Extracellular Matrix in Neural Plasticity and Regeneration

The extracellular matrix (ECM) is a fundamental component of biological tissues. The ECM in the central nervous system (CNS) is unique in both composition and function. Functions such as learning, memory, synaptogenesis, and plasticity are regulated by numerous ECM molecules. The neural ECM acts as a non-specific physical barrier that modulates neuronal plasticity and axon regeneration. There are two specialized types of ECM in the CNS, diffuse perisynaptic ECM and condensed ECM, which selectively surround the perikaryon and initial part of dendritic trees in subtypes of neurons, forming perineuronal nets. This review presents the current knowledge about the role of important neuronal ECM molecules in maintaining the basic functions of a neuron, including electrogenesis and the ability to form neural circuits. The review mainly focuses on the role of ECM components that participate in the control of key events such as cell survival, axonal growth, and synaptic remodeling. Particular attention is drawn to the numerous molecular partners of the main ECM components. These regulatory molecules are integrated into the cell membrane or disposed into the matrix itself in solid or soluble form. The interaction of the main matrix components with molecular partners seems essential in molecular mechanisms controlling neuronal functions. Special attention is paid to the chondroitin sulfate proteoglycan 4, type 1 transmembrane protein, neural-glial antigen 2 (NG2/CSPG4), whose cleaved extracellular domain is such a molecular partner that it not only acts directly on neural and vascular cells, but also exerts its influence indirectly by binding to resident ECM molecules.

Tenascin-C: Form versus function

Tenascin-C is a large, multimodular, extracellular matrix glycoprotein that exhibits a very restricted pattern of expression but an enormously diverse range of functions. Here, we discuss the importance of deciphering the expression pattern of, and effects mediated by, different forms of this molecule in order to fully understand tenascin-C biology. We focus on both post transcriptional and post translational events such as splicing, glycosylation, assembly into a 3D matrix and proteolytic cleavage, highlighting how these modifications are key to defining tenascin-C function.

Altered gene expression patterns during the initiation and promotion stages of neonatally diethylstilbestrol-induced hyperplasia/dysplasia/neoplasia in the hamster uterus

Neonatal treatment of hamsters with diethylstilbestrol (DES) induces uterine hyperplasia/dysplasia/neoplasia (endometrial adenocarcinoma) in adult animals. We subsequently determined that the neonatal DES exposure event directly and permanently disrupts the developing hamster uterus (initiation stage) so that it responds abnormally when it is stimulated with estrogen in adulthood (promotion stage). To identify candidate molecular elements involved in progression of the disruption/neoplastic process, we performed: (1) immunoblot analyses and (2) microarray profiling (Affymetrix Gene Chip System) on sets of uterine protein and RNA extracts, respectively, and (3) immunohistochemical analysis on uterine sections; all from both initiation stage and promotion stage groups of animals. Here we report that: (1) progression of the neonatal DES-induced hyperplasia/dysplasia/neoplasia phenomenon in the hamster uterus involves a wide spectrum of specific gene expression alterations and (2) the gene products involved and their manner of altered expression differ dramatically during the initiation vs. promotion stages of the phenomenon.

The motile breast cancer phenotype roles of proteoglycans/glycosaminoglycans

The consecutive stages of cancer growth and dissemination are obligatorily perpetrated through specific interactions of the tumor cells with their microenvironment. Importantly, cell-associated and tumor microenvironment glycosaminoglycans (GAGs)/proteoglycan (PG) content and distribution are markedly altered during tumor pathogenesis and progression. GAGs and PGs perform multiple functions in specific stages of the metastatic cascade due to their defined structure and ability to interact with both ligands and receptors regulating cancer pathogenesis. Thus, GAGs/PGs may modulate downstream signaling of key cellular mediators including insulin growth factor receptor (IGFR), epidermal growth factor receptor (EGFR), estrogen receptors (ERs), or Wnt members. In the present review we will focus on breast cancer motility in correlation with their GAG/PG content and critically discuss mechanisms involved. Furthermore, new approaches involving GAGs/PGs as potential prognostic/diagnostic markers or as therapeutic agents for cancer-related pathologies are being proposed.

Matrikines and the lungs

The extracellular matrix is a complex network of fibrous and nonfibrous molecules that not only provide structure to the lung but also interact with and regulate the behaviour of the cells which it surrounds. Recently it has been recognised that components of the extracellular matrix proteins are released, often through the action of endogenous proteases, and these fragments are termed matrikines. Matrikines have biological activities, independent of their role within the extracellular matrix structure, which may play important roles in the lung in health and disease pathology. Integrins are the primary cell surface receptors, characterised to date, which are used by the matrikines to exert their effects on cells. However, evidence is emerging for the need for co-factors and other receptors for the matrikines to exert their effects on cells. The potential for matrikines, and peptides derived from these extracellular matrix protein fragments, as therapeutic agents has recently been recognised. The natural role of these matrikines (including inhibitors of angiogenesis and possibly inflammation) make them ideal targets to mimic as therapies. A number of these peptides have been taken forward into clinical trials. The focus of this review will be to summarise our current understanding of the role, and potential for highly relevant actions, of matrikines in lung health and disease.

Expression of tenascin-C and its isoforms in the breast

Tenascin-C (TNC) is an extracellular matrix glycoprotein which is frequently up-regulated in a variety of pathological conditions including chronic inflammation and cancer. TNC has been implicated in the modulation of cell migration, proliferation, invasion and angiogenesis. Multiple isoforms of TNC can be generated through the alternative splicing of nine exons located in the fibronectin type III region of the molecule. The profile of isoforms expressed differs between cancers and normal breast, with the fully truncated TNC isoform being predominant in normal and benign tissues and higher molecular weight isoforms induced predominantly in cancer. The addition of extra domains within the fibronectin type III repeat domain greatly affects TNC function with multiple exon combinations available for splicing. Exons 14 and 16 are considered to be tumour-associated and have been shown to affect breast cell line invasion and growth in vitro to a greater extent than the full-length TNC isoform. This mini review will provide a summary of the literature to date regarding the expression of TNC isoforms in the breast and also discuss more recent developments in the field regarding exon AD1.

Gene expression analysis of biological systems driving an organotypic model of endometrial carcinogenesis and chemoprevention

An organotypic model of endometrial carcinogenesis and chemoprevention was developed in which normal endometrial organotypic cultures exposed to the carcinogen, DMBA (7,12-dimethylbenz[a]anthracene), developed a cancerous phenotype in the absence, but not presence of subsequent treatment with a flexible heteroarotinoid (Flex-Het), called SHetA2. A discriminant function based on karyometric features of cellular nuclei and an agar clonogenic assay confirmed these histologic changes. Interpretation of microarray data using an internal standard approach identified major pathways associated with carcinogenesis and chemoprevention governed by c-myc, p53, TNFα and Jun genes. Cluster analysis of functional associations of hypervariable genes demonstrated that carcinogenesis is accompanied by a stimulating association between a module of genes that includes tumor necrosis factor α (TNFα), c-myc, and epidermal growth factor-receptor (EGF-R) and a module that includes insulin-like growth factor I-receptor (IGF-IR), p53, and Jun genes. Two secreted proteins involved in these systems, tenascin C and inhibin A, were validated at the protein level. Tenascin C is an EGF-R ligand, and therefore may contribute to the increased EGF-R involvement in carcinogenesis. The known roles of the identified molecular systems in DMBA and endometrial carcinogenesis and chemoprevention supports the validity of this model and the potential clinical utility of SHetA2 in chemoprevention.

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.

High-molecular tenascin-C as an indicator of atypical cells in oral brush biopsies

Tumour-invasion like wound healing is characterised by the formation of an extracellular matrix with a high tenascin-C content. The tenascin-C molecule undergoes alternative splicing. Analysis using antibody BC2 indicates that especially the high-molecular tenascin-C (hm tn-C) variants are typically tumour-associated, while distribution in normal tissue is restrictive. This study investigated whether hm tn-C is a suitable indicator of atypical cells with invasive potential in oral brush biopsies. One hundred fifty nine consecutive oral brush biopsies with histopathological diagnoses were analysed for the identification of atypical cells. A standardised haematoxylin and eosin staining plus standardised immunocytochemistry using the monoclonal anti-hm tn-C antibody was performed. The bound hm tn-C antibodies were detected with the streptavidine/alkaline phosphatase technique in the autostainer. Conventional cytology produced four false-positives when identifying atypical cells in brush biopsies of inflammatory/benign hyperproliferative mucosa (specificity 96%), while 10 in 52 carcinomas and three of eight recurrences were not identified (sensitivity 78%). Ten of these 13 non-identified tumours could be marked when adding the hm tn-C assay (increasing specificity to 99%). Combining the two assays also reduced the false-positive outcomes from four to one (increasing sensitivity to 95%). The positive and negative predictive values were 92 and 88% for conventional cytology vs 98 and 97% for the dual assay. (1) A 95%-sensitivity proves hm tn-C assisted conventional cytology to be a suitable means of identifying atypical cells in oral brush biopsies. (2) The positive (98%) and negative (97%) predictive values obtained approximate hm tn-C assisted conventional cytology to laminin-5 (100/97%).

Differential expression of tenascin-C splicing domains in urothelial carcinomas of the urinary bladder

PURPOSE

Through alternative splicing of the extracellular matrix protein tenascin-C (Tn-C) primary transcript nine type III homology repeats can be independently included or omitted. Large, low spliced Tn-C variants (Tn-C(L)) are preferentially expressed during tissue remodelling processes like tumour invasion to modulate cell migration. The study was aimed to evaluate the differential expression of Tn-C splicing domains in urinary bladder carcinoma with respect to the invasive behaviour.

METHODS

The deposition and synthesis of the Tn-C splicing domains A1-D was analysed in 34 urinary bladder carcinomas by semiquantitative immunohistochemistry using domain specific antibodies and by RT-PCR. Results were correlated to tumour stage and grade.

RESULTS

There is a significant increase of Tn-C(L) with higher tumour stage and grade. Immunohistochemistry revealed a more restricted distribution pattern of A1, B, and/or D domain containing Tn-C variants to invasive tumours, tumour vessels, and to destructed muscle. The mRNA expression patterns of the domains A1-A3 are similar among the different carcinomas. Stronger differences exist in the region from the B to D domain. In general, the domains AD1/C are rarely expressed. AD1 domain expression seems to be connected with compact invasion pattern.

CONCLUSION

In urinary bladder carcinoma a differential expression of Tn-C splicing variants exists in dependence of tumour type, vascularization, and invasive behaviour. Therefore, the detection of different Tn-C splicing domains could be useful for assessment of muscle invasion, tumour surveillance, as well as target structures for antibody based tumour detection and therapy.

Mutual paracrine effects of colorectal tumour cells and stromal cells: modulation of tumour and stromal cell differentiation and extracellular matrix component production in culture

Interactions of tumour and stromal cells influence tumour cell proliferation and differentiation, stromal cell phenotypic transdifferentiation and secretion of extracellular matrix (ECM) components. In this study, we established a monolayer and a three-dimensional cell-to-cell interaction model between canine mammary stromal cells and human colonic carcinoma cell lines (Caco-2 and HT-29) to investigate mutual paracrine effects of tumour cells and stromal cells on (i) tumour cell differentiation, (ii) production of ECM components and (iii) phenotypic transdifferentiation of stromal cells. We showed that when Caco-2 or HT-29 cells are cultured in collagen gels, they form a few small solid cell clusters with no lumina, but when cocultured with stromal cells, the tumour cells formed glandular structures with central lumina. This fibroblast-induced organization and differentiation of Caco-2 cells (not HT-29 cells) appeared to be mediated by transforming growth factor-beta (TGF-beta). Culturing of stromal cells, Caco-2 cells or HT-29 cells alone in both monolayers and gels resulted in weak tenascin-C expression in stromal cells and HT-29 cells and no expression in the Caco-2 cells. Coculturing of stromal cells with tumour cells resulted in increased tenascin-C expression in the stromal cells and HT-29 cells and induced expression of tenascin-C in the Caco-2 cells. This induction and increased expression of tenascin-C appeared to be mediated by TGF-beta. Culturing of stromal cells, Caco-2 cells or HT-29 cells alone on monolayers and in gels resulted in a weak expression of chondroitin sulfate (CS), chondroitin-6-sulfate (C-6-S) and versican in stromal cells and no expression in Caco-2 and HT-29 cells. Coculturing of stromal cells with tumour cells on monolayers and in gels resulted in increased CS, C-6-S and versican expression in stromal cells. This tumour cell-induced expression of CS, C-6-S and versican appeared to be mediated by TGF-beta and platelet-derived growth factor (PDGF). Coculturing of Caco-2 and HT-29 and stromal cells promoted the transdifferentiation of stromal cells into myofibroblasts, and this appeared to be mediated by TGF-beta. These results suggest that TGF-beta and PDGF are part of a paracrine system involved in stromal-epithelial cell interaction important in stromal cell differentiation and ECM component production.

Potential oncogenic action of tenascin-C in tumorigenesis

The prominent expression of tenascin-C in the stroma of most solid tumors, first observed in the mid 1980s, implicates tenascin-C in tumorigenesis. This is also supported by in vitro experiments that demonstrate the capacity of tenascin-C to stimulate tumor growth by various mechanisms including promotion of proliferation, escaping immuno-surveillance and positively influencing angiogenesis. However, tumorigenesis in tenascin-C knock-out mice is not significantly different from that observed in control animals. Perhaps this is not unexpected if one considers that tenascin-C may act as an oncogene. The potential role of tenascin-C in tumorigenesis through its oncogenic action on cellular signaling will be discussed in this review, including how tenascin-C mediated tumor cell detachment might affect genome stability.

Profile of gene expression induced by the tumour promotor TPA in murine epithelial cells

Malignant transformation of mouse skin by chemical carcinogens and tumour promoters, such as the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), is a multistage process that leads to squamous cell carcinoma (SCC) formation. In an effort to identify tumour-associated genes, we studied the influence of short-term TPA-treatment on the gene expression profile of murine skin. A comprehensive microarray with some 5,000 murine gene specific cDNA fragments was established and hybridised with pooled RNA derived from control and TPA-treated dorsal skin samples. Of these genes, 54 were up- and 35 were down-regulated upon TPA application. Additionally, we performed suppression subtractive hybridisation (SSH) with respective RNA pools to generate and analyse a cDNA library enriched for TPA-inducible genes. Expression data of selected genes were confirmed by quantitative real-time PCR and Northern blot analysis. Comparison of microarray and SSH data revealed that 26% of up-regulated genes identified by expression profiling matched with those present in the SSH library. Besides numerous known genes, we identified a large set of unknown cDNAs that represent previously unrecognised TPA-regulated genes in murine skin with potential function in tumour promotion. Additionally, some TPA-induced genes, such as Sprr1A, Saa3, JunB, Il4ralpha, Gp38, RalGDS and Slpi exhibit high basal level in advanced stages of skin carcinogenesis, suggesting that at least a subgroup of the identified TPA-regulated genes may contribute to tumour progression and metastasis.

Tenascin and proteoglycans: the role of tenascin and proteoglycans in canine tumours

Tenascin is a high molecular weight, extracellular matrix glycoprotein, subject to complex spatial and temporal patterns of expression during embryogenesis, wound healing and neoplastic processes. Proteoglycans are complex macromolecules, containing one or more glycosaminoglycans attached to a core protein, which are involved in cell-cell and cell-matrix interaction. Altered expression of both tenascin and proteoglycans has been found in tumours and expression of these two extracellular matrix proteins seems to be modulated in the same way in human and canine tumours. The quantitative and qualitative changes in tenascin and proteoglycan composition may significantly affect behaviour of tumour cells. While tenascin and proteoglycans have many biological functions likely to influence tumour development and progression, their exact role in regulation of tumour cell-cell interaction, proliferation, invasion and metastasis remains to be established. This review focuses on the role of tenascin and proteoglycans in neoplasia and recent developments in canine tumours.

The structure and function of tenascins in the nervous system

The tenascins are a family of large extracellular matrix glycoproteins that comprise five known members. Three of these, tenascin-C (TN-C) tenascin-R (TN-R) and tenascin-Y (TN-Y) are expressed in specific patterns during nervous system development and are down-regulated after maturation. The expression of TN-C, the best studied member of the family, persists in restricted areas of the nervous system that exhibit neuronal plasticity and is reexpressed after lesion. Numerous studies in vitro suggest specific roles for tenascins in the nervous system involving precursor cell migration, axon growth and guidance. TN-C has been shown to occur in a large number of isoform variants generated by combinatorial variation of alternatively spliced fibronectin type III (FNIII) repeats. This finding indicates that TN-C might specify neural microenvironments, a hypothesis supported by recent analysis of TN-C knockout animals, which has begun to reveal subtle nervous system dysfunctions.

A paraxial exclusion zone creates patterned cranial neural crest cell outgrowth adjacent to rhombomeres 3 and 5

Cranial neural crest cell migration is patterned, with neural crest cell-free zones adjacent to rhombomere (R) 3 and R5. These zones have been suggested to result from death of premigratory neural crest cells via upregulation of BMP-4 and Msx-2 in R3 and R5, consequent to R2-, R4-, and R6-derived signals. We reinvestigated this model and found that cell death detected by acridine orange staining in avian embryos varied widely numerically and in pattern, but with a tendency for an elevated zone centered at the R2/3 boundary. In situ hybridization of BMP-4 mRNA resolved to centers at R3 and R5 but Msx-2 resolved to the R2/3 border with only a faint smear from R5 to R6. Outgrowth of neural crest cells was less in isolated R3 cultures than in R1+2, R2, and R4 cultures, but R3 showed neither a decrease in outgrowth of neural crest cells nor an increase in cell death when cocultured with R1+2, R2, or R4. In addition, in serum-free culture, exogenous BMP-4 strikingly reduced neural crest cell outgrowth from R1+2 and R4 as well as R3. Thus we cannot confirm the role of intraneural cell death in patterning rhombomeric neural crest outgrowth. However, grafting quail R2 or R4 adjacent to the chick hindbrain demonstrated a neural crest cell exclusion zone next to R3 and R5. We suggest that one important pattern determinant for rhombomeric neural crest cell migration involves the microenvironment next to the neural tube.