In situ hybridization reveals that type I and III collagens are produced by pericytes in the anterior pituitary gland of rats

Type I and III collagens widely occur in the rat anterior pituitary gland and are the main components of the extracellular matrix (ECM). Although ECM components possibly play an important role in the function of the anterior pituitary gland, little is known about collagen-producing cells. Type I collagen is a heterotrimer of two α1(I) chains (the product of the col1a1 gene) and one α2(I) chain (the product of the col1a2 gene). Type III collagen is a homotrimer of α1(III) chains (the product of the col3a1 gene). We used in situ hybridization with digoxigenin-labeled cRNA probes to examine the expression of col1a1, col1a2, and col3a1 mRNAs in the pituitary gland of adult rats. mRNA expression for these collagen genes was clearly observed, and cells expressing col1a1, col1a2, and col3a1 mRNA were located around capillaries in the gland. We also investigated the possible double-staining of collagen mRNA and pituitary hormones, S-100 protein (a marker of folliculo-stellate cells), or desmin (a marker of pericytes). Col1a1 and col3a1 mRNA were identified in desmin-immunopositive cells. Thus, only pericytes produce type I and III collagens in the rat anterior pituitary gland.     

A Bacillus stearothermophilus Esterase Produced by a Recombinant Bacillus brevis Stabilized by Sulfhydryl Compounds

In the microvascular system, pericytes are located at the abdominal side of capillary endothelial cells.

To discover the role of pericytes in the microvascular system, we have analyzed the extracellular proteins secreted from pericytes isolated from microvessel fragments of rat epididymal fat pads and found that they synthesize substantial amounts of basement membrane components such as type IV collagen and laminins. Secretion of type IV collagen was markedly stimulated by ascorbic acid phosphate. Reducing and non-reducing sodium dodecyl sulfate gel electrophoresis showed that pericytes produce six laminin chains assembled into different trimeric isoforms. Two of them were similar to laminin variants produced by aortic and pulmonal endothelial cells but others were suggested to be novel variants.     

Ontogenesis of the murine hepatic extracellular matrix: an immunohistochemical study

To define the role of the extracellular matrix (ECM) in hepatogenesis, we examined the temporal and spatial deposition of fibronectin, laminin and collagen types I and IV in 12.5-21.5 day fetal and 1, 7 and 14 day postnatal rat livers. In early fetal liver, discontinuous deposits of the four ECM components studied were present in the perisinusoidal space, with laminin being the most prevalent. All basement membrane zones contained collagen type IV and laminin, including those of the capsule (mesothelial), portal vein radicles and bile ductules. Fibronectin had a distribution similar to that of collagen type IV early in gestation. However, at later gestational dates, fibronectin distribution in the portal triads approached that of collagen type I, being present in the interstitial connective tissues; whereas, collagen type IV and laminin were restricted to vascular and biliary basement membrane zones in those regions. The cytoplasm of some sinusoidal lining cells and hepatocytes reacted with antibodies to extracellular matrix components. By electron microscopy the immunoreactive material was localized in the endoplasmic reticulum, indicating the ability of these cells to synthesize these ECM proteins. Biliary ductular cells had prominent intracytoplasmic staining for laminin and collagen type IV from day 19.5 gestation until 7 days of postnatal life, but lacked demonstrable fibronectin or collagen type I. These results demonstrate that by 12.5 days of gestation the rat liver anlage has deposited a complex extracellular matrix in the perisinusoidal space. The prevalence of laminin in the developing hepatic lobules suggests a possible role for this glycoprotein in hepatic morphogenesis. In view of the intimate association of the hepatic lobular extracellular matrix with the developing vasculature, we hypothesize that laminin provides a scaffold of the developing liver, but once the ontogenesis is complete, intrahepatic perisinusoidal laminin expression is suppressed.     

Cooperativity between Sertoli cells and testicular peritubular cells in the production and deposition of extracellular matrix components

We examined the synthesis and deposition of extracellular matrix (ECM) components in cultures of Sertoli cells and testicular peritubular cells maintained alone or in contact with each other. Levels of soluble ECM components produced by populations of isolated Sertoli cells and testicular peritubular cells were determined quantitatively by competitive enzyme-linked immunoabsorbent assays, using antibodies shown to react specifically with Type I collagen, Type IV collagen, laminin, or fibronectin. Peritubular cells in monoculture released into the medium fibronectin (432 to 560 ng/microgram cell DNA per 48 h), Type I collagen (223 to 276 ng/microgram cell DNA per 48 h), and Type IV collagen (350 to 436 ng/microgram cell DNA per 48 h) during the initial six days of culture in serum-free medium. In contrast, Sertoli cells in monoculture released into the medium Type IV collagen (322 to 419 ng/microgram cell DNA per 48 h) but did not form detectable amounts of Type I collagen or fibronectin during the initial six days of culture. Neither cell type produced detectable quantities of soluble laminin. Immunocytochemical localization investigations demonstrated that peritubular cells in monoculture were positive for fibronectin, Type I collagen, and Type IV collagen but negative for laminin. In all monocultures most of the ECM components were intracellular, with scant deposition as extracellular fibrils. Sertoli cells were positive immunocytochemically for Type IV collagen and laminin but negative for fibronectin and Type I collagen. Co-cultures of peritubular cells and Sertoli cells resulted in interactions that quantitatively altered levels of soluble ECM components present in the medium. This was correlated with an increased deposition of ECM components in extracellular fibrils. The data correlated with an increased deposition of ECM components in extracellular fibrils. The data presented here we interpret to indicate that the two cell types in co-culture act cooperatively in the formation and deposition of ECM components. Results are discussed with respect to the nature of interactions between mesenchymal peritubular cell precursors and adjacent epithelial Sertoli cell precursors in the formation of the basal lamina of the seminiferous tubule.     

Extracellular matrix protein mediated regulation of the osteoblast differentiation of bone marrow derived human mesenchymal stem cells

The biomimetic approach of tissue engineering exploits the favorable properties of the extracellular matrix (ECM), to achieve better scaffold performance and tissue regeneration. ECM proteins regulate cell adhesion and differentiation through integrin mediated signal transduction. In the present study, we have examined the role of ECM proteins such as collagen type I, fibronectin, laminin and vitronectin in regulating the proliferation and osteogenic differentiation of bone marrow derived human mesenchymal stem cells (hMSCs). hMSCs were grown on selected ECM protein treated tissue culture plates. The growth kinetics was assessed by calculating the doubling time of the cells on different ECM treated plates. The cells were directed to osteoblast lineage by growing them in osteogenic induction media for 21 day. Differentiation was evaluated at different time points by osteoblast differentiation associated gene expression, alkaline phosphatase (ALP) activity, histochemical staining for mineralized matrix and calcium quantification. The doubling time of hMSCs cultured on collagen type I was significantly low, which was followed by laminin and fibronectin treated plates. However, doubling time of hMSCs cultured on vitronectin treated plate was not significantly different than that of the untreated control. High ALP gene (ALPL) expression and associated enhancement of mineralization were observed on collagen type I, fibronectin and vitronectin treated plates. Collagen type I showed early onset of mineralization with high ALP activity and up-regulation of osteopontin, ALPL, bone sialoprotein and osteocalcin genes. Vitronectin also up-regulated these genes and showed the highest amount of calcium in the secreted mineral matrix. Therefore, we conclude that, ECM proteins indeed modified the growth patterns and induced the osteoblast differentiation of hMSCs. Our findings have significant implication for bone tissue engineering applications.     

Binding of extracellular matrix proteins to Paracoccidioides brasiliensis

Adhesion to extracellular matrix (ECM) proteins plays a crucial role in invasive fungal diseases. ECM proteins bind to the surface of Paracoccidioides brasiliensis yeast cells in distinct qualitative patterns. Extracts from Pb18 strain, before (18a) and after animal inoculation (18b), exhibited differential adhesion to ECM components. Pb18b extract had a higher capacity for binding to ECM components than Pb18a. Laminin was the most adherent component for both samples, followed by type I collagen, fibronectin, and type IV collagen for Pb18b. A remarkable difference was seen in the interaction of the two extracts with fibronectin and their fragments. Pb18b extract interacted significantly with the 120-kDa fragment. Ligand affinity binding assays showed that type I collagen recognized two components (47 and 80kDa) and gp43 bound both fibronectin and laminin. The peptide 1 (NLGRDAKRHL) from gp43, with several positively charged amino acids, contributed most to the adhesion of P. brasiliensis to Vero cells. Synthetic peptides derived from peptide YIGRS of laminin or from RGD of both laminin and fibronectin showed the greatest inhibition of adhesion of gp43 to Vero cells. In conclusion, this work provided new molecular details on the interaction between P. brasiliensis and ECM components.     

Vasculogenic and angiogenic potential of adipose stromal vascular fraction cell populations in vitro

Adipose-derived stromal vascular fraction (SVF) is a heterogeneous cell source that contains endothelial cells, pericytes, smooth muscle cells, stem cells, and other accessory immune and stromal cells. The SVF cell population has been shown to support vasculogenesis in vitro as well vascular maturation in vivo. Matrigel, an extracellular matrix (ECM) mixture has been utilized in vitro to evaluate tube formation of purified endothelial cell systems. We have developed an in vitro system that utilizes freshly isolated SVF and ECM molecules both in pure form (fibrin, laminin, collagen) as well as premixed form (Matrigel) to evaluate endothelial tip cell formation, endothelial stalk elongation, and early stages of branching and inosculation. Freshly isolated SVF rat demonstrate cell aggregation and clustering (presumptive vasculogenesis) on Matrigel ECM within the first 36 h of seeding followed by tip cell formation, stalk cell formation, branching, and inosculation (presumptive angiogenesis) during the subsequent 4 days of culture. Purified ECM molecules (laminin, fibrin, and collagen) promote cell proliferation but do not recapitulate events seen on Matrigel. We have created an in vitro system that provides a functional assay to study the mechanisms of vasculogenesis and angiogenesis in freshly isolated SVF to characterize SVF’s blood vessel forming potential prior to clinical implantation.     

Biosynthesis and deposition of a noncovalent laminin-heparan sulfate proteoglycan complex and other basal lamina components by a human malignant cell line

The basal lamina components laminin, heparan sulfate proteoglycan (HSPG), and type IV collagen were synthesized and codeposited in the extracellular matrix (ECM) by a cultured human cell line from gestational choriocarcinoma (JAR). Laminin and HSPG formed a noncovalent complex detected by the coimmunoprecipitation of HSPG with laminin from cell lysates and culture media. The complex was stable in the cell lysis buffer that contained detergents (1% Triton X-100, 0.5% deoxycholate, and 0.1% sodium dodecyl sulfate) and sodium chloride (from 0.15 to 1.0 M), but was dissociated by adding 8 M urea to the detergent lysates. Even though JAR cells produced roughly equal amounts of HSPG and chondroitin sulfate proteoglycan, only HSPG complexed with laminin, suggesting a specific interaction between these basal lamina components. The laminin-HSPG complex was deposited and retained in the ECM. This was shown biochemically by isolating an enriched fraction of ECM from JAR cells cultured on native type I collagen gels. At steady state, more than half (52%) of the laminin-HSPG in the culture was recovered in the ECM fraction, in contrast to 16% of the total laminin and 29% of the total type IV collagen, which were secreted to a greater extent than laminin-HSPG into the culture medium. The retention of the laminin-HSPG complex in the ECM suggests that it may participate in the assembly of the basal lamina-like extracellular matrix deposited by JAR cultures. Omission of ascorbate from the culture medium abolished the ECM deposition of type IV collagen but had little effect on the deposition of laminin or laminin-HSPG. This demonstrates that the stable deposition of laminin-HSPG and laminin in the collagen-based choriocarcinoma cultures is not dependent on an assembled network of type IV collagen.     

Avian vasculogenesis and the distribution of collagens I, IV, laminin, and fibronectin in the heart primordia

The heart-forming regions of the early embryo are composed of splanchnic mesoderm, endoderm, and the associated ECM. The ECM of the heart-forming regions in stage 7-9 chicken embryos was examined using immunofluorescence. Affinity purified antibodies to chicken collagens type I and IV, chicken fibronectin, and mouse laminin were used as probes. We report that (1) the basement membrane of the endoderm contains immunoreactive laminin and collagen IV; (2) the nascent basement membrane of the heart splanchnic mesoderm contains immunoreactive laminin, but not type IV collagen, and (3) the prominent ECM between the splanchnic mesoderm and the endoderm (the primitive-heart ECM) contains collagen IV, collagen I, fibronectin, but not laminin. In addition, we describe microscopic observations on the spatial relationship of cardiogenic cells to the primitive-heart ECM and the endodermal basement membrane.     

Binding of Streptococcus mutans to extracellular matrix molecules and fibrinogen

We have determined the ability of Streptococcus mutans cells to bind to extracellular matrix (ECM) molecules and fibrinogen. S. mutans cells were found to bind fibronectin, laminin, collagen type I, and fibrinogen. An isogenic S. mutans strain with a defect in the expression of the major surface protein of S. mutans, antigen I/II, possessed a reduced ability to bind fibronectin, collagen, and fibrinogen but not laminin, suggesting that antigen I/II contributes during pathological processes to the interaction of S. mutans cells with fibronectin, collagen type I, and fibrinogen.     

Invasive growth and topoisomerase-switch induced by tumorous extracellular matrix in osteosarcoma cell culture

Osteosarcoma cells are capable of extracellular matrix (ECM) synthesis. The ability of ECM to trigger the proliferation of a novel osteosarcoma cell line (OSCORT) was tested in this study in relation to a known tumor ECM, isolated from Engelbreth-Holm-Swarm (EHS) sarcoma (EHS-ECM). OSCORT was grown in monolayer, in EHS-ECM and in ECM deposited by the cells (OSCORT-ECM). Both EHS-ECM and OSCORT-ECM increased the proliferation and migration of OSCORT cells. Among the ECM biopolymers, heparan sulfate proteoglycan (HSPG) and fibronectin enhanced invasive growth, collagen type IV reduced it, while laminin had no effect. Among the ECM components HSPG and collagen IV increased both the synthesis and activation of collagenase type IV, and all the ECM components substantially increased beta1 integrin levels in the cells. The majority of ECM biopolymers decreased the level of topoisomerase I (except laminin) and elevated topoisomerase II (except fibronectin) in OSCORT. The switch in the ratio between the activities of topoisomerases I and II was mainly due to HSPG. The HSPG synthesized by OSCORT cells is described as agrin, which is a novel finding. The present study showed that HSPG (agrin) showed the most remarkable stimulatory action on the growth and migration of OSCORT cells. HSPG-induced topoisomerase II-induction deserves further experimentation, to discover its relevance to tumor progression.     

Abnormal mucosal extracellular matrix deposition is associated with increased TGF-beta receptor-expressing mesenchymal cells in a mouse model of colitis.

Transforming growth factor-beta (TGF-beta) depresses mucosal inflammation and upregulates extracellular matrix (ECM) deposition. We analyzed TGF-beta receptors RI and RII as well as ECM components using the CD4(+) T-cell-transplanted SCID mouse model of colitis. The principal change in colitis was an increased proportion of TGF-beta RII(+) mucosal mesenchymal cells, predominantly alpha-smooth muscle actin (SMA)(+) myofibroblasts, co-expressing vimentin and basement membrane proteins, but not type I collagen. TGF-beta RII(+) SMA(-) fibroblasts producing type I collagen were also increased, particularly in areas of infiltration and in ulcers. Type IV collagen and laminin were distributed throughout the gut lamina propria in disease but were restricted to the basement membrane in controls. In areas of severe epithelial damage, type IV collagen was lost and increased type I collagen was observed. To examine ECM production by these cells, mucosal mesenchymal cells were isolated. Cultured cells exhibited a similar phenotype and matrix profile to those of in vivo cells. The data suggested that there were at least two populations of mesenchymal cells responsible for ECM synthesis in the mucosa and that ligation of TGF-beta receptors on these cells resulted in the disordered and increased ECM production observed in colitic mucosa.     

Involvement of metalloprotease-2 in the development of human brain microvessels

The involvement of the metalloprotease-2 (MMP-2) in vessel development was investigated in the human telencephalon by double immunoreactions with antibodies to the enzyme, latent (proMMP-2) and active (aMMP-2) forms, and an antibody against collagen type IV, a constitutive component of the extracellular matrix (ECM) of the vessel basal lamina. MMP-2 is expressed in both 12- and 18-week telencephalic vessels, the proenzyme being mainly localised in endothelial cells and the active form prevailing in -actin-reactive periendothelial cells identified as pericytes. Endothelial cells intensely positive for aMMP-2 were revealed in some microvessels and appeared locally associated with discontinuities of the collagen basal lamina. No detectable expression of MMP-2 was observed in perivascular glial processes revealed by vimentin/glial fibrillary acidic protein immunostainings. Double immunoreactions performed to further investigate telencephalon angiogenesis have demonstrated that both the endothelial cells and pericytes strongly express vascular endothelial growth factor (VEGF). Taken together, the results indicate that MMP-2 is largely involved in human brain angiogenesis and suggest that endothelial cells and pericytes tightly interplay in both angiogenesis mechanisms, by ECM proteolysis, and angiogenesis regulation, by local (autocrine/juxtacrine) VEGF action.Francesco Girolamo and Daniela Virgintino contributed equally to this work     

Expression and adhesive properties of basement membrane proteins in cerebral capillary endothelial cell cultures

Previous studies have indicated the importance of basement membrane components both for cellular differentiation in general and for the barrier properties of cerebral microvascular endothelial cells in particular. Therefore, we have examined the expression of basement membrane proteins in primary capillary endothelial cell cultures from adult porcine brain. By indirect immunofluorescence, we could detect type IV collagen, fibronectin, and laminin both in vivo (basal lamina of cerebral capillaries) and in vitro (primary culture of cerebral capillary endothelial cells). In culture, these proteins were secreted at the subcellular matrix. Moreover, the interaction between basement membrane constituents and cerebral capillary endothelial cells was studied in adhesion assays. Type IV collagen, fibronectin, and laminin proved to be good adhesive substrata for these cells. Although the number of adherent cells did not differ significantly between the individual proteins, spreading on fibronectin was more pronounced than on type IV collagen or laminin. Our results suggest that type IV collagen, fibronectin, and laminin are not only major components of the cerebral microvascular basal lamina, but also assemble into a protein network, which resembles basement membrane, in cerebral capillary endothelial cell cultures.     

The leukocyte-endothelial cell interactions are modulated by extracellular matrix proteins.

BACKGROUND: Endothelium is supported, in normal conditions, by a basement membrane composed, among others, by collagen IV and laminin. Changes in the basement membrane composition could induce changes in endothelial cell modifying their interactions with leukocytes. METHODS AND RESULTS: Isolated polymorphonuclear cells (PMN) and peripheral blood mononuclear cells (PBMC) were added to cultured human umbilical endothelial cells (HuVEC) previously seeded on collagen IV, collagen I or gelatin. Adhesion of leukocytes to HUVEC and specific cytotoxicity were analysed. PMN adhesion and cytotoxicity were lower whereas those from PBMC were higher when HuVEC were seeded on collagen I, as compared with cells seeded on collagen IV. To analyse the mechanisms involved in these phenomena, P-selectin, ICAM-1, VCAM-1 and MCP- 1 expression were evaluated in HuVEC seeded on the different ECM components. P-selectin and mRNA expression of VCAM-1 were lower in cells seeded on collagen I. By contrast, MCP-1 expression was higher in collagen I. Collagen I-dependent effects were partially prevented when collagen I was treated with pepsin. ILK activity was lower in cells seeded on collagen I, whereas ERK 1/2 activity was enhanced. ILK overexpression reduced ERK 1/2 phosphorylation and this could promote the reduction in P-selectin and the increase in MCP-1. CONCLUSION: Collagen I decreased ILK activity and this would induce an increase in ERK 1/2 activity in HuVEC. As a consequence, the P-selectin content is diminished and, by contrast, the MCP-1 content is increased. The final effect is a lower recruitment of PMN and a higher adhesion of PBMC.     

Type XVII collagen (BP180) can function as a cell−matrix adhesion molecule via binding to laminin 332

Collagen XVII (COL17) is a transmembrane glycoprotein that is expressed on the basal surface of basal epidermal keratinocytes. Previous observations have led to the hypothesis that an interaction between COL17 and laminin 332, an extracellular matrix protein, contributes to the attachment of the basal keratinocyte to the basement membrane. In order to isolate and manipulate COL17 interactions with ECM components, we induced COL17 expression in two cells lines, SK-MEL1 and K562, that exhibit little or no capacity to attach to our test substrates, including laminin 332, types I and IV collagen, and fibronectin. Cells expressing high levels of COL17 preferentially adhered to a laminin 332 matrix, and, to a lesser extent, type IV collagen, while showing little or no binding to type I collagen or fibronectin. A quantitative analysis of cell adhesive forces revealed that, compared with COL17-negative cells, COL17-positive cells required over 7-fold greater force to achieve 50% detachment from a laminin 332 substrate. When a cell preparation (either K562 or SK-MEL1) with heterogeneous COL17 expression levels was allowed to attach to a laminin 332 matrix, the COL17-positive and COL17-negative cells differentially sorted to the bound and unbound cell fractions, respectively. COL17-dependent attachment to laminin 332 could be reduced or abolished by siRNA-mediated knock-down of COL17 expression or by adding to the assay wells specific antibodies against COL17 or laminin 332. These findings provide strong support for the hypothesis that cell surface COL17 can interact with laminin 332 and, together, participate in the adherence of a cell to the extracellular matrix.     

Revealing non-genetic adhesive variations in clonal populations by comparative single-cell force spectroscopy

Cell populations often display heterogeneous behavior, including cell-to-cell variations in morphology, adhesion and spreading. However, better understanding the significance of such cell variations for the function of the population as a whole requires quantitative single-cell assays. To investigate adhesion variability in a CHO cell population in detail, we measured integrin-mediated adhesion to laminin and collagen, two ubiquitous ECM components, by AFM-based single-cell force spectroscopy (SCFS). CHO cells generally adhered more strongly to laminin than collagen but population adhesion force distributions to both ECM components were broad and partially overlapped. To determine the levels of laminin and collagen binding in individual cells directly, we alternatingly measured single cells on adjacent microstripes of collagen and laminin arrayed on the same adhesion substrate. In repeated measurements (≥60) individual cells showed a stable and ECM type-specific adhesion response. All tested cells bound laminin more strongly, but the scale of laminin over collagen binding varied between cells. Together, this demonstrates that adhesion levels to different ECM components are tightly yet differently set in each cell of the population. Adhesion variability to laminin was non-genetic and cell cycle-independent but scaled with the range of α6 integrin expression on the cell surface. Adhesive cell-to-cell variations due to varying receptor expression levels thus appear to be an inherent feature of cell populations and should to be considered when fully characterizing population adhesion. In this approach, SCFS performed on multifunctional adhesion substrates can provide quantitative single-cell information not obtainable from population-averaging measurements on homogeneous adhesion substrates.     

Cranial and trunk neural crest cells use different mechanisms for attachment to extracellular matrices.

We have used a quantitative cell attachment assay to compare the interactions of cranial and trunk neural crest cells with the extracellular matrix (ECM) molecules fibronectin, laminin and collagen types I and IV. Antibodies to the beta 1 subunit of integrin inhibited attachment under all conditions tested, suggesting that integrins mediate neural crest cell interactions with these ECM molecules. The HNK-1 antibody against a surface carbohydrate epitope under certain conditions inhibited both cranial and trunk neural crest cell attachment to laminin, but not to fibronectin. An antiserum to alpha 1 intergrin inhibited attachment of trunk, but not cranial, neural crest cells to laminin and collagen type I, though interactions with fibronectin or collagen type IV were unaffected. The surface properties of trunk and cranial neural crest cells differed in several ways. First, trunk neural crest cells attached to collagen types I and IV, but cranial neural crest cells did not. Second, their divalent cation requirements for attachment to ECM molecules differed. For fibronectin substrata, trunk neural crest cells required divalent cations for attachment, whereas cranial neural crest cells bound in the absence of divalent cations. However, cranial neural crest cells lost this cation-independent attachment after a few days of culture. For laminin substrata, trunk cells used two integrins, one divalent cation-dependent and the other divalent cation-independent (Lallier, T. E. and Bronner-Fraser, M. (1991) Development 113, 1069-1081). In contrast, cranial neural crest cells attached to laminin using a single, divalent cation-dependent receptor system. Immunoprecipitations and immunoblots of surface labelled neural crest cells with HNK-1, alpha 1 integrin and beta 1 integrin antibodies suggest that cranial and trunk neural crest cells possess biochemically distinct integrins. Our results demonstrate that cranial and trunk cells differ in their mechanisms of adhesion to selected ECM components, suggesting that they are non-overlapping populations of cells with regard to their adhesive properties.