The tenascin gene family—versatile glycoproteins implicated in neural pattern formation and regeneration

Self-assembling multidomain peptide hydrogels accelerate peripheral nerve regeneration after crush injury

Multidomain peptide (MDP) hydrogels are a class of self-assembling materials that have been shown to elicit beneficial responses for soft tissue regeneration. However, their capacity to promote nervous system regeneration remains unknown. The peripheral nervous system (PNS) substantially recovers after injury, partly due to the abundance of extracellular matrix (ECM) components in its basal lamina. However, severe peripheral nerve injuries that significantly damage the ECM continue to be a major clinical challenge as they occur at a high rate and can be extremely detrimental to patients' quality of life. In this study, a panel of eight MDPs were designed to contain various motifs mimicking extracellular matrix components and growth factors and successfully self-assembled into injectable, nanofibrous hydrogels. Using an in vitro screening system, various lysine based MDPs were found to enhance neurite outgrowth. To test their capacity to promote nerve regeneration in vivo, rat sciatic nerve crush injury was performed with MDP hydrogels injected directly into the injury sites. MDP hydrogels were found to enhance macrophage recruitment to the injury site and degrade efficiently over time. Rats that were injected with the MDP hydrogel K2 and laminin motif-containing MDPs K2-IIKDI and K2-IKVAV were found to have significantly accelerated functional recovery and remyelination compared to those injected with HBSS or other MDPs. These results demonstrate that MDPs enhance neurite outgrowth and promote a multicellular pro-regenerative response in peripheral nerve injury. This study provides important insights into the potential of MDPs as biomaterials for nerve regeneration and other clinical applications.

Fibronectin domains of extracellular matrix molecule tenascin-C modulate hippocampal learning and synaptic plasticity

The extracellular matrix molecule tenascin-C (TN-C) has been shown to be involved in hippocampal synaptic plasticity in vitro. Here, we describe a deficit in hippocampus-dependent contextual memory in TN-C-deficient mice using the step-down avoidance paradigm. We further show that a fragment of TN-C containing the fibronectin type-III repeats 6-8 (FN6-8), but not a fragment containing repeats 3-5, bound to pyramidal and granule cell somata in the hippocampal formation of C57BL/6J mice and repelled axons of pyramidal neurons when presented as a border in vitro. Injection of the FN6-8 fragment into the hippocampus inhibited retention of memory in the step-down paradigm and reduced levels of long-term potentiation in the CA1 region of the hippocampus. In summary, our data show that TN-C is involved in hippocampus-dependent contextual memory and synaptic plasticity and identify the FN6-8 domain as one of molecular determinants mediating these functions.

Myelination and behaviour of tenascin-C null transgenic mice

The extracellular matrix glycoprotein tenascin-C is widely expressed during development and repair, making it surprising that few abnormalities have been found in transgenic mice lacking this molecule. We have therefore re-examined the transgenic mice described by Saga et al. [Saga, Y., Yagi, T., Ikawa, Y., Sakakura, T. & Aizawa, S. (1992) Genes Dev., 6 1821-1831] in which tenascin-C was knocked-out by homologous recombination, focusing on two aspects of the nervous system likely to reveal any abnormalities that might follow the loss of tenascin-C. First, we have determined the pattern of myelin and distribution of oligodendrocyte precursor cells in those areas, such as the optic nerve and retina where local concentrations of tenascin-C have been proposed to act as barriers to oligodendrocyte precursor migration and so prevent inappropriate myelination. Secondly, we have examined the behaviour of the mice in a number of well-characterized tests, e.g. beam-walking, passive avoidance and the Morris water maze. We find no abnormalities of myelination or oligodendrocyte precursor distribution in adult mice, showing that local concentrations of tenascin-C are not the sole mechanism responsible for the pattern of myelination in these regions of CNS. However, we do find a number of behavioural abnormalities in these mice and show that hyperlocomotion and deficits in coordination during beam walking can be ascribed to tenascin-C deficiency. The effects on coordination are, however, not seen on a 129 genetic background. Taken together, these results significantly extend the phenotype associated with tenascin-C deficiency but argue against a role in myelination.

The subependymal layer in rodents: a site of structural plasticity and cell migration in the adult mammalian brain

The persistence of neurogenesis and structural plasticity was believed until recently to be restricted to lower vertebrates and songbirds. Nevertheless, it has now been ascertained that these phenomena can occur in the adult mammalian nervous system, at least in three distinct sites: the olfactory neuroepithelium of the nasal mucosa and two brain regions, namely, the hippocampal dentate gyrus and the olfactory bulb. The newly generated cells of the olfactory bulb originate from the subependymal layer, a remnant of the primitive subventricular zone persisting in the adult forebrain. Besides being characterized by high rates of cell proliferation, the subependymal layer is a site of long-distance tangential cell migration, wherein migrating cells form chains enwrapped by a particular type of astrocytes. These glial cells give rise to channels (glial tubes) that separate single chains from the surrounding mature tissue. The cellular composition and the pattern of cell migration in the mammalian subependymal layer appear to be quite different in neonatal and adult animals, changing strikingly in the postnatal period. Other features of uniqueness involve the capability of neuronal precursors to divide while undergoing migration and the presence of multipotent stem cells. Thus, the subependymal layer is an area of the adult mammalian brain endowed with a cohort of phenomena proper of neural development, persisting into (and adapted to) the fully mature nervous tissue. Such features make this system an optimal model to unravel mechanisms permitting highly dynamic structural plasticity during adulthood, in the perspective of providing strategies for possible brain repair.

Mucosal tenascin C content in inflammatory and neoplastic diseases of the large bowel

PURPOSE

Tenascin C is a glycoprotein of the extracellular matrix. It is upregulated during embryologic development, wound healing, and under conditions of normal and neoplastic growth. Most available data on tenascin C expression in tissues is based on immunohistologic studies. The present study was designed to quantify tissue concentrations in patients with inflammatory and neoplastic diseases of the large bowel.

METHODS

Fifty patients with ulcerative colitis, 19 patients suffering from familiar adenomatous polyposis without malignant transformation, and 69 patients with colorectal carcinoma were investigated. Tenascin C concentrations in tissue extracts were determined by semiquantitative Western blotting.

RESULTS

The tenascin C tissue concentration of normal mucosa was 2.6 +/- 3.4 microg/mg (n = 55), 2.9 +/- 2.1 microg/mg in colorectal adenomas (n = 19), 7.5 +/- 4.7 microg/mg in ulcerative colitis (n = 50), and 18 +/- 15 microg/mg in colorectal carcinomas (n = 69; mean +/- standard deviation). In ulcerative colitis, the mucosal tenascin C content correlated with histopathologic disease activity. No differences were found between subgroups of adenomas or carcinomas.

CONCLUSIONS

Tenascin C tissue concentrations were not altered in adenomas, slightly elevated in ulcerative colitis, and substantially increased in colorectal carcinomas. Although less useful as a diagnostic parameter, tenascin C tissue levels serve as an instrument for assessing the activity of stromal remodeling in large-bowel diseases generally. Specifically, they may reflect disease activity in ulcerative colitis.

Up-regulation of astrocyte-derived tenascin-C correlates with neurite outgrowth in the rat dentate gyrus after unilateral entorhinal cortex lesion

The extracellular matrix protein tenascin-C has been implicated in the regulation of axonal growth. Using unilateral entorhinal cortex lesions, which induce a massive sprouting response in the denervated outer molecular layer of the rat fascia dentata, the role of tenascin-C for axonal growth was investigated in vivo. Monoclonal antibodies against the neurite outgrowth and anti-adhesive domains of the molecule were employed. Immunostaining was increased throughout the denervated outer molecular layer by day 2, reached a maximum around day 10, and was back to control levels by four weeks post lesion. Growth cone deflecting as well as neurite outgrowth promoting isoforms of tenascin-C were up-regulated after the lesion. Using electron microscopy, single intensely tenascin-C immunoreactive cells were identified as reactive astrocytes that phagocytose degenerated terminals. In situ hybridization histochemistry for tenascin-C messenger RNA revealed numerous cellular profiles in the denervated outer molecular layer of the ipsilateral and contralateral dentate gyrus two days post lesion. Tenascin-C messenger RNA-positive cells in the outer molecular layer were identified as astrocytes using double-labelling for tenascin-C messenger RNA and glial fibrillary acidic protein immunohistochemistry. Thus, a tenascin-C-rich substrate is present in the outer molecular layer during the time of sprouting and a sharp boundary is formed against the inner molecular layer. This pattern may contribute to the layer-specific sprouting response of surviving afferents after entorhinal lesion. Neurite outgrowth may be promoted within the denervated zone, whereas axons trying to grow into the denervated outer molecular layer, for example from the inner molecular layer, would be deflected by a tenascin-C-rich barrier.

Mapping of a defined neurocan binding site to distinct domains of tenascin-C

Neurocan is a member of the aggrecan family of proteoglycans which are characterized by NH2-terminal domains binding hyaluronan, and COOH-terminal domains containing C-type lectin-like modules. To detect and enhance the affinity for complementary ligands of neurocan, the COOH-terminal neurocan domain was fused with the NH2-terminal region of tenascin-C, which contains the hexamerization domain of this extracellular matrix glycoprotein. The fusion protein was designed to contain the last downstream glycosaminoglycan attachment site and was expressed as a proteoglycan. In ligand overlay blots carried out with brain extracts, it recognized tenascin-C. The interaction was abolished by the addition of EDTA, or TNfn4,5, a bacterially expressed tenascin-C fragment comprising the fourth and fifth fibronectin type III module. The fusion protein directly reacted with this fragment in ligand blot and enzyme-linked immunosorbent assay procedures. Both tenascin-C and TNfn4,5 were retained on Sepharose 4B-linked carboxyl-terminal neurocan domains, which in BIAcore binding studies yielded a KD value of 17 nM for purified tenascin-C. We conclude that a divalent cation-dependent interaction between the COOH-terminal domain of neurocan and those fibronectin type III repeats is substantially involved in the binding of neurocan to tenascin-C.

Effects of tenascin-C in cultured hippocampal astrocytes: NCAM and fibronectin immunoreactivity changes

Tenascin-C is an extracellular matrix glycoprotein with trophic and repulsive properties on neuronal cells, involved in migratory processes of immature neurons. Previous reports demonstrated that this molecule is produced and secreted by astrocytes, in vitro after activation by bFGF or in vivo after CNS lesion. In injured brain the expression of tenascin-C has been correlated with the glial reaction since it was observed in regions suffering a dramatic glial proliferation and hypertrophy. In this report we show that the treatment of cultured hippocampal astrocytes with tenascin-C results in an increased fibronectin and NCAM immunoreactivities. In addition, treated astrocytes form longer extensions than control ones. The number of cells as well as the levels of GFAP mRNA and protein immunoreactivity are not modified after tenascin-C treatment. The present changes may, therefore, be related to the modification of the adhesive properties of astrocytes to the substrate. These observations are compatible with the hypothesis that tenascin-C may contribute to the glial scarring process.

Tenascin-C mRNA and tenascin-C protein immunoreactivity increase in astrocytes after activation by bFGF

Tenascin-C is an extracellular matrix glycoprotein with trophic and repulsive properties, involved in migratory processes in CNS. Previous reports demonstrated that this molecule is produced and secreted by astrocytes. Preliminary data on fibroblasts and astrocytes have suggested that bFGF may modulate tenascin-C expression. bFGF is a mitogenic growth factor, involved in cell differentiation and neovascularization. In the present study, we examined whether bFGF modulates the expression of tenascin-C in hippocampal astrocytes from newborn rats. Our results suggest that bFGF increases the production of tenascin-C by cultured hippocampal astrocytes. We found that both tenascin-C mRNA and protein immunoreactivity were increased after bFGF treatment. Our results also demonstrated that tenascin-C polypeptides were secreted into the extracellular medium. In agreement with previous studies, we suggest that secreted tenascin-C is mainly the high molecular weight form. In addition, our results suggest that a cleavage of the high molecular weight form. In addition, our results suggest that a cleavage of the high molecular weight form may occur in the extracellular medium causing production of proteolytic fragments, that may modify the biological properties of tenascin-C. The present results may be relevant to the understanding of lesion scarring and regeneration process.

Subventricular zone-olfactory bulb migratory pathway in the adult mouse: cellular composition and specificity as determined by heterochronic and heterotopic transplantation

To gain insight into cellular and molecular mechanisms subserving neuronal cell migration in the adult mouse forebrain, we have first investigated the cellular composition of the subventricular zone-olfactory bulb pathway (SVZ-OB). The pathway was essentially composed of cells with neuronal and astrocytic identities, neuronal cells being four times more numerous than astrocytes. Neuronal cells (precursors and some young postmitotic neurons) formed continuous cellular strands of migratory cells from the anterior horn of the lateral ventricle to the olfactory bulb. These chains of migrating cells moved within channels formed by the processes of a special subpopulation of astrocytes. The neuronal cells expressed the embryonic form of polysialic acid neural cell adhesion molecule, and the astrocytes were tenascin-C positive, thus preserving an embryonic cellular environment. Through transplantation experiments, the second part of this study attempted to analyze the functional properties of the adult SVZ-OB pathway. Early postnatal (P2-13) cerebellar progenitor cells, taken from a transgenic mouse line in which cerebellar granule cells and molecular layer interneurons (basket/stellate cells) expressed the reporter gene lacZ, were implanted in the SVZ-OB pathway of adult wild-type mice. Unlike grafted SVZ cells that migrate all along the pathway, none of the cerebellar precursors reached the olfactory bulb, although some of them were able to migrate along the caudal one-third of the pathway. The majority (over 67%) of the migrating cells were progenitors that acquired the phenotype of basket/stellate cells. Granule cell progenitors and most granule cells did not survive transplantation. These results show that the adult SVZ-OB pathway is not a "passive generic guidance" for all classes of premigratory neurons. From the two types of grafted cerebellar progenitors, only those with migratory capability and that do not follow radial glial axes are able to translocate along the SVZ-OB pathway. Furthermore, the basket/stellate cell progenitors are specified at the time of grafting: Neither their identity nor the pace of expression of their major distinctive features are influenced by local signals emanating from the adult forebrain.

Binding of contactin/F11 to the fibronectin type III domains 5 and 6 of tenascin is inhibited by heparin

The structural basis for the interaction between tenascin-C and the neuronal cell adhesion molecule, contactin/F11, was investigated using plasmon surface resonance technology. The binding site on tenascin-C for contactin/F11 is shown to span the two fibronectin type III homology domains 5 and 6. Either domain alone is insufficient for binding. Heparin, heparan sulfate and dermatan sulfate inhibit this interaction through binding to a conserved heparin-binding site on domain 5. In contrast, chondroitin sulfates A and C have no such effect.