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Hintze V, Steplewski A, Ito H, Jensen DA, Rodeck U, Fertala A. Cells expressing partially unfolded R789C/p.R989C type II procollagen mutant associated with spondyloepiphyseal dysplasia undergo apoptosis. Hum Mutat 2008; 29:841-51. [PMID: 18383211 DOI: 10.1002/humu.20736] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Vera Hintze
- Department of Dermatology and Cutaneous Biology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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52
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Posey KL, Hankenson K, Veerisetty AC, Bornstein P, Lawler J, Hecht JT. Skeletal abnormalities in mice lacking extracellular matrix proteins, thrombospondin-1, thrombospondin-3, thrombospondin-5, and type IX collagen. THE AMERICAN JOURNAL OF PATHOLOGY 2008; 172:1664-74. [PMID: 18467703 DOI: 10.2353/ajpath.2008.071094] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Thrombospondin-5 (TSP5) is a large extracellular matrix glycoprotein found in musculoskeletal tissues. TSP5 mutations cause two skeletal dysplasias, pseudoachondroplasia and multiple epiphyseal dysplasia; both show a characteristic growth plate phenotype with retention of TSP5, type IX collagen (Col9), and matrillin-3 in the rough endoplasmic reticulum. Whereas most studies focus on defining the disease process, few functional studies have been performed. TSP5 knockout mice have no obvious skeletal abnormalities, suggesting that TSP5 is not essential in the growth plate and/or that other TSPs may compensate. In contrast, Col9 knockout mice have diminished matrillin-3 levels in the extracellular matrix and early-onset osteoarthritis. To define the roles of TSP1, TSP3, TSP5, and Col9 in the growth plate, all knockout and combinatorial strains were analyzed using histomorphometric techniques. While significant alterations in growth plate organization were found in certain single knockout mouse strains, skeletal growth was only mildly disturbed. In contrast, dramatic changes in growth plate organization in TSP3/5/Col9 knockout mice resulted in a 20% reduction in limb length, corresponding to similar short stature in humans. These studies show that type IX collagen may regulate growth plate width; TSP3, TSP5, and Col9 appear to contribute to growth plate organization; and TSP1 may help define the timing of growth plate closure when other extracellular proteins are absent.
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Affiliation(s)
- Karen L Posey
- Department of Pediatrics, University of Texas Medical School, 6431 Fannin, Houston, TX 77030, USA
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53
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Wang JJ, Guo YB. [Progress of molecular genetic research on pseudoachon-droplasia and multiple epiphyseal dysplasia]. YI CHUAN = HEREDITAS 2008; 30:537-542. [PMID: 18487141 DOI: 10.3724/sp.j.1005.2008.00537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) belong to the family of bone dysplasia disorders, which are both genetically and phenotypically heterogeneous. Both disorders are caused by mutations in the cartilage oligomeric matrix protein (COMP). COMP is a member of the thrombospondin (TSP) family, which plays an important role in skeletal development. In this paper, we mainly review the latest advances on the structure, function of COMP. We also discuss the types of COMP mutations, the detection methods and the relationship between the COMP gene and these two diseases.
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Affiliation(s)
- Jing-Jing Wang
- Department of Medical Genetics, Sun Yat-sen Medical College, Sun Yat-sen University, Guangzhou 510080, China.
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54
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Gagarina V, Carlberg AL, Pereira-Mouries L, Hall DJ. Cartilage Oligomeric Matrix Protein Protects Cells against Death by Elevating Members of the IAP Family of Survival Proteins. J Biol Chem 2008; 283:648-659. [DOI: 10.1074/jbc.m704035200] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Piróg-Garcia KA, Meadows RS, Knowles L, Heinegård D, Thornton DJ, Kadler KE, Boot-Handford RP, Briggs MD. Reduced cell proliferation and increased apoptosis are significant pathological mechanisms in a murine model of mild pseudoachondroplasia resulting from a mutation in the C-terminal domain of COMP. Hum Mol Genet 2007; 16:2072-88. [PMID: 17588960 PMCID: PMC2674228 DOI: 10.1093/hmg/ddm155] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Pseudoachondroplasia (PSACH) is one of the more common skeletal dysplasias and results from mutations in cartilage oligomeric matrix protein (COMP). Most COMP mutations identified to date cluster in the TSP3 repeat region of COMP and the mutant protein is retained in the rough endoplasmic reticulum (rER) of chondrocytes and may result in increased cell death. In contrast, the pathomolecular mechanism of PSACH resulting from C-terminal domain COMP mutations remain largely unknown. This study describes the generation and analysis of a murine model of mild PSACH resulting from a p.Thr583Met mutation in the C-terminal globular domain (CTD) of COMP. Mutant animals are normal at birth, but grow slower than their wild-type littermates and by 9 weeks of age they have mild short-limb dwarfism. Furthermore, by 16 months of age mutant animals exhibit severe degeneration of articular cartilage, which is consistent with early onset osteoarthritis seen in PSACH patients. In the growth plates of mutant mice the chondrocyte columns are sparser and poorly organized. Mutant COMP is secreted into the extracellular matrix, but its localization is disrupted along with the distribution of several COMP-binding proteins. Although mutant COMP is not retained within the rER there is an unfolded protein/cell stress response and chondrocyte proliferation is significantly reduced, while apoptosis is both increased and spatially dysregulated. Overall, these data suggests a mutation in the CTD of COMP exerts a dominant-negative effect on both intra- and extracellular processes. This ultimately affects the morphology and proliferation of growth plate chondrocytes, eventually leading to chondrodysplasia and reduced long bone growth.
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Affiliation(s)
- Katarzyna A. Piróg-Garcia
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, M13 9PT Manchester, UK
| | - Roger S. Meadows
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, M13 9PT Manchester, UK
| | - Lynette Knowles
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, M13 9PT Manchester, UK
| | - Dick Heinegård
- Biomedical Centre, Lund University, BMC C12, 221 84 Lund, Sweden
| | - David J. Thornton
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, M13 9PT Manchester, UK
| | - Karl E. Kadler
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, M13 9PT Manchester, UK
| | - Raymond P. Boot-Handford
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, M13 9PT Manchester, UK
| | - Michael D. Briggs
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, M13 9PT Manchester, UK
- To whom correspondence should be addressed. Tel: +44 1612755642; Fax: +44 1612755082;
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56
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Leighton MP, Nundlall S, Starborg T, Meadows RS, Suleman F, Knowles L, Wagener R, Thornton DJ, Kadler KE, Boot-Handford RP, Briggs MD. Decreased chondrocyte proliferation and dysregulated apoptosis in the cartilage growth plate are key features of a murine model of epiphyseal dysplasia caused by a matn3 mutation. Hum Mol Genet 2007; 16:1728-41. [PMID: 17517694 PMCID: PMC2674230 DOI: 10.1093/hmg/ddm121] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Disruption to endochondral ossification leads to delayed and irregular bone formation and can result in a heterogeneous group of genetic disorders known as the chondrodysplasias. One such disorder, multiple epiphyseal dysplasia (MED), is characterized by mild dwarfism and early-onset osteoarthritis and can result from mutations in the gene encoding matrilin-3 (MATN3). To determine the disease mechanisms that underpin the pathophysiology of MED we generated a murine model of epiphyseal dysplasia by knocking-in a matn3 mutation. Mice that are homozygous for the mutation develop a progressive dysplasia and have short-limbed dwarfism that is consistent in severity with the relevant human phenotype. Mutant matrilin-3 is retained within the rough endoplasmic reticulum of chondrocytes and is associated with an unfolded protein response. Eventually, there is reduced proliferation and spatially dysregulated apoptosis of chondrocytes in the cartilage growth plate, which is likely to be the cause of disrupted linear bone growth and the resulting short-limbed dwarfism in the mutant mice.
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Affiliation(s)
- Matthew P. Leighton
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Seema Nundlall
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Tobias Starborg
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Roger S. Meadows
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Farhana Suleman
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Lynette Knowles
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | | | - David J. Thornton
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Karl E. Kadler
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Raymond P. Boot-Handford
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Michael D. Briggs
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
- To whom correspondence should be addressed. Tel: +44 1612755642; Fax: +44 1612755082;
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57
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Merritt TM, Bick R, Poindexter BJ, Alcorn JL, Hecht JT. Unique matrix structure in the rough endoplasmic reticulum cisternae of pseudoachondroplasia chondrocytes. THE AMERICAN JOURNAL OF PATHOLOGY 2007; 170:293-300. [PMID: 17200202 PMCID: PMC1762700 DOI: 10.2353/ajpath.2007.060530] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Mutations in cartilage oligomeric matrix protein (COMP) cause two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED/EDM1). Because COMP exists as a homopentamer, only one mutant COMP subunit may result in an abnormal complex that is accumulated in expanded rough endoplasmic reticulum (rER) cisternae, a hallmark of PSACH. Type IX collagen and matrilin-3 (MATN3), also accumulate in the rER cisternae of PSACH chondrocytes, but it is unknown how mutant COMP interacts with these proteins. The studies herein focus on defining the organization of these intracellularly retained proteins using fluorescence deconvolution microscopy. A unique matrix organization was identified in which type II procollagen formed a central core surrounded by a protein network of mutant COMP, type IX collagen, and MATN3. This pattern of matrix organization was found in multiple cisternae from single chondrocytes and in chondrocytes with different COMP mutations, indicating a common pattern of interaction. This suggests that stalling of mutant COMP and an interaction between mutant COMP and type II procollagen are initiating events in the assembly of matrix in the rER, possibly explaining why the material is not readily cleared from the rER. Altogether, these data suggest that mutant COMP initiates and perhaps catalyzes premature intracellular matrix assembly.
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Affiliation(s)
- Thomas M Merritt
- Department of Pediatrics, University of Texas-Houston Medical School, 6431 Fannin St., MSB 3.136, Houston, TX 77030, USA
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58
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Weirich C, Keene DR, Kirsch K, Heil M, Neumann E, Dinser R. Expression of PSACH-associated mutant COMP in tendon fibroblasts leads to increased apoptotic cell death irrespective of the secretory characteristics of mutant COMP. Matrix Biol 2007; 26:314-23. [PMID: 17307347 DOI: 10.1016/j.matbio.2007.01.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Revised: 11/17/2006] [Accepted: 01/08/2007] [Indexed: 10/23/2022]
Abstract
OBJECTIVE Pseudoachondroplasia (PSACH) is a dominantly inherited chondrodysplasia associated with mutations of cartilage oligomeric matrix protein (COMP), characterized clinically by disproportionate dwarfism and laxity of joints and ligaments. Studies in chondrocytes and cartilage biopsies suggest that the cartilage disease is caused by retention of mutant COMP in the endoplasmic reticulum of chondrocytes and by disruption of the collagen network of the extracellular matrix. The pathogenesis of the tendon disease remains unclear in the absence of a cell culture model, with available tendon biopsies leading to conflicting results with respect to the intracellular retention of mutant COMP. METHODS We established a cell culture model using adenoviral gene transfer in tendon fibroblast cultures. We compared the effect of expression of three PSACH-associated COMP mutants and the wildtype protein on COMP secretion, matrix composition and cellular viability. RESULTS Our results show that mutants D475N and D469Delta are retained within the endoplasmic reticulum of tendon cells similar to what is known from chondrocytes, whereas mutant H587R is secreted like wildtype COMP. In spite of this difference, the collagen I matrix formed in culture appears disturbed for all three mutants. All COMP-mutants induce apoptotic cell death irrespective of their differing secretion patterns. CONCLUSION Pathogenic pathways leading to tendon disease in humans appear to be heterogeneous between different COMP mutants.
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Affiliation(s)
- Christian Weirich
- Department of Internal Medicine and Rheumatology, Justus-Liebig-University of Giessen, Kerckhoff Hospital, Benekestrasse 2-8, D-61231 Bad Nauheim, Germany
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59
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Schmitz M, Becker A, Schmitz A, Weirich C, Paulsson M, Zaucke F, Dinser R. Disruption of Extracellular Matrix Structure May Cause Pseudoachondroplasia Phenotypes in the Absence of Impaired Cartilage Oligomeric Matrix Protein Secretion. J Biol Chem 2006; 281:32587-95. [PMID: 16928687 DOI: 10.1074/jbc.m601976200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Pseudoachondroplasia and multiple epiphyseal dysplasia are two dominantly inherited chondrodysplasias associated with mutations in cartilage oligomeric matrix protein (COMP). The rarely available patient biopsies show lamellar inclusions in the endoplasmic reticulum. We studied the pathogenesis of these chondrodysplasias by expressing several disease-causing COMP mutations in bovine primary chondrocytes and found that COMP-associated chondrodysplasias are not exclusively storage diseases. Although COMP carrying the mutations D469Delta and D475N was retained within the endoplasmic reticulum, secretion of COMP H587R was only slightly retarded. All pseudoachondroplasia mutations impair cellular viability and cause a disruption of the extracellular matrix formed in alginate culture irrespective of the degree of cellular retention. The mutation D361Y associated with the clinically milder disease multiple epiphyseal dysplasia gave mild retention and limited matrix alterations, but the transfected cells showed normal viability. The effect of mutated COMP on matrix formation and cell-matrix interaction may be a major element in the pathogenesis of COMP-associated chondrodysplasias.
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Affiliation(s)
- Markus Schmitz
- Center for Biochemistry and Center for Molecular Medicine, Medical Faculty, University of Cologne, Joseph-Stelzmann-Strasse 52, D-50931 Cologne
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60
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Merritt TM, Alcorn JL, Haynes R, Hecht JT. Expression of mutant cartilage oligomeric matrix protein in human chondrocytes induces the pseudoachondroplasia phenotype. J Orthop Res 2006; 24:700-7. [PMID: 16514635 DOI: 10.1002/jor.20100] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Over 70 mutations in the cartilage oligomeric matrix protein (COMP), a large extracellular pentameric glycoprotein synthesized by chondrocytes, have been identified as causing two skeletal dysplasias: multiple epiphyseal dysplasia (MED/EDM1), and a dwarfing condition, pseudoachondroplasia (PSACH). These mutations induce misfolding of intracellular COMP, resulting in retention of the protein in the rough endoplasmic reticulum (rER) of chondrocytes. This accumulation of COMP in the rER creates the phenotypic enlarged rER cisternae in the cells, which is believed to compromise chondrocyte function and eventually cause cell death. To study the molecular mechanisms involved with the disease, we sought to develop an in vitro model that recapitulates the PSACH phenotype. Normal human chondrocytes were transfected with wildtype (wt-) COMP or with mutant COMP (D469del; mt-) recombinant adenoviruses and grown in a nonattachment redifferentiating culture system that provides an environment allowing formation of a differentiated chondrocyte nodule. Visualization of normal cells expressing COMP suggested the hallmarks of the PSACH phenotype. Mutant COMP expressed in normal cells was retained in enlarged rER cisternae, which also retained IX collagen (COL9) and matrilin-3 (MATN3). Although these proteins were secreted normally into the ECM of the wt-COMP nodules, reduced secretion of these proteins was observed in nodules composed of cells transfected with mt-COMP. The findings complement those found in chondrocytes from PSACH patient growth plates. This new model system allows for production of PSACH chondrocyte pathology in normal costochondral chondrocytes and can be used for future mechanistic and potential gene therapy studies.
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Affiliation(s)
- Thomas M Merritt
- Department of Pediatrics, University of Texas Medical School at Houston, University of Texas, 6431 Fannin Street, MSB 3.136, Houston, Texas 77030, USA
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61
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Posey KL, Davies S, Bales ES, Haynes R, Sandell LJ, Hecht JT. In vivo human Cartilage Oligomeric Matrix Protein (COMP) promoter activity. Matrix Biol 2005; 24:539-49. [PMID: 16214313 DOI: 10.1016/j.matbio.2005.07.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2005] [Revised: 07/27/2005] [Accepted: 07/28/2005] [Indexed: 11/26/2022]
Abstract
Cartilage oligomeric matrix protein (COMP) is a large extracellular matrix protein whose function is unknown. Mutations in COMP cause pseudoachondroplasia and multiple epiphyseal dysplasia, two skeletal dysplasias which are associated with intracellular retention of COMP in chondrocytes. In contrast, COMP null mice are normal suggesting gene redundancy or that the detrimental effect is associated with mutant COMP rather than the absence of functional COMP. To define the elements that regulate COMP transcription and tissue-specificity, we have evaluated the human COMP promoter driving fusion gene expression in vitro and in vivo. COMP promoter activity is higher in rat chondrosarcoma cells (RCS) than in a fibroblast cell line. In RCS cells, expression of a reporter gene containing 1.7 kb of the human COMP promoter was three-fold higher than all shorter COMP promoter constructs. In transgenic mice, 1.7 kb of the human COMP promoter is active early in development in the limbs, spine, and eye. As development progresses, promoter activity diminishes in the eye and migrates from the center to the ends of the long bones. On the other hand, while 375 bp of the human COMP promoter is sufficient for proper tissue-specific expression, levels are less than those found with the 1.7-COMP promoter. The expression pattern of both promoters recapitulates endogenous cartilage COMP expression in mice. Our findings indicate that the elements required for chondrocyte-specific expression lie within 375 bp of the translational start site, while DNA enhancer elements are located between 1.0 to 1.7 kb.
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Affiliation(s)
- Karen L Posey
- Department of Pediatrics, University of Texas Medical School at Houston, 6431 Fannin, 77030, USA
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62
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Chen TLL, Stevens JW, Cole WG, Hecht JT, Vertel BM. Cell-type specific trafficking of expressed mutant COMP in a cell culture model for PSACH. Matrix Biol 2005; 23:433-44. [PMID: 15579310 DOI: 10.1016/j.matbio.2004.09.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2004] [Revised: 09/23/2004] [Accepted: 09/23/2004] [Indexed: 11/26/2022]
Abstract
Pseudoachondroplasia (PSACH) is an autosomal dominant disease that mainly affects cartilage, resulting in skeletal dysplasias and early onset osteoarthritis. PSACH is caused by mutations in the cartilage oligomeric matrix protein (COMP) gene. PSACH chondrocytes accumulate unique COMP-containing lamellar structures in an expanded rough endoplasmic reticulum (rER). Although COMP is also present in tendon extracellular matrix (ECM), it does not accumulate in PSACH tendon cells, suggesting the disease involves a chondrocyte-specific trafficking problem. To investigate putative cell-specific trafficking differences, we generated a cell culture model utilizing expression of the common DeltaD469 COMP mutation. In rat chondrosarcoma (RCS) cells, we find delayed secretion and ER accumulation of DeltaD469 COMP, paralleling the altered trafficking defect in PSACH chondrocytes. Non-chondrocytic COS-1 cells, in contrast, efficiently trafficked and secreted both mutant and wild-type COMP. In chondrocytic cells, expression of DeltaD469 COMP led to ER accumulation of type IX collagen, but did not affect aggrecan trafficking. Endogenous rat COMP accumulated in the ER along with expressed DeltaD469 COMP in a stably expressing RCS clone, consistent with the dominant negative effect of PSACH. When these stably expressing cells were cultured to promote ECM deposition, the small amount of secreted mutant COMP disrupted assembly of the normal fibrillar meshwork and caused irregular aggregates of COMP and type IX collagen to form. Thus, in a new model that reflects the cellular pathology of PSACH, we establish trafficking differences for mutant COMP in chondrocytic and non-chondrocytic cells and demonstrate that mutant COMP interferes with assembly of a normal ECM.
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Affiliation(s)
- Tung-Ling L Chen
- Department of Cell Biology and Anatomy, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL 60064, USA
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63
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Posey KL, Hayes E, Haynes R, Hecht JT. Role of TSP-5/COMP in pseudoachondroplasia. Int J Biochem Cell Biol 2004; 36:1005-12. [PMID: 15094116 DOI: 10.1016/j.biocel.2004.01.011] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2003] [Revised: 01/07/2004] [Accepted: 01/13/2004] [Indexed: 11/15/2022]
Abstract
Pseudoachondroplasia (PSACH) is a well-characterized dwarfing condition associated with disproportionate short stature, abnormal joints and osteoarthritis requiring joint replacement. PSACH is caused by mutations in cartilage oligomeric matrix protein (COMP). COMP, the fifth member of the thrombospondin (TSP) gene family, is a pentameric protein found primarily in the extracellular matrix of musculoskeletal tissues. Functional studies have shown that COMP binds types II and IX collagens but the role of COMP in the extracellular matrix remains to be defined. Mutations in COMP interfere with calcium-binding and protein conformation. PSACH growth plate and growth plate chondrocytes studies indicate that COMP mutations have a dominant negative effect with both COMP and type IX collagen being retained in large rER cisternae. This massive retention causes impaired chondrocyte function with little COMP secreted into the matrix and premature loss of chondrocytes. Deficiency of linear growth results from loss of chondrocytes from the growth plate. Secondarily, the matrix contains minimal COMP, which may be normal and/or mutant, and little type IX collagen. This deficiency results in abnormal joints that are easily eroded and cause painful osteoarthritis. Unlike other misfolded proteins that are targeted for degradation, much of the retained COMP escapes degradation, compromises cell function, and causes cell death. Gene therapy will need to target the reduction of COMP in order to restore normal chondrocyte function and longevity.
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Affiliation(s)
- Karen L Posey
- Department of Pediatrics, Medical School at Houston, University of Texas Health Science Center, 6431 Fannin, Room MSB 3.306, Houston, TX 77030, USA
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