Differences in the solubility and susceptibility to proteolytic degradation of basement-membrane components in adult and embryonic mouse tissues

Nidogen-1 expression is associated with overall survival and temozolomide sensitivity in low-grade glioma patients

We investigated the prognostic significance of nidogen-1 (NID1) in glioma. Oncomine, GEPIA, UALCAN, CCGA database analyses showed that NID1 transcript levels were significantly upregulated in multiple cancer types, including gliomas. Quantitative RT-PCR analyses confirmed that NID1 expression was significantly upregulated in glioma tissues compared to paired adjacent normal brain tissue samples (n=9). NID1 silencing enhanced in vitro apoptosis and the temozolomide sensitivity of U251 and U87-MG glioma cells. Protein-protein interaction network analysis using the STRING and GeneMANIA databases showed that NID1 interacts with several extracellular matrix proteins. TIMER database analysis showed that NID1 expression in low-grade gliomas was associated with tumor infiltration of B cells, CD4⁺ and CD8⁺ T cells, macrophages, neutrophils, and dendritic cells. Kaplan-Meier survival curve analysis showed that low-grade gliomas patients with high NID1 expression were associated with shorter overall survival. However, NID1 expression was not associated with overall survival in glioblastoma multiforme patients. These findings demonstrate that NID1 expression in glioma tissues is associated with overall survival of low-grade glioma patients and temozolomide sensitivity. NID1 is thus a potential prognostic biomarker and therapeutic target in low-grade glioma patients.

Reduced vascular basement-membrane immunostaining in mucinous tumours of the ovary

Tumour vasculature is heterogeneous, exhibiting a range of vessel densities and the vascular basement membrane (VBM) of tumour blood vessels may be fragmented or absent. Increased microvessel density (MVD) has been reported in mucinous ovarian tumours as compared with other histologic sub-types. We hypothesized that VBM immunostaining differs between regions of the ovarian tumour vasculature and between ovarian tumour types exhibiting different MVD. Serial sections from 56 ovarian tumours were immunostained using antibodies to the VBM components collagen IV, heparan sulphate proteoglycan and laminin, and the endothelial cell marker CD31. Regions of high and average MVD were selected, and the number of vessels positive for each VBM component were counted and expressed as a percentage of the number of CD31-positive vessels. The percentage of VBM-positive vessels did not differ between the high and average MVD regions of borderline or malignant, mucinous and serous tumours. The percentage of VBM-positive vessels in mucinous tumours was less than that observed in malignant and borderline serous tumours and benign tumours (p < 0.02). Possible explanations for these findings are (i) that VBM turnover is similar throughout the vasculature; (ii) that the VBM is present both during angiogenesis and in the newly formed vessels of high MVD regions; or (iii) that an alternative angiogenesis mechanism is utilized in different ovarian tumour types, or even between different regions of the same tumour.

Characterization of high affinity binding between laminin and the acute-phase protein, serum amyloid A

Serum amyloid A isoforms, apoSAA1 and apoSAA2, are acute-phase proteins of unknown function and can be precursors of amyloid AA peptides (AA) found in animal and human amyloid deposits. These deposits are often a complication of chronic inflammatory disorders and are associated with a local disturbance in basement membrane (BM). In the course of trying to understand the pathogenesis of this disease laminin, a major BM glycoprotein, has been discovered to bind saturably, and with high affinity to murine acute-phase apoSAA. This interaction involves a single class of binding sites, which are ionic in nature, conformation-dependent, and possibly involve sulfhydryls. Binding activity was significantly enhanced by Zn2+, an effect possibly mediated through Cys-rich zinc finger-like sequences on laminin. Collagen type IV also bound apoSAA but with lower affinity. Unexpectedly, no binding was detected for perlecan, a BM proteoglycan previously implicated in AA fibrillogenesis, although a low affinity interaction cannot be excluded. Entactin, another BM protein that functions to cross-link the BM matrix and is normally complexed with laminin, could inhibit laminin-apoSAA binding suggesting apoSAA does not bind to normal BM. Since laminin binds apoSAA with high affinity and has previously been shown to codeposit with AA amyloid fibrils, we postulate that laminin interacts with apoSAA and facilitates nucleation events leading to fibrillogenesis. This work also provides further support for the hypothesis that a disturbance in BM metabolism contributes to the genesis of amyloid. The specificity and avidity of the laminin-apoSAA interaction also implies that it may be a normal event occurring during the inflammatory process, which mediates one or more of the functions recently proposed for apoSAA.

Role of laminin-nidogen complexes in basement membrane formation during embryonic development

Laminin and nidogen (entactin) are major glycoprotein components of basement membranes. At least seven different isoforms of laminin have been identified. Laminin and nidogen form high affinity complexes in basement membranes by specific binding between the laminin gamma 1 chain and the G3 globule of nidogen. Additional interactions between nidogen and collagen IV, perlecan and other basement membrane components result in the formation of ternary complexes between these matrix components. Nidogen is highly susceptible to proteolytic cleavage, and binding to laminin protects nidogen from degradation. Nidogen is considered to have a crucial role as a link protein in the assembly of basement membranes. Basement membrane components are synthesized at high levels during tissue growth and development, and sites of morphogenesis correlate with localized remodelling of basement membranes. The formation of distinct basement membrane matrices in the developing embryo is influenced by the laminin isoforms produced and by whether laminin and nidogen are co-expressed and secreted as a complex or are produced by cooperation between two cell layers. The potential roles of laminin-nidogen complexes, cell-matrix interactions, and other intermolecular interactions within the matrix in basement membrane assembly and stability are discussed in this review.

Synthesis and expression of laminin during human foetal lung development

BACKGROUND

The lung develops by epithelial tubes budding and branching into a flexible mesenchyme. This growth is associated with the remodelling of the epithelial basement membrane, of which laminin is a major component.

METHODS

Both the synthesis and expression of laminin were studied in the human lung between 10 and 31 weeks of gestation, using in situ hybridization and immunohistochemistry.

RESULTS

The synthesis of the beta chain was active in the epithelial and surrounding mesenchymal cells. The mRNAs coding for the gamma chain were less abundant and mainly found in the epithelium. The synthesis of these two chains continued throughout gestation, and no significant difference in the density of hybridization grains could be detected between the tips of the expanding buds and the proximal portions. Immunohistochemical localization of laminin showed important modifications of the basement membrane during gestation. In the first part of the pseudoglandular stage the epithelial basement membrane stained continuously for laminin. Later, the basement membrane was labelled in a graded fashion: at the apex of the growing buds the staining became weak with focal disruptions. Both epithelial and mesenchymal synthesis of laminin remained active, while the polypeptide was undetectable using immunohistochemistry.

CONCLUSIONS

These findings suggest that the remodelling of the basement membrane during human lung morphogenesis is probably not related to a decreasing synthesis of laminin, but to either a proteolytic degradation or the assembly of an inadequate complex undetectable with the polyclonal antibody antilaminin.

Expression of collagen alpha 1(IV), laminin and nidogen genes in the embryonic mouse lung: implications for branching morphogenesis

The patterns of laminin A, B1, B2, nidogen and collagen alpha 1(IV) gene expression in the embryonic mouse lung were determined using in situ hybridization histochemistry at a stage when branching morphogenesis is taking place. Collagen alpha 1(IV), laminin B1 and B2 genes were expressed throughout the mesenchyme and epithelium. Nidogen gene expression was uniform throughout the mesenchyme but was not detected in epithelial cells. Laminin A mRNA was localized to cells closely associated with a basement membrane at the epithelial-mesenchymal interface. However, expression of the laminin A gene was limited to the mesenchymal cells in bronchial regions and to epithelial cells in distal terminal lobules. We propose that the pattern of laminin A gene expression in different regions of the developing lung will influence the structure of the basement membrane at the epithelial-mesenchymal interface and thus have a role in branching morphogenesis.

Effects of the extracellular matrix on fetal choroid plexus epithelial cells: changes in morphology and multicellular organization do not affect gene expression

We have developed a primary culture system for fetal mouse choroid plexus epithelial cells which maintains their differentiated phenotype. When grown on a reconstituted basement membrane substrate (Matrigel) epithelial cells formed aggregates which became embedded in the matrix and developed into characteristic and highly reproducible multicellular vesicular structures. These vesicles consisted of a squamous layer of epithelial cells with extensive attachment to the matrix substrate, surrounding a fluid-filled lumen. Electron microscopy showed that cells comprising these vesicles had a high degree of membrane specialization and polarized morphology which in many respects mimicked the in vivo morphology. Biochemical analyses demonstrated that under these culture conditions the tissue-specific pattern of gene expression of fetal choroid plexus epithelium was maintained. After 6 days in culture these cells contained approximately the same amount of transthyretin mRNA as the 12.5-day choroid plexus in vivo, and the level of total RNA per cell, which is proportional to the protein synthetic capability of the cells, was also maintained. The pattern of protein secretion was also very similar to that generated by fetal mouse choroid plexus cells in vivo. In contrast choroid plexus epithelial cells attached poorly to collagen I gels. Heterogeneous aggregates were formed in which cell-cell interactions were more extensive than cell-substrate interactions, and in no cases was a central lumen observed. Cells on the surface of large aggregates showed some evidence of membrane polarization, while the majority of cells in the cultures exhibited little evidence of polarized morphology. Despite the striking difference in morphology and multicellular organization these cells still expressed high levels of transthyretin mRNA and maintained the same pattern of protein synthesis as cells cultured on Matrigel. These results indicate that the basement membrane is important for the organization of choroid plexus epithelial cells into a functional epithelium in vitro and thus presumably the maintenance of the integrity of the blood-brain barrier in vivo. In contrast to several other epithelial systems which have been studied, the type of extracellular matrix does not appear to directly influence tissue-specific gene expression by choroid plexus epithelial cells. Thus the level of gene expression is not dependent on the cytoarchitecture and multicellular organization of this cell type.

In vitro production of Reichert's membrane by mouse embryo-derived parietal endoderm cell lines

We report the isolation of eight independent cell lines from preimplantation mouse embryos, which have a parietal endoderm phenotype. When grown as aggregates, these cell lines produce large amounts of a basement membrane matrix, that contains laminin, nidogen, heparan sulfate proteoglycan, collagen IV, and BM-40. The biosynthetic profiles of all eight cell lines are very similar to parietal endoderm cells in vivo which synthesize Reichert's membrane. The structure of the matrix produced by the parietal endoderm cell lines (PEC lines) resembles more closely Reichert's membrane than the Engelbreth-Holm-Swarm (EHS) tumor in susceptibility to proteolytic degradation. Since these cell lines produce large quantities of basement membrane they will be useful for structural and functional comparison of a Reichert's membrane matrix with the basement membrane produced by the EHS tumor.