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Dibner J, Richards J, Kitchell M, Quiroz M. Metabolic Challenges and Early Bone Development. J APPL POULTRY RES 2007. [DOI: 10.1093/japr/16.1.126] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
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Wu LNY, Genge BR, Ishikawa Y, Ishikawa T, Wuthier RE. Effects of 24R,25- and 1α,25-dihydroxyvitamin D3 on mineralizing growth plate chondrocytes. J Cell Biochem 2006; 98:309-34. [PMID: 16408294 DOI: 10.1002/jcb.20767] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Time- and dosage-dependent effects of 1,25(OH)(2)D(3) and 24,25(OH)(2)D(3) on primary cultures of pre- and post-confluent avian growth plate (GP) chondrocytes were examined. Cultures were grown in either a serum-containing culture medium designed to closely mimic normal GP extracellular fluid (DATP5) or a commercially available serum-free media (HL-1) frequently used for studying skeletal cells. Hoechst DNA, Lowry protein, proteoglycan (PG), lactate dehydrogenase (LDH), and alkaline phosphatase (ALP) activity and calcium and phosphate mineral deposition in the extracellular matrix were measured. In preconfluent cultures grown in DATP5, physiological levels of 24,25(OH)(2)D(3) (0.10-10 nM) increased DNA, protein, and LDH activity significantly more than did 1,25(OH)(2)D(3) (0.01-1.0 nM). However, in HL-1, the reverse was true. Determining ratios of LDH and PG to DNA, protein, and each other, revealed that 1,25(OH)(2)D(3) specifically increased PG, whereas 24,25(OH)(2)D(3) increased LDH. Post-confluent cells were generally less responsive, especially to 24,25(OH)(2)D(3). The positive anabolic effects of 24,25(OH)(2)D(3) required serum-containing GP-fluid-like culture medium. In contrast, effects of 1,25(OH)(2)D(3) were most apparent in serum-free medium, but were still significant in serum-containing media. Administered to preconfluent cells in DATP5, 1,25(OH)(2)D(3) caused rapid, powerful, dosage-dependent inhibition of Ca(2+) and Pi deposition. The lowest level tested (0.01 nM) caused >70% inhibition during the initial stages of mineral deposition; higher levels of 1,25(OH)(2)D(3) caused progressively more profound and persistent reductions. In contrast, 24,25(OH)(2)D(3) increased mineral deposition 20-50%; it required >1 week, but the effects were specific, persistent, and largely dosage-independent. From a physiological perspective, these effects can be explained as follows: 1,25(OH)(2)D(3) levels rise in hypocalcemia; it stimulates gut absorption and releases Ca(2+) from bone to correct this deficiency. We now show that 1,25(OH)(2)D(3) also conserves Ca(2+) by inhibiting mineralization. The slow anabolic effects of 24,25(OH)(2)D(3)are consistent with its production under eucalcemic conditions which enable bone formation. These findings, which implicate serum-binding proteins and accumulation of PG in modulating accessibility of the metabolites to GP chondrocytes, also help explain some discrepancies previously reported in the literature.
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Affiliation(s)
- L N Y Wu
- Department of Chemistry and Biochemistry, University of South Carolina, 329 Graduate Science Research Center, Columbia, 29208, USA
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Yeh LCC, Lee JC. Co-transfection with the osteogenic protein (OP)-1 gene and the insulin-like growth factor (IGF)-I gene enhanced osteoblastic cell differentiation. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1763:57-63. [PMID: 16364466 DOI: 10.1016/j.bbamcr.2005.11.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2005] [Revised: 10/10/2005] [Accepted: 11/01/2005] [Indexed: 11/30/2022]
Abstract
Previous studies from this laboratory showed that the action of Osteogenic Protein-1 (OP-1, BMP-7) on osteoblastic cell differentiation could be enhanced by other protein factors, such as Insulin-like Growth Factor (IGF)-I. In the present study, we examined the effects of co-transfection with a combination of the OP-1 and the IGF-I gene on osteoblastic cell differentiation. The results first showed that fetal rat calvaria (FRC) cells transfected with the OP-1 gene under the control of the cytomegalovirus (CMV) promoter showed substantial production of the OP-1 protein. Transfected FRC cells also showed a DNA concentration-dependent increase in alkaline phosphatase (AP) activity, an osteoblastic cell differentiation marker. Von Kossa-positive nodules, a hallmark of bone formation in long-term cultures of bone-derived cells, were also observed in the transfected cells after 26 days in culture, whereas none were observed in control cells. Co-transfection of FRC cells with the combination of the OP-1 and the IGF-I gene resulted in a synergistic stimulation of AP activity. The increase was DNA dose-dependent. The current data show that transfection of OP-1 gene into osteoblastic cells stimulates osteoblastic cell differentiation in vitro. The study further demonstrates the feasibility of employing gene transfer of a second gene in combination with an OP-1 vector to synergistically enhance OP-1 activity.
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Affiliation(s)
- Lee-Chuan C Yeh
- Department of Biochemistry, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX, USA.
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Glowacki J, Yates KE, Maclean R, Mizuno S. In vitro engineering of cartilage: effects of serum substitutes, TGF-beta, and IL-1alpha. Orthod Craniofac Res 2005; 8:200-8. [PMID: 16022722 DOI: 10.1111/j.1601-6343.2005.00333.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
OBJECTIVES Cartilage is avascular and relatively homogeneous, making it an attractive tissue for in vitro histogenesis and surgical use in patients. We developed novel platform technologies in order to define the requirements for optimal in vitro chondrogenesis by isolated cells. In this series of studies, we tested alternatives to fetal bovine serum (FBS) and the effects of growth factors on formation of cartilage in 3D porous collagen sponges. DESIGN We used porous collagen sponges to assess the effects of serum substitutes and exogenous TGF-beta1 and IL-1alpha on chondrocytes (bovine articular chondrocytes, bACs) and on chondroinduced human dermal fibroblasts (hDFs). We determined the effects of low concentrations of FBS and two serum substitutes, Nutridoma and ITS(+3), on cellularity and matrix production. After culture for intervals, sponges were harvested for histological and biochemical measurement of cartilage-specific chondroitin 4-sulfate proteoglycan (C 4-S PG). RESULTS Cultured bACs showed equivalent growth in Nutridoma (1%) and 10% FBS. Both TGF-beta1 and IL-1alpha significantly stimulated accumulation of C 4-S PG by bACs in 3D porous collagen sponges. Many endogenous growth factors were upregulated in hDFs cultured with chondroinductive DBP. Addition of TGF-beta1 and IL-1alpha for 11 days significantly stimulated accumulation of C 4-S PG by hDFs cultured in DMEM with 1% Nutridoma. CONCLUSION Porous collagen sponges are supportive of chondrogenesis and of chondroinduction by DBP. Optimization of serum-free culture conditions, including growth factors, matrix components, and mechanical stimuli will expedite translation to wider clinical applications. Use of autogenous dermal fibroblasts pre-cultured with DBP and induced to chondrocytes offers an alternative to autogenous chondrocytes.
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Affiliation(s)
- J Glowacki
- Orthopedic Research, Brigham and Women's Hospital, Harvard Medical School and Harvard School of Dental Medicine, Boston, MA 02115, USA.
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Sanchez CP, He YZ. Daily or intermittent calcitriol administration during growth hormone therapy in rats with renal failure and advanced secondary hyperparathyroidism. J Am Soc Nephrol 2005; 16:929-38. [PMID: 15728789 DOI: 10.1681/asn.2003100878] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Growth hormone (GH) improves growth in children with chronic renal failure. The response to GH may be affected by the degree of secondary hyperparathyroidism and concurrent treatment with vitamin D. Forty-six rats underwent 5/6 nephrectomy (Nx) and were given a high-phosphorus diet (Nx-Phos) to induce advanced secondary hyperparathyroidism and divided into the following groups: (1) Nx-Phos (n = 10) received saline, (2) GH at 10 IU/kg per d (Nx-Phos+GH; n = 9), (3) GH and daily calcitriol (D) at 50 ng/kg per d (Nx-Phos+GH+daily D; n = 8), (4) GH and intermittent D (three times weekly) at 350 ng/kg per wk (Nx-Phos+GH+int D; n = 9), and (5) intact-control (n = 10). Serum parathyroid hormone (PTH) levels were elevated in Nx-Phos, but IGF-I levels did not change with growth hormone. Body length, tibial length, and growth plate width did not increase with either GH or calcitriol. Proliferating cell nuclear antigen staining, PTH/PTHrP receptor, bone morphogenetic protein-7, and fibroblast growth factor receptor-3 expression increased with GH alone or with intermittent calcitriol but were slightly diminished during daily calcitriol administration. GH enhanced IGF-I, IGF binding receptor-3, and GH receptor but declined with daily and intermittent calcitriol. Overall, there was no improvement in body length, tibial length, and growth plate width at the end of GH therapy, but selected markers of chondrocyte proliferation and chondrocyte differentiation increased, although these changes were attenuated by calcitriol. The combination of GH and calcitriol that is frequently used in children with renal failure and secondary hyperparathyroidism require further studies to evaluate the optimal dose and frequency of administration to increase linear growth and prevent bone disease.
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Affiliation(s)
- Cheryl P Sanchez
- Department of Pediatrics, University of Wisconsin Medical School, 3590 MSC/Pediatrics, 1300 University Avenue, Madison, WI 53706, USA.
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Wu LNY, Ishikawa Y, Genge BR, Wuthier RE. Chondrocytes isolated from tibial dyschondroplasia lesions and articular cartilage revert to a growth plate-like phenotype when cultured in vitro. J Cell Physiol 2005; 202:167-77. [PMID: 15389532 DOI: 10.1002/jcp.20105] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
We report here a comparative study of the development and behavior of chondrocytes isolated from normal growth plate tissue, tibial dyschondroplasic lesions, and from articular cartilage. The objective of these studies was to determine whether the properties exhibited by chondrocytes in dysplasic lesions or in articular cartilage were due to their cellular phenotype, their environment, or both. We had previously analyzed the electrolytes and amino acid levels in the extracellular fluid of avian growth plate chondrocytes. Using these data, we constructed a culture medium (DATP5) in which growth plate cells essentially recapitulate their normal behavior in vivo. Here, we used DATP5 to examine the behavior of chondrocytes isolated from lesions of tibial dyschondroplasia (TD). We found that once isolated from lesion and grown in this supportive medium, dysplasic chondrocytes behaved essentially like normal growth plate cells. These findings suggest that the cause of TD is local factors operating in vivo to prevent these cells from developing normally. With respect to articular chondrocytes, our data indicate that they more closely retain normal protein and proteoglycan synthesis when grown in serum-free media. These cells readily induced mineral formation in vitro, both in the presence and absence of serum. However, in serum-containing media, mineralization was significantly enhanced when the cells were exposed to retinoic acid (RA) or osteogenic protein-1 (OP-1). Our studies support previous work indicating the presence of autocrine factors produced by articular chondrocytes in vivo that prevent mineralization and preserve matrix integrity. The lack of inhibitory factors and the presence of supporting factors are likely reasons for the induction of mineralization by articular chondrocytes in vitro.
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Affiliation(s)
- Licia N Y Wu
- Department of Chemistry and Biochemistry, University of South Carolina, Graduate Science Research Center, Columbia, South Carolina 29208, USA
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Stanton LA, Sabari S, Sampaio AV, Underhill TM, Beier F. p38 MAP kinase signalling is required for hypertrophic chondrocyte differentiation. Biochem J 2004; 378:53-62. [PMID: 14594450 PMCID: PMC1223932 DOI: 10.1042/bj20030874] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2003] [Revised: 10/08/2003] [Accepted: 10/31/2003] [Indexed: 01/19/2023]
Abstract
Longitudinal growth of endochondral bones is accomplished through the co-ordinated proliferation and hypertrophic differentiation of growth plate chondrocytes. The molecular mechanisms and signalling cascades controlling these processes are not well understood. To analyse the expression and roles of p38 mitogen-activated protein kinases in this process, we have established a micromass system for the reproducible hypertrophic differentiation of mouse mesenchymal limb bud cells. Our results show that all four mammalian p38 kinase genes are expressed during the chondrogenic programme, as well as their upstream regulators MKK3 (mitogen-activated protein kinase kinase 3) and MKK6. Treatment of micromass cultures with pharmacological inhibitors of p38 results in a marked delay in hypertrophic differentiation in micromass cultures, indicating a requirement for p38 signalling in chondrocyte differentiation. Inhibition of p38 kinase activity leads to reduced and delayed induction of alkaline phosphatase activity and matrix mineralization. In addition, p38 inhibition causes reduced expression of hypertrophic marker genes such as collagen X, matrix metalloproteinase 13 and bone sialoprotein. The function of p38 in hypertrophic differentiation appears to be mediated, at least in part, by the transcription factor myocyte enhancer factor 2C. In summary, we have demonstrated a novel requirement for p38 signalling in hypertrophic differentiation of chondrocytes and identified myocyte enhancer factor 2C as an important regulator of chondrocyte gene expression.
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Affiliation(s)
- Lee-Anne Stanton
- CHIR Group in Skeletal Development and Remodeling, Department of Physiology and Pharmacology, University of Western Ontario, London, ON, Canada N6A 5C1
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Yeh LCC, Tsai AD, Lee JC. Osteogenic protein-1 (OP-1, BMP-7) induces osteoblastic cell differentiation of the pluripotent mesenchymal cell line C2C12. J Cell Biochem 2004; 87:292-304. [PMID: 12397611 DOI: 10.1002/jcb.10315] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The effects of Osteogenic Protein-1 (OP-1, BMP-7) on the differentiation of the pluripotent mesenchymal cell line, C2C12, were examined. OP-1 at 50 ng/ml partially inhibited myotube formation in C2C12 cells, while OP-1 at 200 ng/ml completely inhibited myotube formation and induced the formation of cells displaying osteoblastic morphology. High concentrations of OP-1 elevated the alkaline phosphatase (AP) activity dramatically, both as a function of time and OP-1 concentration. Osteocalcin (OC) mRNA expression was detected as early as 8 days in OP-1-treated cultures and subsequently increased considerably. Expression of bone sialoprotein (BSP) mRNA was low in control cultures and stimulated by OP-1. Collagen type I mRNA expression was enhanced by OP-1 during the early days in culture, but gradually decreased thereafter. MyoD mRNA expression, high in control cultures, was suppressed by OP-1 in a dose- and time-dependent manner. OP-1 enhanced ActR-I mRNA expression and significantly elevated the mRNA expressions of BMP-1, BMP-4, BMP-5, GDF-6, and GDF-8. The present results indicate that OP-1 is a potent inducer of C2C12 differentiation into osteoblastic cells.
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Affiliation(s)
- Lee-Chuan C Yeh
- Department of Biochemistry, The University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA.
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Yeh LCC, Tsai AD, Zavala MC, Lee JC. Cartilage-derived morphogenetic proteins enhance the osteogenic protein-1-induced osteoblastic cell differentiation of C2C12 cells. J Cell Physiol 2004; 201:401-8. [PMID: 15389555 DOI: 10.1002/jcp.20079] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Previous studies have shown that osteogenic protein-1 (OP-1; also known as BMP-7) induces differentiation of the pluripotent mesenchymal cell line C2C12 into osteoblastic cells. OP-1 also alters the steady-state levels of messenger RNA (mRNA) encoding for the cartilage-derived morphogenetic proteins (CDMPs) in C2C12 cells. In the present study, the effects of exogenous CDMPs on bone cell differentiation induced by OP-1 in C2C12 cells were examined. Exogenous CDMP-1, -2, and -3 synergistically and dose-dependently enhanced OP-1 action in stimulating alkaline phosphatase (AP) activity and osteocalcin (OC) mRNA expression. AP staining studies revealed that the combination of OP-1 and CDMP enhanced OP-1 action by stimulating those cells that had responded to OP-1 and not by activating additional cells. The combination did not change the mRNA expression of the BMPs and their receptors. CDMP-1 enhanced the suppression of the OP-1-induced expression of the myogeneic differentiation regulator MyoD. CDMP-1 and OP-1 alone stimulated Smad5 protein expression, but the combination of OP-1 and CDMP-1 stimulated synergistically Smad5 protein expression. Thus, one mechanism of the observed synergy involved enhancement of the induced Smad5 protein expression. At the same protein concentration, CDMP-1 is most potent in enhancing OP-1 activity in inducing osteoblastic cell differentiation of C2C12 cells. CDMP-3 is about 80% as potent as CDMP-1, and CDMP-2 is the least potent (about 50% of CDMP-1).
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Affiliation(s)
- Lee-Chuan C Yeh
- Department of Biochemistry, The University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA.
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Yeh LCC, Mallein-Gerin F, Lee JC. Differential effects of osteogenic protein-1 (BMP-7) on gene expression of BMP and GDF family members during differentiation of the mouse MC615 chondrocyte cells. J Cell Physiol 2002; 191:298-309. [PMID: 12012325 DOI: 10.1002/jcp.10094] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The mRNA expression patterns of several bone morphogenetic proteins (BMPs) and growth differentiation factors (GDFs) in long-term cultures of the clonal mouse chondrocyte cell line MC615 were examined. Distinct spatial and temporal patterns of expression of BMPs and GDFs were observed. The temporal orders of expression were correlated with those of several biochemical markers characteristic of chondrocytic cell differentiation. BMP-1, -2, -5, and -6 mRNA expression increased throughout the chondrogenic process and BMP-4 mRNA expression was not changed. GDF-1 and -3 mRNA expression increased throughout the chondrogenic process, and GDF-5, -6, -8, and -9 mRNA expressions were not changed. Effects of osteogenic protein-1 (OP-1, BMP-7) on the expression patterns of several other members of the BMP family and of the GDF family were also examined. OP-1 downregulated the BMP-1, -4, -5, and -6 mRNA expression by a maximal 3-, 5-, 2.5-, and 3-fold, respectively. The BMP-2 mRNA expression was not changed significantly by a low concentration of OP-1, but was increased at 200 ng/ml at day 7 of treatment. In contrast to the BMPs, OP-1 upregulated significantly the six GDF members examined (GDF-1, -3, -5, -6, -8, and -9) by three- to four-fold. Our findings demonstrate that OP-1 differentially regulates the mRNA expression of several related members of the BMP family and upregulates the mRNA expression of several members of the GDF family. The observations suggest that OP-1 action on cartilage differentiation involves a complex regulation of gene expression of several members of the BMP and the GDF family.
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Affiliation(s)
- Lee-Chuan C Yeh
- Department of Biochemistry, The University of Texas Health Science Center at San Antonio, Floyd Curl Drive, San Antonio, Texas 78229-3900, USA.
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Ballock RT, Zhou X, Mink LM, Chen DH, Mita BC. Both retinoic acid and 1,25(OH)2 vitamin D3 inhibit thyroid hormone-induced terminal differentiaton of growth plate chondrocytes. J Orthop Res 2001; 19:43-9. [PMID: 11332619 DOI: 10.1016/s0736-0266(00)00024-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Thyroid hormone has been known for over 50 years to be a potent regulator of skeletal maturation at the growth plate. The receptor for thyroid hormone has been discovered to be a member of the nuclear hormone receptor superfamily. Retinoic acid and 1,25(OH)2 vitamin D3, whose receptors also belong to this nuclear hormone receptor family, have been implicated in the control of chondrocyte proliferation and differentiation at the growth plate. Recent studies demonstrate that the receptors for thyroid hormone, retinoic acid, and vitamin D bind to a similar DNA response element in the promoter region of target genes and may form heterodimers to regulate gene transcription in target cells. These observations led us to hypothesize that the retinoic acid and/or vitamin D signaling pathways may interact with thyroid hormone signaling at the molecular level to modulate growth plate chondrocyte differentiation. Using a chemically defined, serum-free model of growth plate chondrocyte maturation, both all-trans retinoic acid and 1,25(OH)2 vitamin D3 markedly inhibited thyroid hormone-induced terminal differentiation in a dose-dependent manner. In the absence of thyroid hormone, retinoic acid stimulated alkaline phosphatase activity modestly at the highest dose used, however neither retinoic acid nor 1,25(OH)2 vitamin D3 induced expression of type X collagen mRNA. We conclude that retinoic acid and vitamin D are likely to be antagonists of thyroid hormone signaling in the growth plate.
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Affiliation(s)
- R T Ballock
- Department of Orthopaedics, Rainbow Babies and Childrens Hospital, University Hospitals of Cleveland, Case Western Reserve University, OH 44106, USA.
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Ishikawa Y, Genge BR, Wuthier RE, Wu LN. Thyroid hormone inhibits growth and stimulates terminal differentiation of epiphyseal growth plate chondrocytes. J Bone Miner Res 1998; 13:1398-411. [PMID: 9738512 DOI: 10.1359/jbmr.1998.13.9.1398] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
As a continuation of our studies on mineralization in epiphyseal growth plate (GP) chondrocyte cultures, the effects of tri-iodothyronine (T3) in both beta-glycerophosphate-containing, serum-free (HL-1) and beta-glycerophosphate-free, serum-containing medium (DATP5) were studied. The GP cells responded to T3 in a serum-, stage-, and dosage-dependent manner. Added at graded levels (0.1-10.0 nM) to preconfluent cultures (from day 7) in both HL-1 and DATP5, T3 caused progressive decreases in protein, collagen, and DNA synthesis but increased mineral deposition. In postconfluent cultures, these effects of T3 were generally muted. In preconfluent cultures, proteoglycan (PG) levels were not significantly affected in DATP5, although in HL-1 they were decreased by approximately 50%. In postconfluent cultures, T3 increased PG levels in DATP5 but had no effect in HL-1. In HL-1, alkaline phosphatase (ALP) activity was progressively increased by 200-500% in both pre- and postconfluent cultures. In DATP5 in preconfluent cultures, T3 initially stimulated but later suppressed ALP; in postconfluent cultures, T3 also transiently increased ALP but did not suppress activity upon longer exposure. The inhibitory effects of T3 on protein, PG, and DNA levels of GP chondrocytes suggest that in vivo its effects on bone growth must occur primarily after cellular proliferation. Apparently by binding to the 50 kDa thyroxine-binding globulin, which cannot penetrate the PG barrier, accessibility of T3 to GP chondrocytes is limited until the time of vascular penetration when its stimulatory effects on ALP and mineral deposition become critical for continued bone development.
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Affiliation(s)
- Y Ishikawa
- Department of Chemistry and Biochemistry, and School of Medicine, University of South Carolina, Columbia 29208, USA
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