Cartilage oligomeric matrix protein associates with granulin-epithelin precursor (GEP) and potentiates GEP-stimulated chondrocyte proliferation

Development of macrophages of cyprinid fish

The innate immune responses of early vertebrates, such as bony fishes, play a central role in host defence against infectious diseases and one of the most important effector cells of innate immunity are macrophages. In order for macrophages to be effective in host defence they must be present at all times in the tissues of their host and importantly, the host must be capable of rapidly increasing macrophage numbers during times of need. Hematopoiesis is a process of formation and development of mature blood cells, including macrophages. Hematopoiesis is controlled by soluble factors known as cytokines, that influence changes in transcription factors within the target cells, resulting in cell fate changes and the final development of specific effector cells. The processes involved in macrophage development have been largely derived from mammalian model organisms. However, recent advancements have been made in the understanding of macrophage development in bony fish, a group of organisms that rely heavily on their innate immune defences. Our understanding of the growth factors involved in teleost macrophage development, as well as the receptors and regulatory mechanisms in place to control them has increased substantially. Furthermore, model organisms such as the zebrafish have emerged as important instruments in furthering our understanding of the transcriptional control of cell development in fish as well as in mammals. This review highlights the recent advancements in our understanding of teleost macrophage development. We focused on the growth factors identified to be important in the regulation of macrophage development from a progenitor cell into a functional macrophage and discuss the important transcription factors that have been identified to function in teleost hematopoiesis. We also describe the findings of in vivo studies that have reinforced observations made in vitro and have greatly improved the relevance and importance of using teleost fish as model organisms for studying developmental processes.

Ribozyme-mediated reduction of wild-type and mutant cartilage oligomeric matrix protein (COMP) mRNA and protein

Dominant-negative mutations in the homopentameric extracellular matrix glycoprotein cartilage oligomeric matrix protein (COMP) result in inappropriate intracellular retention of misfolded COMP in the rough endoplasmic reticulum of chondrocytes, causing chondrocyte cell death, which leads to two skeletal dysplasias: pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (EDM1). COMP null mice show no adverse effects on normal bone development and growth, suggesting a possible therapy involving removal of COMP mRNA. The goal of this study was to assess the ability of a hammerhead ribozyme (Ribo56, designed against the D469del mutation) to reduce COMP mRNA expression. In COS7 cells transfected with plasmids that overexpress wild-type or mutant COMP mRNA and Ribo56, the ribozyme reduced overexpressed normal COMP mRNA by 46% and mutant COMP mRNA by 56% in a dose-dependent manner. Surprisingly, the use of recombinant adenoviruses to deliver wild-type or mutant COMP mRNA and Ribo56 simultaneously into COS7 cells proved problematic for the activity of the ribozyme to reduce COMP expression. However, in normal human costochondral cells (hCCCs) infected only with adenoviruses expressing Ribo56, expression of endogenous wild-type COMP mRNA was reduced in a dose-dependent manner by 50%. In chondrocytes that contain heterozygous COMP mutations (D469del, G427E and D511Y) that cause PSACH, Ribo56 was more effective at reducing COMP mRNA (up to 70%). These results indicate that Ribo56 is effective at reducing mutant and wild-type COMP levels in cells and suggests a possible mode of therapy to reduce the mutant protein load.

The crystal structure of the signature domain of cartilage oligomeric matrix protein: implications for collagen, glycosaminoglycan and integrin binding

Cartilage oligomeric matrix protein (COMP), or thrombospondin-5 (TSP-5), is a secreted glycoprotein that is important for growth plate organization and function. Mutations in COMP cause two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (EDM1). In this study, we determined the structure of a recombinant protein that contains the last epidermal growth factor repeat, the type 3 repeats and the C-terminal domain (CTD) of COMP to 3.15-A resolution limit by X-ray crystallography. The CTD is a beta-sandwich that is composed of 15 antiparallel beta-strands, and the type 3 repeats are a contiguous series of calcium binding sites that associate with the CTD at multiple points. The crystal packing reveals an exposed potential metal-ion-dependent adhesion site (MIDAS) on one edge of the beta-sandwich that is common to all TSPs and may serve as a binding site for collagens and other ligands. Disease-causing mutations in COMP disrupt calcium binding, disulfide bond formation, intramolecular interactions, or sites for potential ligand binding. The structure presented here and its unique molecular packing in the crystal identify potential interactive sites for glycosaminoglycans, integrins, and collagens, which are key to cartilage structure and function.

The role of ADAMTS-7 and ADAMTS-12 in the pathogenesis of arthritis

Loss of articular cartilage caused by extracellular matrix breakdown is the hallmark of arthritis. Degradative fragments of cartilage oligomeric matrix protein (COMP) have been observed in arthritic patients. ADAMTS-7 and ADAMTS-12, two members of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family, have been associated with COMP degradation in vitro, and are significantly overexpressed in the cartilage and synovium of patients with rheumatoid arthritis. Recent studies have demonstrated the importance of COMP degradation by ADAMTS-7 and ADAMTS-12. Specifically, the size of COMP fragments generated by ADAMTS-7 or ADAMTS-12 is similar to that of COMP-degradative fragments seen in arthritic patients. In addition, antibodies against ADAMTS-7 or ADAMTS-12 dramatically inhibit tumor necrosis factor-induced and interleukin-1beta-induced COMP degradation in cartilage explants. Furthermore, suppression of ADAMTS-7 or ADAMTS-12 expression using the small interfering RNA silencing approach in human chondrocytes markedly prevents COMP degradation. COMP degradation mediated by ADAMTS-7 and ADAMTS-12 is inhibited by alpha(2)-macroglobulin. More significantly, granulin-epithelin precursor, a newly characterized chondrogenic growth factor, disturbs the interaction between COMP and ADAMTS-7 and ADAMTS-12, preventing COMP degradation by these enzymes. This Review summarizes the evidence demonstrating that ADAMTS-7 and ADAMTS-12 are newly identified enzymes responsible for COMP degradation in arthritis, and that alpha(2)-macroglobulin and granulin-epithelin precursor represent their endogenous inhibitors.

Analysis of cartilage oligomeric matrix protein (COMP) in synovial fluid, serum and urine from 51 racehorses with carpal bone fracture

We investigated the relationship between cartilage oligomeric matrix protein (COMP) levels in synovial fluid (SF), serum and urine and the development of osteochondral damage and osteophyte (OP) formation following intraarticular fractures of the carpus in racehorses in order to assess the clinical usefulness of COMP as a diagnostic biomarker of developmental osteoarthritis (OA). Two monoclonal antibodies (mAb clones 2A11 and 3C8) raised against equine COMP were shown to be capable of detecting the molecule in serum and urine as well as SF. Fifty-one samples were obtained from 26 OP-positive (OP(+)) and 25 OP-negative (OP(-)) racehorses with carpal bone fracture, in whom OP was ascertained arthroscopically and radiographically. The COMP measurements obtained using the two mAbs were highly correlated with each other in SF, serum, or urine. Horses with OP(+) showed a significantly higher [urinary COMP (microg)]/[urinary creatinine (mg)] ratio (4.94 +/- 5.10 and 1.46 +/- 1.19, using mAbs 2A11 and 3C8, respectively) than OP(-) horses (2.80 +/- 1.72 and 0.93 +/- 0.49, respectively). The relationship between serum and urine COMP levels and the period from injury to surgery were extrapolated using a polynomial expression. Measurement of COMP, especially in urine, has potential as a predictive marker of advanced OA following carpal bone fractures in racehorses.

COMP mutations: domain-dependent relationship between abnormal chondrocyte trafficking and clinical PSACH and MED phenotypes

Mutations in cartilage oligomeric matrix protein (COMP) produce clinical phenotypes ranging from the severe end of the spectrum, pseudoachondroplasia (PSACH), which is a dwarfing condition, to a mild condition, multiple epiphyseal dysplasia (MED). Patient chondrocytes have a unique morphology characterized by distended rER cisternae containing lamellar deposits of COMP and other extracellular matrix proteins. It has been difficult to determine why different mutations give rise to variable clinical phenotypes. Using our in vitro cell system, we previously demonstrated that the most common PSACH mutation, D469del, severely impedes trafficking of COMP and type IX collagen in chondrocytic cells, consistent with observations from patient cells. Here, we hypothesize that PSACH and MED mutations variably affect the cellular trafficking behavior of COMP and that the extent of defective trafficking correlates with clinical phenotype. Twelve different recombinant COMP mutations were expressed in rat chondrosarcoma cells and the percent cells with ER-retained COMP was assessed. For mutations in type 3 (T3) repeats, trafficking defects correlated with clinical phenotype; PSACH mutations had more cells retaining mutant COMP, while MED mutations had fewer. In contrast, the cellular trafficking pattern observed for mutations in the C-terminal globular domain (CTD) was not predictive of clinical phenotype. The results demonstrate that different COMP mutations in the T3 repeat domain have variable effects on intracellular transport, which correlate with clinical severity, while CTD mutations do not show such a correlation. These findings suggest that other unidentified factors contribute to the effect of the CTD mutations. J. Cell. Biochem. 103: 778-787, 2008. (c) 2007 Wiley-Liss, Inc.

Skeletal abnormalities in mice lacking extracellular matrix proteins, thrombospondin-1, thrombospondin-3, thrombospondin-5, and type IX collagen

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.