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  • 1
    ISSN: 0730-2312
    Keywords: retinoic acid ; chondrocytes ; weight-bearing joints ; proteoglycan synthesis ; proteoglycan depletion ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: The effect of retinoic acid (RA) on primary cultures of growth plate chondrocytes obtained from weight-bearing joints was examined. Chondrocytes were isolated from the tibial epiphysis of 6- to 8-week-old broiler-strain chickens and cultured in either serum-containing or serum-free media. RA was administered at low levels either transiently or continuously after the cells had become established in culture. Effects of RA on cellular protein levels, alkaline phosphatase (AP) activity, synthesis of proteoglycan (PG), matrix calcification, cellular morphology, synthesis of tissue-specific types of collagen, and level of matrix metalloproteinase (MMP) activity were explored. RA treatment generally increased AP activity, and stimulated mineral deposition, especially if present continuously. RA also caused a shift in cell morphology from spherical/polygonal to spindle-like. This occurred in conjunction with a change in the type of collagen synthesized: type X and II collagens were decreased, while synthesis of type I collagen was increased. There was also a marked increase in the activity of MMP. Contrasting effects of continuous RA treatment on cellular protein levels were seen: they were enhanced in serum-containing media, but decreased in serum-free HL-1 media. Levels of RA as low as 10 nM significantly inhibited PG synthesis and caused depletion in the levels of PG in the medium and cell-matrix layer. Thus, in these appendicular chondrocytes, RA suppressed chondrocytic (PG, cartilage-specific collagens) and enhanced osteoblastic phenotype (cell morphology, type I collagen, alkaline phosphatase, and mineralization). J. Cell. Biochem. 65:209-230. © 1997 Wiley-Liss, Inc.
    Additional Material: 11 Ill.
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  • 2
    ISSN: 0730-2312
    Keywords: Rous sarcoma virus ; chondrocytes ; matrix calcification ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Endochondral bone formation involves the progression of epiphyseal growth plate chondrocytes through a sequence of developmental stages which include proliferation, differentiation, hypertrophy, and matrix calcification. To study this highly coordinated process, we infected growth plate chondrocytes with Rous sarcoma virus (RSV) and studied the effects of RSV transformation on cell proliferation, differentiation, matrix synthesis, and mineralization. The RSV-transformed chondrocytes exhibited a distinct bipolar, fibroblast-like morphology, while the mock-infected chondrocytes had a typical polygonal morphology. The RSV-transformed chondrocytes actively synthesized extracellular matrix proteins consisting mainly of type I collagen and fibronectin. RSV-transformed cells produced much less type X collagen than was produced by mock-transformed cells. There also was a significant reduction of proteoglycan levels secreted in both the cell-matrix layer and culture media from RSV-transformed chondrocytes. RSV-transformed chondrocytes expressed two- to- threefold more matrix metalloproteinase, while expressing only one-half to one-third of the alkaline phosphatase activity of mock infected cells. Finally, RSV-transformed chondrocytes failed to calcify the extracellular matrix, while mock-transformed cells deposited high levels of calcium and phosphate into their extracellular matrix. These results collectively indicate that RSV transformation disrupts the preprogrammed differentiation pattern of growth plate chondrocytes and inhibit chondrocyte terminal differentiation and mineralization. They also suggest that the expression of extracellular matrix proteins, type II and type X collagens, and the cartilage proteoglycans are important for chondrocyte terminal differentiation and matrix calcification. J. Cell. Biochem. 69:453-462, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
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  • 3
    ISSN: 0730-2312
    Keywords: chondrocytes ; TGF-β1 ; bFGF ; collagen ; fibronectin ; alkaline phosphatase ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Expression of several cellular and matrix proteins which increase significantly during the maturation of growth plate cartilage has been shown to be affected by various endocrine and autocrine factors. In the studies reported here, transforming growth factor-β (TGF-β1) and basic fibroblast growth factor (bFGF) were administered to primary cultures of avian growth plate chondrocytes at pre- or post-confluent stages to study the interplay that occurs between these factors in modulating chondrocytic phenotype. Added continuously to pre-confluent chondrocytes, TGF-β1 stimulated the cells to produce abundant extracellular matrix and multilayered cell growth; cell morphology was altered to a more spherical configuration. These effects were generally mimicked by bFGF, but cell shape was not affected. Administered together with TGF-β1, bFGF caused additive stimulation of protein synthesis, and alkaline phosphatase (AP) activity was markedly, but transiently enhanced. During this pre-confluent stage, TGF-β1 also increased fibronectin secretion into the culture medium. Added to post-confluent cells, TGF-β1 alone caused a dosage-dependent suppression of AP activity, but bFGF alone did not. Under these conditions, TGF-β1 and bFGF had little effect on general protein synthesis, but TGF-β1 alone caused large, dosage-dependent increases in synthesis of fibronectin, and to some extent type II and X collagens. Given together with bFGF, TGF-β1 synergistically increased secretion of fibronectin. These findings reveal that regulation of phenotypic expression in maturing growth plate chondrocytes involves complex interactions between growth factors that are determined by timing, level, continuity, and length of exposure.
    Additional Material: 12 Ill.
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  • 4
    ISSN: 0730-2312
    Keywords: chondrocytes ; osteogenic protein-1 ; retinoic acid ; mineralization ; ALP ; proteoglycans ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Osteogenic protein-1 (OP-1), a member of the TGF-β family of proteins, induces endochondral bone formation. Here we studied the effect of OP-1 on the development of primary cultures of avian growth plate (GP) chondrocytes in either serum-free or serum-containing medium, in the absence or presence of retinoic acid (RA). OP-1 was added on day 7 of culture and continued for 7 days, or until the cultures were harvested, typically on day 21. Alone, OP-1 caused ∼2-fold increase in proteoglycan synthesis into both the medium and the cell:matrix layer. Additionally, OP-1 caused a dosage-dependent increase in alkaline phosphatase (ALP) activity, and an increase in protein, when given from days 7-14 and examined on day 14. This stimulation was greater in cells grown in serum-free than in serum-containing media (3-5-fold vs. 2-3-fold increase in ALP; ∼40% vs. ∼20% increase in protein). Such stimulation of ALP activity and proteoglycan (PG) synthesis in cultured GP cells indicates that OP-1 elicits differentiation of chondrocytes. OP-1 minimally affected cell division (DNA content); however, a slight increase was seen when examined early in the culture. Alone, OP-1 increased mineral (Ca and Pi) content of the cultures by ∼2-fold in both types of media. As early as day 14, clusters of mineral encircled many of the OP-1 treated cells. Thus, as in vivo, OP-1 strongly promoted mineral formation by the cultured GP chondrocytes. When present together, OP-1 and RA generally blocked the action of the other. Separately OP-1 and RA each stimulated protein synthesis, ALP activity, and Ca2+ deposition; together they were inhibitory to each. Also, RA blocked the stimulation of PG synthesis induced by OP-1; whereas OP-1 decreased cell division engendered by RA. Thus, this GP chondrocyte culture system is a good model for studying factors that influence differentiation and mineral deposition during bone growth in vivo. J. Cell. Biochem. 67:498-513, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 10 Ill.
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  • 5
    ISSN: 0730-2312
    Keywords: chondrocytes ; cell culture ; mineralization ; calcospherites ; Ca and P mapping ; matrix vesicles ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Advances in the culture of mineralizing growth plate chondrocytes provided an opportunity to study endochondral calcification under controlled conditions. Here we report that these cultures synthesize large amounts of proteins characteristically associated with mineralization: type II and X collagens, sulfated proteoglycans, alkaline phosphatase, and the bone-related proteins, osteonectin and osteopontin. Certain chondrocytes appeared to accumulate large amounts of Ca2+ and Pi during the mineralization process: laser confocal imaging revealed high levels of intracellular Ca2+ in their periphery and X-ray microanalytical mapping revealed the presence of many Ca2+- and Pi-rich cell surface structures ranging from filamentous processes 0.14 ± 0.02 μm by 0.5-2.0 μm, to spherical globules 0.70 ± 0.27 μm in diameter. Removal of organic matter with alkaline sodium hypochlorite revealed numerous deposits of globular (0.77 ± 0.19 μm) mineral (calcospherites) in the lacunae around these cells. The size and spatial distribution of these mineral deposits closely corresponded to the Ca2+-rich cell surface blebs. The globular mineral progressively transformed into clusters of crystallites. Taken with earlier studies, these findings indicate that cellular uptake of Ca2+ and Pi leads to formation of complexes of amorphous calcium phosphate, membrane lipids, and proteins that are released as cell surface blebs analogous to matrix vesicles. These structures initiate development of crystalline mineral. Thus, the current findings support the concept that the peripheral intracellular accumulation of Ca2+ and Pi is directly involved in endochondral calcification.
    Additional Material: 13 Ill.
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