Tenascin-Y is concentrated in adult nerve roots and has barrier properties in vitro

The Roles of Tenascins in Cardiovascular, Inflammatory, and Heritable Connective Tissue Diseases

Tenascins are a family of multifunctional extracellular matrix (ECM) glycoproteins with time- and tissue specific expression patterns during development, tissue homeostasis, and diseases. There are four family members (tenascin-C, -R, -X, -W) in vertebrates. Among them, tenascin-X (TNX) and tenascin-C (TNC) play important roles in human pathologies. TNX is expressed widely in loose connective tissues. TNX contributes to the stability and maintenance of the collagen network, and its absence causes classical-like Ehlers-Danlos syndrome (clEDS), a heritable connective tissue disorder. In contrast, TNC is specifically and transiently expressed upon pathological conditions such as inflammation, fibrosis, and cancer. There is growing evidence that TNC is involved in inflammatory processes with proinflammatory or anti-inflammatory activity in a context-dependent manner. In this review, we summarize the roles of these two tenascins, TNX and TNC, in cardiovascular and inflammatory diseases and in clEDS, and we discuss the functional consequences of the expression of these tenascins for tissue homeostasis.

The adhesion modulating properties of tenascin-W

Tenascins are extracellular matrix glycoproteins associated with cell motility, proliferation and differentiation. Tenascin-C inhibits cell spreading by binding to fibronectin; tenascin-R and tenascin-X also have anti-adhesive properties in vitro. Here we have studied the adhesion modulating properties of the most recently characterized tenascin, tenascin-W. C2C12 cells, a murine myoblast cell line, will form broad lamellipodia with stress fibers and focal adhesion complexes after culture on fibronectin. In contrast, C2C12 cells cultured on tenascin-W fail to spread and form stress fibers or focal adhesion complexes, and instead acquire a multipolar shape with short, actin-tipped pseudopodia. The same stellate morphology is observed when C2C12 cells are cultured on a mixture of fibronectin and tenascin-W, or on fibronectin in the presence of soluble tenascin-W. Tenascin-W combined with fibronectin also inhibits the spreading of mouse embryo fibroblasts when compared with cells cultured on fibronectin alone. The similarity between the adhesion modulating effects of tenascin-W and tenascin-C in vitro led us to study the possibility of tenascin-W compensating for tenascin-C in tenascin-C knockout mice, especially during epidermal wound healing. Dermal fibroblasts harvested from a tenascin-C knockout mouse express tenascin-W, but dermal fibroblasts taken from a wild type mouse do not. However, there is no upregulation of tenascin-W in the dermis of tenascin-C knockout mice, or in the granulation tissue of skin wounds in tenascin-C knockout animals. Similarly, tenascin-X is not upregulated in early wound granulation tissue in the tenascin-C knockout mice. Thus, tenascin-W is able to inhibit cell spreading in vitro and it is upregulated in dermal fibroblasts taken from the tenascin-C knockout mouse, but neither it nor tenascin-X are likely to compensate for missing tenascin-C during wound healing.

Tenascins and their implications in diseases and tissue mechanics

Tenascins are glycoproteins found in the extracellular matrix (ECM) of many tissues. Their role is not only to support the tissue structurally but also to regulate the fate of the different cell types populating the ECM. For instance, tenascins are required when active tissue modeling during embryogenesis or re-modeling after injury occurs. Interestingly, the four members of the tenascin family, tenascin-C, -X, -R and -W, show different and often mutually exclusive expression patterns. As a consequence, these structurally related proteins display distinct functions and are associated with distinct pathologies. The present review aims at presenting the four members of the tenascin family with respect to their structure, expression patterns and implications in diseases and tissue mechanics.

The regulation of tenascin expression by tissue microenvironments

Tenascins are a family of four extracellular matrix proteins: tenascin-C, X, R and W. The four members of the family have strikingly diverse patterns of expression during development and in the adult organism indicating independent mechanisms of regulation. In this review we illustrate that there are two types of tenascins, those that are significantly regulated by the tissue microenvironment (tenascin-C and tenascin-W), and those that have stabile, restricted expression patterns (tenascin-R and tenascin-X). We summarize what is known about the regulation of tenascin expression by transforming growth factor betas, fibroblast growth factors, platelet derived growth factors, as well as pro- and anti-inflammatory cytokines or hormones that either induce or inhibit expression of tenascins.

Avian tenascin-W: expression in smooth muscle and bone, and effects on calvarial cell spreading and adhesion in vitro

Tenascins are glycoproteins found primarily in the embryonic extracellular matrix. Here we have characterized the fourth and final member of the tenascin family in birds: tenascin-W. Avian tenascin-W has 3.5 epidermal growth factor-like repeats, 6 fibronectin type III domains, and a C-terminal fibrinogen-related domain. Immunohistochemistry reveals that avian tenascin-W is expressed transiently in developing smooth muscle, tendons, and ligaments, but the primary site of tenascin-W expression during development is in the extracellular matrix of bone and the cellular periosteum. In bony matrix, tenascin-W-coated fibrils partly overlap with fibrils that contain tenascin-C. The anti-tenascin-W also labels fibrils in cultures of osteogenic embryonic chicken calvarial cells. Primary calvarial cells cultured on purified tenascin-W become rounded, and fewer of these cells spread on fibronectin when tenascin-W is added to the medium when compared with calvarial cells cultured on fibronectin alone. Moreover, tenascin-W reduces the adhesion of calvarial cells to collagen type I in a shear force assay. We conclude that tenascin-W is likely to play a phylogenetically conserved role in developing bone and that it shares some of the basic anti-adhesive and matrix modulatory properties as tenascin-C.

Association study between the TNXB locus and schizophrenia in a Japanese population

The chromosome 6p21-24 region, which contains the human leukocyte antigen (HLA) region, has been suggested as an important locus for a susceptibility gene for schizophrenia. Recently, a significant association between schizophrenia and the TNXB locus, located immediately telomeric of the NOTCH4 locus in the HLA region, was observed. Few studies have further investigated the region in schizophrenia. In the present study, we investigated the region in a Japanese population. Subjects included 241 patients with schizophrenia and 290 controls. Twenty-six single nucleotide polymorphisms (SNPs) and the corresponding haplotypes were analyzed. As a result, exactly the same SNPs in the TNXB locus (rs1009382 and rs204887) as in the previous study were associated with schizophrenia (P = 0.034 and 0.034, respectively, uncorrected). A SNP (rs2071287) in the NOTCH4 locus and haplotype around it were also suggested to associate with the disease, consistent with another previous study (P = 0.041 and permutation P = 0.024, respectively, uncorrected). Although these associations became insignificant after Bonferroni correction, the findings might provide support for the association of the TNXB locus or its adjacent region of the NOTCH4 locus with schizophrenia.

Phylogenetic analysis of the tenascin gene family: evidence of origin early in the chordate lineage

BACKGROUND

Tenascins are a family of glycoproteins found primarily in the extracellular matrix of embryos where they help to regulate cell proliferation, adhesion and migration. In order to learn more about their origins and relationships to each other, as well as to clarify the nomenclature used to describe them, the tenascin genes of the urochordate Ciona intestinalis, the pufferfish Tetraodon nigroviridis and Takifugu rubripes and the frog Xenopus tropicalis were identified and their gene organization and predicted protein products compared with the previously characterized tenascins of amniotes.

RESULTS

A single tenascin gene was identified in the genome of C. intestinalis that encodes a polypeptide with domain features common to all vertebrate tenascins. Both pufferfish genomes encode five tenascin genes: two tenascin-C paralogs, a tenascin-R with domain organization identical to mammalian and avian tenascin-R, a small tenascin-X with previously undescribed GK repeats, and a tenascin-W. Four tenascin genes corresponding to tenascin-C, tenascin-R, tenascin-X and tenascin-W were also identified in the X. tropicalis genome. Multiple sequence alignment reveals that differences in the size of tenascin-W from various vertebrate classes can be explained by duplications of specific fibronectin type III domains. The duplicated domains are encoded on single exons and contain putative integrin-binding motifs. A phylogenetic tree based on the predicted amino acid sequences of the fibrinogen-related domains demonstrates that tenascin-C and tenascin-R are the most closely related vertebrate tenascins, with the most conserved repeat and domain organization. Taking all lines of evidence together, the data show that the tenascins referred to as tenascin-Y and tenascin-N are actually members of the tenascin-X and tenascin-W gene families, respectively.

CONCLUSION

The presence of a tenascin gene in urochordates but not other invertebrate phyla suggests that tenascins may be specific to chordates. Later genomic duplication events led to the appearance of four family members in vertebrates: tenascin-C, tenascin-R, tenascin-W and tenascin-X.

Murine tenascin-W: a novel mammalian tenascin expressed in kidney and at sites of bone and smooth muscle development

We cloned and characterized a novel member of the tenascin family of extracellular matrix proteins--the murine orthologue of zebrafish tenascin-W. Full-length recombinant tenascin-W was expressed and purified from mammalian cell cultures. Rotary shadowing followed by electron microscopy showed that tenascin-W forms hexabrachions. We studied its expression during development and in the adult by immunohistochemistry, in situ hybridization and immunoblotting. Tenascin-W is expressed during palate formation, osteogenesis and smooth muscle development. In the adult, tenascin-W is found in the kidney, cardiac semilunar valves, corneal limbus and periosteum. Tenascin-W and tenascin-C expression overlap in many of these areas. Bone-morphogenic-protein-2 treated C2C12 cells secrete tenascin-W and are able to adhere to and to extend actin-rich processes on a tenascin-W substratum. In vitro, cells bind to tenascin-W in an RGD-dependent manner. This adhesion is increased by transfection of alpha8 integrin, which localizes with tenascin-W in the periosteum and kidney.

Tenascin-R-deficient mice show structural alterations of symmetric perisomatic synapses in the CA1 region of the hippocampus

Accumulating evidence suggests that extracellular matrix (ECM) molecules play important roles in formation of synapses. Our previous electrophysiologic study of mice deficient in the extracellular matrix glycoprotein tenascin-R (TN-R) showed an impaired gamma-aminobutyric acid release at perisomatic inhibitory synapses in the CA1 pyramidal cell layer of the hippocampus. The present study investigated possible ultrastructural correlates of abnormal perisomatic inhibition. Topographic, morphometric, and stereologic methods were applied at the light and electron microscopic levels to quantify the density and spatial arrangement of cell bodies of CA1 pyramidal neurons and density and architecture of symmetric synapses formed on them in TN-R(-/-) and wild-type mice of different ages. The spatial arrangement of neuronal cell bodies in the CA1 pyramidal cell layer was found more diffuse and disordered in TN-R(-/-) mice than in wild-type animals. The coverage of the plasma membrane of pyramidal cell bodies by active zones of symmetric synapses was reduced by at least 40% in TN-R(-/-) animals compared with control animals. Further, the length of active zone profiles of perisomatic inhibitory synapses in the CA1 pyramidal cell layer was 8-14% smaller, whereas the number of active zones calculated per length unit of cell body profile was 30-40% smaller in TN-R mutants than in wild-type animals. The density and spatial arrangement of synaptic vesicles in the synaptic terminals provided ultrastructural evidence for reduced synaptic activity in TN-R mutants. Thus, TN-R appears to play an important role in the regulation of the number and architecture of perisomatic inhibitory synapses, which play crucial roles in the synchronization of neuronal activity and modulation of synaptic plasticity in the hippocampus.