Histochemical demonstration of collagen fibers in ascorbic-acid-fed cell cultures

Curved adhesions mediate cell attachment to soft matrix fibres in three dimensions

Integrin-mediated focal adhesions are the primary architectures that transmit forces between the extracellular matrix (ECM) and the actin cytoskeleton. Although focal adhesions are abundant on rigid and flat substrates that support high mechanical tensions, they are sparse in soft three-dimensional (3D) environments. Here we report curvature-dependent integrin-mediated adhesions called curved adhesions. Their formation is regulated by the membrane curvatures imposed by the topography of ECM protein fibres. Curved adhesions are mediated by integrin ɑvβ5 and are molecularly distinct from focal adhesions and clathrin lattices. The molecular mechanism involves a previously unknown interaction between integrin β5 and a curvature-sensing protein, FCHo2. We find that curved adhesions are prevalent in physiological conditions, and disruption of curved adhesions inhibits the migration of some cancer cell lines in 3D fibre matrices. These findings provide a mechanism for cell anchorage to natural protein fibres and suggest that curved adhesions may serve as a potential therapeutic target.

Curved adhesions mediate cell attachment to soft matrix fibres in 3D

Mammalian cells adhere to the extracellular matrix (ECM) and sense mechanical cues through integrin-mediated adhesions 1, 2 . Focal adhesions and related structures are the primary architectures that transmit forces between the ECM and the actin cytoskeleton. Although focal adhesions are abundant when cells are cultured on rigid substrates, they are sparse in soft environments that cannot support high mechanical tensions 3 . Here, we report a new class of integrin-mediated adhesions, curved adhesions, whose formation is regulated by membrane curvature instead of mechanical tension. In soft matrices made of protein fibres, curved adhesions are induced by membrane curvatures imposed by the fibre geometry. Curved adhesions are mediated by integrin ɑVβ5 and are molecularly distinct from focal adhesions and clathrin lattices. The molecular mechanism involves a previously unknown interaction between integrin β5 and a curvature-sensing protein FCHo2. We find that curved adhesions are prevalent in physiologically relevant environments. Disruption of curved adhesions by knocking down integrin β5 or FCHo2 abolishes the migration of multiple cancer cell lines in 3D matrices. These findings provide a mechanism of cell anchorage to natural protein fibres that are too soft to support the formation of focal adhesions. Given their functional importance for 3D cell migration, curved adhesions may serve as a therapeutic target for future development.

Pancreatic islet basement membrane loss and remodeling after mouse islet isolation and transplantation: impact for allograft rejection

The isolation of islets by collagenase digestion can cause damage and impact the efficiency of islet engraftment and function. In this study, we assessed the basement membranes (BMs) of mouse pancreatic islets as a molecular biomarker for islet integrity, damage after isolation, and islet repair in vitro as well as in the absence or presence of an immune response after transplantation. Immunofluorescence staining of BM matrix proteins and the endothelial cell marker platelet endothelial cell adhesion molecule-1 (PECAM-1) was performed on pancreatic islets in situ, isolated islets, islets cultured for 4 days, and islet grafts at 3-10 days posttransplantation. Flow cytometry was used to investigate the expression of BM matrix proteins in isolated islet β-cells. The islet BM, consisting of collagen type IV and components of Engelbreth-Holm-Swarm (EHS) tumor laminin 111, laminin α2, nidogen-2, and perlecan in pancreatic islets in situ, was completely lost during islet isolation. It was not reestablished during culture for 4 days. Peri- and intraislet BM restoration was identified after islet isotransplantation and coincided with the migration pattern of PECAM-1(+) vascular endothelial cells (VECs). After islet allotransplantation, the restoration of VEC-derived peri-islet BMs was initiated but did not lead to the formation of the intraislet vasculature. Instead, an abnormally enlarged peri-islet vasculature developed, coinciding with islet allograft rejection. The islet BM is a sensitive biomarker of islet damage resulting from enzymatic isolation and of islet repair after transplantation. After transplantation, remodeling of both peri- and intraislet BMs restores β-cell-matrix attachment, a recognized requirement for β-cell survival, for isografts but not for allografts. Preventing isolation-induced islet BM damage would be expected to preserve the intrinsic barrier function of islet BMs, thereby influencing both the effector mechanisms required for allograft rejection and the antirejection strategies needed for allograft survival.

Tissue transglutaminase is the target in both rodent and primate tissues for celiac disease-specific autoantibodies

BACKGROUND

Endomysial antibodies have recently been shown to react with tissue transglutaminase. This study was undertaken to investigate whether the tissue distribution of transglutaminase is also compatible with reticulin, jejunal, and fibroblast autoantibody binding patterns.

METHODS

Sera from patients with and without celiac disease, monoclonal tissue transglutaminase antibodies, and sera from mice parenterally immunized against commercially available tissue transglutaminase, transglutaminase complexed with gliadin, or gliadin were used in indirect immunofluorescence and double-staining studies using both rodent and primate tissues as substrates. Also, antibody competition, affinity chromatography, and potassium thiocyanate extraction studies were undertaken.

RESULTS

Tissue transglutaminase antibody binding patterns were identical with the extracellular binding patterns seen with celiac patient sera. Human umbilical cord-derived fibroblasts exhibited both cytoplasmic and extracellular matrix staining. Double staining with patients' sera and tissue transglutaminase antibodies showed complete overlapping. Tissue transglutaminase effectively absorbed reticulin-endomysial antibodies from celiac sera, and patients' sera blocked the staining of the monoclonal tissue transglutaminase antibodies. Potassium thiocyanate extraction abolished the staining patterns, but they were elicited again after readdition of tissue transglutaminase.

CONCLUSIONS

Reticulin, endomysial, and jejunal antibodies detect transglutaminase in both rodent and primate tissues, indicating that these tissue autoantibodies are identical.

Autoantibodies in celiac disease: importance of fibroblasts

BACKGROUND

Serum reticulin and endomysium autoantibodies are highly celiac disease-specific, and the autoantigens have been shown to be derived from human fibroblasts. Among human tissues, the umbilical cord also expresses these antigens. This study was conducted to compare different autoantibody tests and especially to elucidate whether human umbilical cord is a suitable substrate in tests and whether the cord jelly-derived fibroblasts express the antigens.

METHODS

The indirect immunofluorescence method was used to detect the tissue and Wharton's jelly-derived fibroblast antibodies in 334 celiac disease and control sera samples. Affinity chromatography studies were used to show the correlation between human fibroblast-derived autoantigens and tissue and gliadin antibodies. The jelly-derived fibroblasts were used as antigen in a whole-cell enzyme-linked immunosorbent assay.

RESULTS

Celiac disease patient sera showed IgA-class human umbilical cord antibody with high sensitivity (100%) and specificity (99%). All celiac disease patient sera tested showed in indirect immunofluorescence the molecules expressed by Wharton's jelly-derived fibroblasts. The whole-cell fibroblast autoantibody enzyme-linked immunosorbent assay had a sensitivity of 100% and a specificity of 81%. Human fibroblast-derived celiac disease autoantigens absorbed most of the IgA responsible for human umbilical cord antibodies but not the IgA responsible for gliadin antibodies in the same sera.

CONCLUSIONS

Wharton's jelly-derived fibroblast autoantibodies tested in a novel whole-cell enzyme-linked immunosorbent assay correlated well with the human umbilical cord but not with gliadin antibodies.

Development of a cell line from skin of goldfish, Carassius auratus, and effects of ascorbic acid on collagen deposition

Growth characteristics and collagen expression were investigated in GFSk-S1, a cell line derived from the skin of an adult goldfish (Carassius auratus). These cells are anchorage dependent, grow well in Leibovitz-15 medium with 10% fetal bovine serum, and have been subcultured routinely for 5 years. Cells at various passages have been successfully cryopreserved and thawed. GFSk-S1 cells show mainly a fibroblastic morphology at low density, but at confluence islands of epithelial-shaped cells appear among the fibroblastic cells. The cells require little maintenance, and cultures have been kept viable for more than 3 months without medium changes. Although best growth was observed at room temperature, cell proliferation still occurred at 28 degrees C, and a subline was maintained and passaged for over a year at 25 degrees C. Cells were exposed to various concentrations of ascorbic acid, and its effects on collagen secretion were monitored by light and electron microscopy. Under phase-contrast microscopy, confluent GFSk-S1 cells exposed to ascorbic acid at 50 micrograms/ml showed distinct development of fibres as early as 3 days after treatment. Histochemical staining for collagen demonstrated a thick network of fibres under a monolayer of ascorbic acid-treated GFSk-S1 cells, and observation by transmission electron microscopy showed collagen fibres with typical banding pattern. This cell line appears to show a stable genotype, as collagen expression was induced at all passages. GFSk-S1 could be useful for studies not only of regulation of protein synthesis, but also of cell differentiation and wound healing.

Products of cells from gliomas: IX. Evidence that two fundamentally different mechanisms change extracellular matrix expression by gliomas

Four human astrocytic gliomas of high grade of malignancy were each evaluated in tissue and in vitro for percentages of cells expressing glial fibrillary acidic protein (GFAP), collagen type IV, laminin and fibronectin assessed by immunofluorescence with counterstaining of nuclear DNA. Percentages of cells with reticulin and cells binding fluorescein-labeled Ulex europaeus agglutinin were also assessed. In tissue, each extracellular matrix (ECM) component was associated with cells in the walls of abnormal proliferations of glioma vessels, and all four tumors had the same staining pattern. Two strikingly different patterns of conversion of gene product expression emerged during in vitro cultivation. (1). In the most common pattern, percentages of all six markers consistently shifted toward the exact phenotype of mesenchymal cells in abnormal vascular proliferations: increased reticulin, collagen type IV, laminin and fibronectin; markedly decreased glial marker GFAP and absent endothelial marker Ulex europaeus agglutinin. The simplest explanation of this constellation of changes coordinated toward expression of vascular ECM markers is that primary glioma cell cultures are overgrown by mesenchymal cells from the abnormal vascular proliferations of the original glioma. These cell cultures were tested for in situ hybridization (ISH) signals of chromosomes 7 and 10. Cells from one glioma had diploid signals. Cells from the other glioma had aneuploid signals indicating they were neoplastic; however, their signals reflected different numerical chromosomal aberrations than those common to neoplastic glia. (2). The second pattern was different. Cells with ISH chromosomal signals of neoplastic glia retained GFAP, and gained collagen type IV. Their laminin and fibronectin diminished, but persisted among a lower percentage of cells. Cloning and double immunofluorescence confirmed the presence of individual cells with glial and mesenchymal markers. A cell expressing GFAP in addition to either fibronectin, reticulin or collagen type IV is not a known constituent of glioblastoma tissue. This provides evidence of a second mechanism of conversion of gene expression in gliomas.

Products of cells cultured from gliomas. IV. Extracellular matrix proteins of gliomas

Five primary and 3 established human glioma cell lines were cultured with ascorbate and examined for expression of extracellular matrix components. All lines except C6 expressed collagen as assessed by silver impregnation, immunofluorescence and lectin staining and expressed laminin and fibronectin. None expressed a lectin marker for endothelial cells. Both epithelial and mesenchymal collagens were expressed. While extracellular components of glioma lines resembled those of fibroblasts more closely than other cell types, subtle differences between gliomas and fibroblasts were present. These included more laminin and collagen type-IV antigenic reactivity and more 11-12 nm diameter extracellular fibrils from individual gliomas, and slight differences in spectra of low-molecular-weight extracellular proteins assessed by gel electrophoresis. One primary and two established glioma lines analysed for DNA content were aneuploid in contrast to diploid fibroblasts. Simultaneous expression of mesenchymal and epithelial markers suggests a dual differentiation potential of glioma cells. Results do not support an endothelial origin for cells cultured from gliomas.

The role of ascorbic acid in carcinogenesis

Vitamin C is an essential nutrient whose protective role in carcinogenesis has been discussed for more than 50 years. Epidemiologic studies suggest that the consumption of vitamin C-rich foods is associated with a lower risk of cancers of the esophagus and stomach. The observation that cancer patients have low leukocyte vitamin C levels led to therapeutic trials the results of which are controversial; the hypothesis that vitamin C acts like a drug must be questioned. On the other hand, ascorbic acid interacts with various tumor-inducing compounds, such as the precursors of N-nitroso compounds, to prevent the formation of tumors. Experiments with animals and cell cultures indicate that ascorbic acid can interfere with the metabolism of tumor promoters. It has also been postulated that ascorbic acid helps to prevent cancer by enhancing cellular immunity. In general, evidence suggests that vitamin C can inhibit the formation of some carcinogens.

Repeated establishment of diploid epithelial cell cultures from normal and partially hepatectomized rats

A number of liver epithelial cell cultures were established from 10 to 12-d-old sucklings, 6 to 8-wk-old young adults, or from 2 to 18-month-old partially hepatectomized rats. Improvements in the methods for cell isolation and culture yielded replicating cells from every experiment and they were maintained for different periods with regular passages. The proliferative potential in vitro of adult rat liver cells could be increased if the rats were subjected to partial hepatectomy before cell isolation. In the early passages, the majority of the cells were found to have a true diploid karyotype as studied by the Giemsa-banding technique. Under the culture conditions described, a very high percentage of cells remained in the diploid range for, in most cases, at least 4 months and in some cases for up to 6 months. Afterward, the karyotype was unstable, but no "crisis" period was seen before the cells became aneuploid. Until this time, the growth characteristics of the cells also followed a normal pattern showing density dependent inhibition of division and a lack of markers associated with malignancy. The cultured liver cells exhibited a number of liver specific properties when they were maintained as a confluent monolayer. The early passages of diploid epithelial cell cultures derived from normal and regenerating rat liver are good models for studies of the regulation of cell division and the changes that are related to carcinogenesis.

Primary epithelial cell cultures derived from canine prostate: isolation, culture, and characterization

Epithelial-cell-enriched primary cultures were established from canine prostate. Minced tissue was dissociated with 750 units/ml of collagenase in F12K tissue culture medium containing 1% fetal bovine serum. This treatment resulted in the gradual removal of stromal elements from the base of the epithelial cells. After 30 minutes of digestion, aggregates of epithelial cells free of stroma were dislodged from the minced pieces of prostate. These aggregates were washed and plated at high density in F12K plus 10% fetal bovine serum. After 12-16 hours in vitro the unattached cellular aggregates were removed from the culture dishes, washed, and reinoculated into new culture vessels containing fresh medium. After 48 hours in vitro, the aggregates had attached to the culture vessels and spread out to yield discrete patches of epithelial cells. By 120 hours in vitro the patches of cells had grown and coalesced to form a confluent monolayer of epithelial cells. Ultrastructural examination of these cultures indicated that adjacent cells were joined by desmosomes and tight junctions and had tonofilaments and microvilli, giving the cells an epithelial appearance. The cells contained rough endoplasmic reticulum, Golgi apparatus, and secretory granules similar to those of the epithelial cells in the intact organ. In addition, intracellular "blebs" containing acid phosphatase were observed in the monolayers and were found to increase in size and number with time in vitro. Differentiated function of the cultures was demonstrated by the presence of ornithine decarboxylase and acid phosphatase and the ability of the cultures to metabolize testosterone to primarily 5 alpha-reduced metabolites.

A fetal respiratory epithelial cell line for studying some problems of transplacental carcinogenesis in Syrian golden hamsters

Using repeated cloning and treatment with cis-HPL (200 micrograms/ml), an analogue of a procollagen precursor inhibitory to the growth of collagen-synthesizing cells of mesenchymal origin, clonally premature epithelial cell lines were isolated from fetal SGH lungs cultured on the 15th day of gestation. One of the cell lines, M3E3/C3, which has been extensively studied for biological characterization, developed poorly differentiated carcinomas in injected hamsters after transformation by MNNG. Moreover, when grown on collagen gel, this cell line indicated an obvious potency for in vitro differentiation in response to vitamin A by developing activated Golgi regions, well developed rER and a number of mucus-like granules. Since such a differentiative responses is expected to be definable in the light of respiratory epithelium developing in utero, this cell line may be useful for studying mechanisms of differentiation-dependent sensitivity of fetal organs to transplacental carcinogen exposure.

Collagen types in neuromuscular diseases

The striking proliferation of connective tissue characteristic of the muscular dystrophies can be attributed predominantly to an increase in endomysial and perimysial type III collagen. Carriers of muscular dystrophy occasionally revealed a slight increase in anti-type III collagen fluorescence, but no abnormalities in collagen disposition were observed in foetuses "at risk" for DMD. In contrast, the proportion of collagen types in neurogenic atrophies appeared normal although anti-type IV and V staining, which delineated the basement membrane, was very intense around atrophied fibres, as was also the case in small fibres in myopathic diseases. The detection of staining with anti-type III, IV and V collagens in splits which are sometimes observed in hypertrophied fibres in the muscular dystrophies supports the suggestion that abnormalities in collagen production, perhaps involving a defective modulation of myoblast-fibroblast expression, may be involved in the pathogenesis of these diseases.

Collagen synthesis in human fibroblasts: effects of ascorbic acid and regulation by hydrocortisone

The effects of hydrocortisone and ascorbic acid on collagen and noncollagen protein synthesis, and on growth were examined in fibroblasts derived from normal human dermis. When the medium was supplemented with 0.28 mM ascorbic acid, the apparent rate of collagen production increased 2-3 fold over the culture cycle. Ascorbic acid also caused a small increase in the apparent rate of synthesis of noncollagen protein and an elevation in growth rate and maximum cell density. Growth was not required for the increase in collagen production since addition of ascorbate to confluent cultures induced a similar increase. Hydrocortisone (1.5 microM) blocked the ascorbate-related increase in collagen production during growth and in confluent cultures. The hormone simultaneously increased the apparent rate of noncollagen protein production and maximum cell density, suggesting that the effect on collagen synthesis was specific. Inhibition of collagen production by hydrocortisone was observed only in the presence of ascorbate, while the increase in growth and noncollagen protein production occurred in the presence and absence of the vitamin.

Cultured human bronchial epithelial cells: blood group antigens, keratin, collagens, and fibronectin

Immunofluorescence and immunoperoxidase methods were used to identify constituents and products of cultured human bronchial epithelial cells and fibroblasts. Epithelial cells, but not fibroblasts, from patients with blood Types A or B reacted to the respective antisera to either the A or B blood group antigens. However, neither the epithelial cells nor the fibroblasts from patients with blood type O[H] reacted with the anti-H antisera. Epithelial cells in primary culture reacted with antibody to prekeratin proteins from human stratum corneum and fibroblasts did not react. Moreover, keratin filaments were assembled in vitro from proteins isolated from the epithelial cells. These immunological and biochemical data support previous morphological observations that human bronchial epithelial cells in primary culture shift progressively from a mucociliary epithelium to a keratinizing epithelium. Epithelial cells and fibroblasts could also be identified by their reactivity to anti-collagen antibodies. Fibroblasts reacted strongly with antibodies to Types I and III collagens and epithelial cells did not. On the other hand, epithelial cells reacted weakly with antibodies to Type IV collagen and fibroblasts were completely negative. Both epithelial cells and fibroblasts reacted with antibody to fibronectin; however, the distribution of fibronectin differed in the two cell types. In epithelial cells, fibronectin was restricted to the cell surface, whereas in fibroblasts it was found on the cell surface and in the extracellular matrix where fibrils of fibronectin were both cell associated and deposited on the surface of the dish where the fibroblasts had migrated.

Isolation, culture and characterization of epithelial cells derived from rat ventral prostate

Epithelial-cell enriched primary cultures have been established from rat ventral prostate (RVP). Minced ventral prostates were dissociated with 0.5% collagenase in F12K tissue culture medium containing 1% fetal bovine serum. This treatment resulted in the gradual removal of stromal elements from the base of the epithelial cells. After 60 minutes of digestion the aggregates of epithelial cells were washed and plated at high density in F12K plus 10% horse serum. After 48 hours in vitro the unattached cells were removed from the culture dishes, washed, and reinoculated into new culture vessels containing fresh medium. After 96 hours in vitro, the aggregates had attached to the culture vessels and spread out to yield discrete patches of epithelial cells. By 144 hours in vitro the patches of cells had grown and coalesced to form a semi-confluent monolayer of epithelial cells. Ultrastructrual examination of these cultures indicated that adjacent cells were joined by desmosomes and tight junctions and had formed "lumen-like structures" into which projected microvilli. In addition, the cells contained secretory granules and tonofilaments, giving them a morphological appearance similar to prostate epithelial cells in the intact organ. The primary cultures also retained histochemical activities for acid phosphatase, beta-glucuronidase, and succinic dehydrogenase that were similar to the intact organ.

Characterization of collagen synthesized by normal and chemically transformed rat liver epithelial cell lines

A rat liver epithelial cell line (K16) and a 2-[N-(acetoxyacetyl)amino]fluorine-transformed K16 cell line (W8) [Weinstein, I.B., Yamaguchi, R., Gerbert, R., & Kaighn, M.E. (1975) In Vitro 11, 130-141] synthesize and secrete similar quantities of collagenous proteins. The transformed cells produce more total protein so that the percent collagen produced is decreased compared to that of the parent cell line. The type of collagen produced by the transformants differed from that of the parent cell line. After limited pepsin digestion, the pepsin-resistant collagen molecules synthesized by K16 cells precipitated at 2.6 M NaCl and contained both alpha 1 (I) and alpha 2 chains in a 2.5:1 ratio. The collagen synthesized by the W8 cells precipitated at higher salt concentrations, and no pepsin-resistant alpha 2 chains could be demonstrated by CM-cellulose chromatography or gel electrophoresis. The cyanogen bromide peptides of the W8 alpha 1 chains did not cochromatograph with type I rat skin collagen cyanogen bromide peptides on CM-cellulose chromatography, whereas the alpha 1 chains of the K16 cells did cochromatograph. The conversion of procollagen to collagen was also decreased in the transformant cells. Therefore, the chemical transformation of K16 produced transformants with increased protein synthesis and altered collagen metabolism.

The effect of ascorbic acid on the nature and production of collagen and elastin by rat smooth-muscle cells

1. The effects of various concentrations of ascorbic acid on the quality and quantity of the insoluble extracellular matrices produced by two strains of cultured rat smooth-muscle cells were studied. 2. Ascorbic acid was necessary for the appearance of insoluble collagen in the extracellular matrix. 3. Secretion of soluble collagen continued in the absence of ascorbic acid, but this soluble collagen was markedly underhydroxylated. 4. The amount of insoluble collagen present in the matrix was directly related to the ascorbic acid concentration. 5. The insoluble collagen that appeared in the matrix under conditions where ascorbic acid was limiting was no more than 7% underhydroxylated. 6. In contrast, the amount of insoluble elastin produced was inversely proportional to the ascorbic acid concentration. 7. The elastin produced in the absence of ascorbic acid had the expected amino acid composition, but hydroxyproline was absent. 8. The hydroxyproline content of elastin was also directly dependent on the ascorbic acid concentration. 9. Ascorbic acid had variable effects on the quantity of glycoprotein(s) present in the matrix. 10. The appearance of insoluble collagen in the extracellular matrices produced by cultured human fibroblasts and calf endothelial cells was also completely dependent on the presence of ascorbic acid.