synthesis, as evaluated by P1CP levels. When HC cells were induced to differentiate in long-term culture in the presence of 50 μg/ml ascorbic acid and 3 mM phosphate, HC cells initially proliferated, then ALP activity and ColI synthesis decreased and calcium content in the extracellular matrix increased. Continuous treatment with rhFGF-2 (50 ng/ml) for 1–28 days, or a transient rhFGF-2 treatment for 1–7 days, slightly increased DNA synthesis at 7 days, whereas a late treatment for 8–28 days had no effect on cell growth. The continuous and transient treatments with rhFGF-2 decreased ALP activity, ColI synthesis, and matrix mineralization. This was associated with a transient fall in osteocalcin (OC) production at 7 days. In contrast, the late rhFGF-2 treatment for 8–28 days only slightly inhibited ALP activity and increased matrix mineralization. In addition, both continuous and late treatments with rhFGF-2 increased OC production in more mature cells at 3–4 weeks of culture. We also found that the early and late treatments with rhFGF-2 had opposite effects on transforming growth factor β2 production in proliferating cells and more mature cells. The results show that rhFGF-2 slightly stimulates cell growth and reduces the expression of osteoblast markers in less mature cells, whereas it induces OC production and matrix mineralization in more mature cells, indicating that the effects of FGF-2 are differentiation stage specific and that FGF-2 may modulate HC osteogenesis by acting at distinct stages of cell maturation.
Concentration of Transforming Growth Factor Beta in Human Bone Tissue: Relationship to Age, Menopause, Bone Turnover, and Bone Volume
Authors: Pfeilschifter Johannes , Diel Ingo , Scheppach Beate , Bretz Anette , Krempien Robert , Erdmann Johannes , Schmid Gerald , Reske Nicole , Bismar Hanadi , Seck Thomas , Krempien Burkhard , Ziegler Reinhard 
Published: April 2006

Abstract
Transforming growth factor β (TGF-β) is thought to play an important role in bone metabolism, but its relationship to human bone turnover and bone mass has not been examined yet. In this study, we measured the concentration of TGF-β in 811 samples of male and female bone from four representative sites of the human skeleton and in the supernatants of 72 short-term human bone marrow cultures from the iliac crest. The concentrations of TGF-β1 and TGF-β2 in the bone matrix were positively correlated with histomorphometric indices of bone resorption and bone formation and with serum levels of osteocalcin and bone-specific alkaline phosphatase. We also observed a positive association between the release of TGF-β in the bone marrow cultures and serum osteocalcin. Changes in the rate of cancellous or cortical bone remodeling with age or menopause were accompanied by corresponding changes in skeletal TGF-β. In contrast, there was no significant relationship between the concentration of TGF-β and bone volume at any skeletal site. In conclusion, our study supports the hypothesis that TGF-β plays an important role in human bone remodeling, but fails to demonstrate an association between the skeletal concentration of TGF-β and human bone mass.
Human Growth Hormone Locally Released in Bone Sites by Calcium-Phosphate Biomaterial Stimulates Ceramic Bone Substitution Without Systemic Effects: A Rabbit Study
Authors: Guicheux Jérôme , Gauthier Olivier , Aguado Eric , Pilet Paul , Couillaud Séverine , Jegou Dominique , Daculsi Guy , Heymann Dominique 
Published: April 2006

Abstract
Calcium-phosphate bone replacement biomaterial has been used as a drug carrier for therapeutic agents. This study investigated the efficacy of local administration of human growth hormone (hGH) by macroporous biphasic calcium phosphate (MBCP) implants in improving the bone substitution qualities of ceramics. hGH release from MBCP implants loaded with 1 μg of hGH was rapid during the first 48 h and then sustained for a total of 9 days. Immunolocalization of hGH in vitro and in vivo by transmission electron microscopy showed its presence inside the material, indicating that it was able to penetrate within the porosity of the ceramic during the adsorption process. MBCP cylinders (6 × 6 mm) were loaded with 0.1, 1, and 10 μg of hGH and implanted into rabbit femurs (n = 40). The effects of locally released hGH on bone ingrowth and ceramic resorption were evaluated by scanning electron microscopy and image analysis. The results indicated that hGH increased bone ingrowth (+65%) and ceramic resorption (+140%) significantly in comparison with control implants and that the increase was dose dependent. Biochemical parameters monitored in rabbit plasma and urine, as well as the absence of any significant difference between contralateral implants and the control, indicated that hGH did not produce detectable systemic effects. Thus, the use of MBCP appears to be effective for local delivery of hGH, resulting in improved bone substitution.
A Unitary Model for Involutional Osteoporosis: Estrogen Deficiency Causes Both Type I and Type II Osteoporosis in Postmenopausal Women and Contributes to Bone Loss in Aging Men
Authors: Riggs B. Lawrence , Khosla Sundeep , Melton L. Joseph 
Published: April 2006

Abstract
We propose here a new unitary model for the pathophysiology of involutional osteoporosis that identifies estrogen (E) deficiency as the cause of both the early, accelerated and the late, slow phases of bone loss in postmenopausal women and as a contributing cause of the continuous phase of bone loss in aging men. The accelerated phase in women is most apparent during the first decade after menopause, involves disproportionate loss of cancellous bone, and is mediated mainly by loss of the direct restraining effects of E on bone cell function. The ensuing slow phase continues throughout life in women, involves proportionate losses of cancellous and cortical bone, and is associated with progressive secondary hyperparathyroidism. This phase is mediated mainly by loss of E action on extraskeletal calcium homeostasis which results in net calcium wasting and increases in the level of dietary calcium intake required to maintain bone balance. Because elderly men have low circulating levels of both bioavailable E and bioavailable testosterone (T) and because recent data suggest that E is at least as important as T in determining bone mass in aging men, E deficiency may also contribute substantially to the continuous bone loss of aging men. In both genders, E deficiency increases bone resorption and may also impair a compensatory increase in bone formation. For the most part, this unitary model is well supported by observational and experimental data and provides plausible explanations to traditional objections to a unitary hypothesis.
Combination of Interleukin-6 and Soluble Interleukin-6 Receptors Induces Differentiation and Activation of JAK-STAT and MAP Kinase Pathways in MG-63 Human Osteoblastic Cells
Authors: Nishimura Riko , Moriyama Keiji , Yasukawa Kiyoshi , Mundy Gregory R. , Yoneda Toshiyuki 
Published: April 2006

Abstract
Studies on the role of interleukin-6 (IL-6) in bone metabolism have been accumulating. However, its effects on osteoblasts are still unclear because the results are conflicting depending on the study models employed. We reasoned that these conflicting data are due to variable expression levels of membrane-bound IL-6 receptors (IL-6Rs). In the present study, we found that IL-6 in combination with soluble IL-6R (sIL-6R) consistently caused a marked elevation of alkaline phosphatase and a decrease in proliferation in the human osteoblastic cell line MG-63, which expressed no detectable membrane-bound IL-6R and failed to respond to IL-6. These effects of IL-6/sIL-6R were blocked by neutralizing antibodies to the IL-6 signal transducer gp130, suggesting an involvement of IL-6 signaling in the elicitation of the effects of IL-6/sIL-6R. Upon stimulation with IL-6/sIL-6R, the gp130, cytoplasmic Janus kinases JAK1 and JAK2 were tyrosine phosphorylated. Moreover, signal transducers and activators of transcription STAT1 and STAT3 were also tyrosine phosphorylated, translocated to the nucleus, and bound to the putative STAT-binding DNA elements. In addition, mitogen-activated protein (MAP) kinase was also activated in response to IL-6/sIL-6R. These data demonstrate that sIL-6R may enhance the responsiveness of MG-63 cells to IL-6. Thus, IL-6 in collaboration with sIL-6R may modulate differentiation and proliferation of osteoblastic cells, presumably by activating two distinct signaling pathways of JAK-STAT and MAP kinase.