Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.3.1 (alkaline phosphatase)
 47,916 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Osteoprogenitor cells present in human fetal bone marrow (BM) stroma have not been characterized. We used density gradient centrifugation, aggregation on binding lectin, and enrichment by magnetic activated cell sorting with STRO-1 antibody to isolate STRO-1+ cells from nonadherent human fetal BM stromal cells. Immunoselected STRO-1+ cells were immortalized using SV-40 large T antigen and a clone, F/STRO-1+ A, with weak alkaline phosphatase (ALP) activity was selected. The cloned cells proliferated rapidly but were not tumorigenic. Preconfluent F/STRO-1+ A cells showed immunoreactivity for osteopontin, alpha1(I) procollagen, and parathyroid hormone-related peptide, but not for the late osteoblast differentiation markers, osteocalcin (OC), or bone sialoprotein. However, differentiation of F/STRO-1+ A cells was induced by dexamethasone and 1,25-dihydroxyvitamin D3, as shown by increased ALP activity. In addition, osteogenesis occurred in F/STRO-1+ A cells cultured in three-dimentional aggregates, as assessed morphologically, histologically, and biochemically. Moreover, reverse transcription-polymerase chain reaction analysis showed that OC expression was silent in exponentially growing cells and occurred when cell-cell contacts were established in monolayer and in aggregates, showing induction of mature osteoblast phenotype by cell-cell contacts. Thus, clonal F/STRO-1+ A cells immunoselected from human fetal BM stroma display features of immature osteoprogenitor cells which can differentiate into mature osteogenic cells by cell-cell interactions or inducing agents. The generation by immunoselection of an immortalized clonogenic human fetal BM stroma-derived cell line which behaves like an osteoprogenitor cell provides a novel model system for identifying the signals required for the commitment of osteoprogenitors in the human fetal BM stroma.
 ...
PMID:Isolation and characterization of human clonogenic osteoblast progenitors immunoselected from fetal bone marrow stroma using STRO-1 monoclonal antibody. 1002

An in vitro mineralizing cell-implant system was developed to study osteoblast attachment, secretion of extracellular (ECM) matrix proteins and mineralization. Saos-2 cells were plated on Tivanium (Tiv, Ti-6A1-4V), Zimaloy (Zim, Co-Cr-Mo) and glass disks. The cells were cultured in alpha-MEM medium with 10% fetal bovine serum and 50 microg ml(-1) ascorbic acid. The cultures were analyzed for calcification and for mRNA expression for ECM proteins after 1, 2, 4 and 6 weeks. Calcium content was significantly higher in cells on Tiv, less on Zim and least on glass disks. With the addition of 3 mm beta-glycerophosphate (beta-GP), the cell layer was more calcified on Zim than on Tiv and all substrates had three times more calcium than cultures without beta-GP. All subsequent experiments were performed without beta-GP. Phalloidin immunofluorescence microscopy of the actin-based cytoskeleton at 2 weeks demonstrated nodules composed of multilayered, cobblestone-appearing osteoblasts overlying calcified matrix which was stained with calcein. On Tiv, calcified nodules were connected in a trabecular-like pattern while on Zim, calcification was dispersed throughout the cell layer. Northern blots for alkaline phosphatase, bone sialoprotein, osteocalcin and alpha1(I) procollagen mRNAs were performed at different time points. The amount and pattern of calcification as well as the expression of ECM-mRNAs differed on each implant material. The results indicate that Tiv stimulates the production of more ECM proteins and mineralized matrix than Zim or glass in this osteoblast-like cell/implant culture.
 ...
PMID:An in vitro model for mineralization of human osteoblast-like cells on implant materials. 1003 May 97

Cells of the bone marrow stroma can reversibly convert among different phenotypes. Based on this and on evidence for a reciprocal relationship between osteoblastogenesis and adipogenesis, we have isolated several murine bone marrow-derived clonal cell lines with phenotypic characteristics of osteoblasts or adipocytes, or both. Consistent with a state of plasticity, cell lines with a mixed phenotype synthesized osteoblast markers like type I collagen, alkaline phosphatase, osteocalcin, as well as the adipocyte marker lipoprotein lipase, under basal conditions. In the presence of ascorbic acid and beta-glycerophosphate-agents that promote osteoblast differentiation-they formed a mineralized matrix. In the presence of isobutylmethylxanthine, hydrocortisone, and indomethacin-agents that promote adipocyte differentiation-they accumulated fat droplets, but failed to express adipsin and aP2, markers of terminally differentiated adipocytes. Furthermore, they were converted back to matrix mineralizing cells when the adipogenic stimuli were replaced with the osteoblastogenic ones. A prototypic cell line with mixed phenotype (UAMS-33) expressed Osf2/Cbfa1-a transcription factor required for osteoblast differentiation, but not PPARgamma2-a transcription factor required for terminal adipocyte differentiation. Stable transfection with a PPARgamma2 expression construct and activation with the thiazolidinedione BRL49653 stimulated aP2 and adipsin synthesis and fat accumulation, and simultaneously suppressed Osf2/Cbfa1, alpha1(I) procollagen, and osteocalcin synthesis. Moreover, it rendered the cells incapable of forming a mineralized matrix. These results strongly suggest that PPARgamma2 negatively regulates stromal cell plasticity by suppressing Osf2/Cbfa1 and osteoblast-like biosynthetic activity, while promoting terminal differentiation to adipocytes.
 ...
PMID:Inhibition of Osf2/Cbfa1 expression and terminal osteoblast differentiation by PPARgamma2. 1041 38

The objective of this study was to address the hypothesis that changes in extracellular pH alter collagen gene expression, collagen synthesis, and alkaline phosphatase activity in bone marrow stromal cells (BMSCs). Potential effects of pH on cell function are of particular importance for tissue engineering because considerable effort is being placed on engineering biodegradable polymers that may generate a local acidic microenvironment on degradation. Human and murine single-cell marrow suspensions were plated at a density of 2 x 10(4) cells/cm(2). After 7 days in culture, the pH of the culture medium was adjusted to one of six ranges: > or = 7.8, 7.5.-7.7, 7.2-7.4, 6.9-7.1, 6.6-6.8, or < or = 6.5. After 48 h of exposure to an altered pH, alkaline phosphatase activity and collagen synthesis decreased significantly with decreasing pH. This decrease was two-to threefold as pH decreased from 7.5 to 6.6. In contrast, alpha1(I) procollagen mRNA levels increased two- to threefold as pH was decreased. The trend in osteocalcin mRNA expression was opposite to that of collagen. Small shifts in extracellular pH led to significant changes in the ability of BMSCs to express markers of the osteoblast phenotype. These pH effects potentially relate to the microenvironment supplied by a tissue-engineering scaffold and suggest that degrading polymer scaffolds may influence the biologic activity of the cells in the immediate environment.
 ...
PMID:Effects of pH on human bone marrow stromal cells in vitro: implications for tissue engineering of bone. 1185 36