Ferenc Deák

The matrilins: a novel family of oligomeric extracellular matrix proteins.

The matrilin family at present has four members that all share a structure made up of von Willebrand factor A domains, epidermal growth factor-like domains and a coiled coil alpha-helical module. The first member of the family, matrilin-1 (previously called cartilage matrix protein or CMP), is expressed mainly in cartilage. Matrilin-3 has a similar tissue distribution, while matrilin-2 and -4 occur in a wide variety of extracellular matrices. Matrilin-1 is associated with cartilage proteoglycans as well as being a component of both collagen-dependent and collagen-independent fibrils and on the basis of the related structures other matrilins may play similar roles. The matrilin genes are strictly and differently regulated and their expression may serve as markers for cellular differentiation.

Matrilin-2, a Large, Oligomeric Matrix Protein, Is Expressed by a Great Variety of Cells and Forms Fibrillar Networks

Matrilin-2 is a member of the protein superfamily with von Willebrand factor type A-like modules. Mouse matrilin-2 cDNA fragments were expressed in 293-EBNA cells, and the protein was purified, characterized, and used to immunize rabbits. The affinity-purified antiserum detects matrilin-2 in dense and loose connective tissue structures, subepithelial connective tissue of the skin and digestive tract, specialized cartilages, and blood vessel walls. In situ hybridization of 35S-labeled riboprobes localizes the matrilin-2 mRNA to fibroblasts of dermis, tendon, ligaments, perichondrium, and periosteum; connective tissue elements in the heart; smooth muscle cells; and epithelia and loose connective tissue cells of the alimentary canal and respiratory tract. RNA blot hybridization and immunoblotting revealed both matrilin-2 mRNA and protein in cultures of a variety of cell types, confirming the tissue distribution. Alternative splicing affects a module unique for matrilin-2 in all of the above RNA sources. SDS-polyacrylamide gel electrophoresis and electron microscopy reveals matrilin-2 from tissue extracts and cell line cultures as a mixture of mono-, di-, tri-, and tetramers. Matrilin-2 is substituted with N-linked oligosaccharides but not with glycosaminoglycans. Because of other, yet unidentified, cell-type dependent posttranslational modifications, the monomer is heterogeneous in size. Immunofluorescence showed that matrilin-2 functions by forming an extracellular, filamentous network.

Coulomb dissociation of 11Li.

Kinematically complete measurements for Coulomb dissociation of [sup 11]Li into [sup 9]Li+2[ital n] were made at 28 MeV/nucleon. The [ital n]-[ital n] correlation function suggests a large source size for the two-neutron emission. The electromagnetic excitation spectrum of [sup 11]Li has a peak, as anticipated in low-energy dipole resonance models, but a large post-breakup Coulomb acceleration of the [sup 9]Li fragment is observed, indicating a very short lifetime of the excited state and favoring direct breakup as the dissociation mechanism.

Matrilin-2 interacts with itself and with other extracellular matrix proteins

Matrilin-2 is a component of extracellular filamentous networks. To study the interactions by which it can be integrated into such assemblies, full-length and truncated forms of matrilin-2 were recombinantly expressed in HEK-293 cells and purified from conditioned medium. The recombinant proteins, when used in interaction assays, showed affinity to matrilin-2 itself, but also to other collagenous and non-collagenous extracellular matrix proteins. The interaction between matrilin-2 and collagen I was studied in greater detail and could be shown to occur at distinct sites on the collagen I molecule and to have a K (D) of about 3 x 10(-8) M. Interactions with some non-collagenous protein ligands were even stronger, with matrilin-2 binding to fibrillin-2, fibronectin and laminin-1-nidogen-1 complexes, with K (D) values in the range of 10(-8)-10(-11) M. Co-localization of matrilin-2 with these ligands in the dermal-epidermal basement membrane, in the microfibrils extending from the basement membrane into the dermis, and in the dermal extracellular matrix, indicates a physiological relevance of the interactions in the assembly of supramolecular extracellular matrix structures.

Terminal differentiation of chondrocytes is arrested at distinct stages identified by their expression repertoire of marker genes

During endochondral bone formation, cells in the emerging cartilaginous model transit through a cascade of several chondrocyte differentiation stages, each characterized by a specific expression repertoire of matrix macromolecules, until, as a final step, the hypertrophic cartilage is replaced by bone. In many permanent cartilage tissues, however, late differentiation of chondrocytes does not occur, due to negative regulation by the environment of the cells. Here, addressing the reason for the difference between chondrocyte fates in the chicken embryo sternum, cells from the caudal and cranial part were cultured separately in serum-free agarose gels with complements defined earlier that either permit or prevent hypertrophic development. Total RNA was extracted using a novel protocol adapted to agarose cultures, and the temporal changes in developmental stage-specific mRNA expression were monitored by Northern hybridization and phosphor image analysis. Kinetic studies of the mRNA accumulation not only showed significant differences between the expression patterns of cranial and caudal cultures after recovery, but also revealed two checkpoints of chondrocyte differentiation in keeping with cartilage development in vivo. Terminal differentiation of caudal chondrocytes is blocked at the late proliferative stage (stage Ib), while the cranial cells can undergo hypertrophic development spontaneously. The differentiation of cranial chondrocytes is reversible, since they can re-assume an early proliferative (stage Ia) phenotype under the influence of insulin, fibroblast growth factor-2 and transforming growth factor-beta in combination. Thus, the expression pattern in the latter culture resembles that of articular chondrocytes. We also provide evidence that the capacities of caudal and sternal chondrocytes to progress from the late proliferative (stage Ib) to hypertrophic stage (stage II) correlate with their differing abilities to express the Indian hedgehog gene.

Expression of matrilin-1, -2 and -3 in developing mouse limbs and heart.

The expression of matrilin-1, -2 and -3 was studied in the heart and limb during mouse development. Matrilin-1 is transiently expressed in the heart between days 9.5 and 14.5 p.c. Matrilin-2 expression was detected in the heart from day 10.5 p.c. onwards. In the developing limb bud, both matrilin-1 and -3 were observed first at day 12.5 p.c. Throughout development matrilin-3 expression was strictly limited to cartilage, while matrilin-1 was also found in some other forms of connective tissue. Matrilin-2, albeit present around hypertrophic chondrocytes in the growth plate, was mainly expressed in non-skeletal structures. The complementary, but in part overlapping, expression of matrilins indicates the possibility for both redundant and unique functions among the members of this novel family of extracellular matrix proteins.

Expression of Matrilin-2 in Liver Cirrhosis and Hepatocellular Carcinoma

The recently described matrilin protein family is part of the extracellular matrix, their pathophysiological role as well as distribution in liver diseases, however, have not yet been studied. Considering that matrilins have been found to play role in cell growth and tissue remodeling, their possible involvement in carcinogenesis has been raised. The main objective of this study was to investigate the changes in matrilin-2 expression which is one of the main components of basement membranes. Thirty-five cases of surgically resected hepatocellular carcinomas, 35 corresponding surrounding liver tissues and 10 normal liver samples were used for the study. In 15 of 35 cases the tumor developed on the basis of cirrhosis. Matrilin-2 protein expression was detected in normal liver around bile ducts, portal blood vessels, while sinusoids were negative by immunohistochemistry. Cirrhotic surrounding tissue showed intensive matrilin-2 staining along the sinusoids. Tumorous neovasculature was found strongly positive by immunohistochemistry. No differences, however, were detected by morphometry regarding the amount of protein expression based on the grade of hepatocellular carcinomas. Real-time RT-PCR did not show significant differences in matrilin-2 mRNA expression between normal, cirrhotic and tumor samples. This suggests posttranslational modification of matrilin-2 manifesting in altered distribution in liver fibrosis. Our data indicate that matrilin-2 is a novel basement membrane component in the liver, which is synthetised during sinusoidal “capillarization” in cirrhosis and in hepatocellular carcinoma. This is the first report to describe the expression and distribution of matrilin-2 in human normal and cirrhotic liver as well as in hepatocellular carcinoma.

Identification of differentially expressed genes in the developing antler of red deer Cervus elaphus

Understanding the molecular mechanisms underlying bone development is a fundamental and fascinating problem in developmental biology, with significant medical implications. Here, we have identified the expression patterns for 36 genes that were characteristic or dominant in the consecutive cell differentiation zones (mesenchyme, precartilage, cartilage) of the tip section of the developing velvet antler of red deer Cervus elaphus. Two major functional groups of these genes clearly outlined: six genes linked to high metabolic demand and other five to tumor biology. Our study demonstrates the advantages of the antler as a source of mesenchymal markers, for distinguishing precartilage and cartilage by different gene expression patterns and for identifying genes involved in the robust bone development, a striking feature of the growing antler. Putative roles for “antler” genes that encode α-tropomyosine (tpm1), transgelin (tagln), annexin 2 (anxa2), phosphatidylethanolamine-binding protein (pebp) and apolipoprotein D (apoD) in intense but still controlled tissue proliferation are discussed.

Primary structure of human matrilin-2, chromosome location of the MATN2 gene and conservation of an AT-AC intron in matrilin genes

We isolated full-length cDNA clones for human matrilin-2, an oligomeric protein, which forms filamentous networks in the extracellular matrices of various tissues. The human matrilin-2 precursor is encoded by a 4.0-kb mRNA, it consists of 956 amino acids and shows 93% similarity to the mouse protein. Out of the two von Willebrand factor type A-like domains, the 10 epidermal growth factor-type modules, one unique sequence and the oligomerisation module, the first A domain is the most conserved. RT-PCR demonstrated wide expression of the gene in human cell lines of fibroblastic or epithelial origin. Alternative splicing affected only 19 amino acids in a 75-moiety-long segment, unique to matrilin-2. Isolation and analysis of the 3′ end of the gene revealed that the reason for alternative splicing is alternative 3′ splice site selection. Further, we identified in the human matrilin-2 gene a U12 type AT–AC intron between the last two exons encoding the oligomerisation domain. We mapped the matrilin-2 gene (MATN2) by fluorescence in situhybridization at chromosome position 8q22.

Altered expression of genes for kir ion channels in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a multifactorial disease characterized by left ventricular dilation that is associated with systolic dysfunction and increased action potential duration. The Kir2.x K⁺ channels (encoded by KCNJ genes) regulate the inward rectifier current (IK1) contributing to the final repolarization in cardiac muscle. Here, we describe the transitions in the gene expression profiles of 4 KCNJ genes from healthy or dilated cardiomyopathic human hearts. In the healthy adult ventricles, KCNJ2, KCNJ12, and KCNJ4 (Kir2.1-2.3, respectively) genes were expressed at high levels, while expression of the KCNJ14 (Kir2.4) gene was low. In DCM ventricles, the levels of Kir2.1 and Kir2.3 were upregulated, but those of Kir2.2 channels were downregulated. Additionally, the expression of the DLG1 gene coding for the synapse-associated protein 97 (SAP97) anchoring molecule exhibited a 2-fold decline with increasing age in normal hearts, and it was robustly downregulated in young DCM patients. These adaptations could offer a new aspect for the explanation of the generally observed physiological and molecular alterations found in DCM.