Localization of the human fibronectin (FN) gene on chromosome 8 by a specific enzyme immunoassay

IL-4 induces differentiation of human embryonic stem cells into fibrogenic fibroblast-like cells

BACKGROUND

Fibroblast heterogeneity is recognized, and fibroblasts from diseased tissues, including those of asthmatic subjects, have functional phenotypes that differ from normal tissue. However, progenitor-progeny relationships and the factors that control fibroblast differentiation are poorly defined.

OBJECTIVE

We sought to determine whether IL-4 could alter the functional phenotype of fibroblasts during their differentiation from stem/progenitor cells.

METHODS

Using a 3-dimensional collagen gel system, we obtained embryoid bodies derived from human embryonic stem cells and recovered spindle-shaped cells consistent with fibroblasts that had differentiated in the presence or absence of IL-4.

RESULTS

IL-4-induced fibroblast-like cells were more active in contraction of collagen gels, migration, and production of fibronectin than control (without IL-4) cells. IL-4-induced cells demonstrated less expression of miR-155, which modulated contraction, migration, and fibronectin production. These differences persisted in culture without further addition of IL-4, suggesting the differentiated phenotype might be a permanent alteration.

CONCLUSION

The current study demonstrates that IL-4 induces differentiation of stem/precursor cells into fibroblast-like cells that demonstrate a more fibrogenic phenotype, which is due to reduced expression of miR-155. These findings provide a novel mechanism for the persistent abnormalities in IL-4-related diseases and a novel target to regulate tissue remodeling by fibroblasts.

Reactive Nitrogen Species Augment Fibroblast-Mediated Collagen Gel Contraction, Mediator Production, and Chemotaxis

Reactive nitrogen species (RNS) such as peroxynitrite cause cellular injury and tissue inflammation. Excessive production of nitrotyrosine, which is a footprint of RNS, has been observed in the airways of patients with asthma and chronic obstructive pulmonary disease, disorders characterized by tissue remodeling. The aim of this study was to evaluate whether RNS can affect tissue remodeling through direct effects on fibroblasts, and to determine if these effects depend on production of transforming growth factor-beta (TGF-beta). To accomplish this, human fetal lung fibroblasts (HFL-1) were used to assess fibroblast-mediated contraction of floating gels and chemotaxis toward fibronectin. In addition, the ability of fibroblasts to release TGF-beta1, fibronectin, and vascular endothelial growth factor (VEGF) was assessed by enzyme-linked immunosorbent assay. Authentic peroxynitrite significantly augmented gel contraction (P < 0.01) and chemotaxis (P < 0.01) compared with control in a concentration-dependent manner. Similarly, the peroxynitrite donor 3-morpholynosidenonimine hydrochloride (SIN-1) also augmented gel contraction (P < 0.01). RNS also significantly increased TGF-beta1 (P < 0.01), fibronectin (P < 0.01), and VEGF (P < 0.01) release into the media in both 3D gel and monolayer culture. Anti-TGF-beta antibody reversed RNS-augmented gel contraction (P < 0.01) and mediator production (P < 0.01). Anti-TGF-beta antibody also partially, but significantly, reversed RNS-augmented chemotaxis toward fibronectin (P < 0.01). Finally, peroxynitrite enhanced expression of alpha5beta1 integrin, which is a receptor for fibronectin (P < 0.01), and neutralizing anti-TGF-beta antibody suppressed peroxynitrite-augmented alpha5beta1 expression (P < 0.01). These results suggest that RNS can affect the tissue repair process by modulating TGF-beta1.

Effect of cigarette smoke on fibroblast-mediated gel contraction is dependent on cell density

Cigarette smoke exposure has been associated with a variety of diseases, including emphysema. The current study evaluated the interaction of cell density and cigarette smoke extract (CSE) on fibroblast contraction of collagen gels. Protein levels of transforming growth factor (TGF)-beta1, fibronectin, PGE(2), and TGF-beta1 mRNA were quantified. Although both 5 and 10% CSE inhibited contraction by low-density fibroblasts (1 x 10(5) cell/ml), only 5% CSE augmented contraction in higher-density cultures (3-5 x 10(5) cells/ml). CSE also inhibited fibronectin and TGF-beta1 production in low-density cultures but stimulated fibronectin production in high-density cultures. Active TGF-beta1 was readily detectable only in higher-density cultures and was markedly augmented by 5% CSE. In contrast, although TGF-beta1 mRNA expression was inhibited in high-density cultures by 10% CSE, expression was increased in the presence of 5% CSE. These results suggest that CSE-induced inhibition of low-density fibroblast contraction is due to inhibition of fibronectin production, whereas CSE's stimulatory effect on high-density cells is the result of increased release of TGF-beta1. These effects may help explain the varied pathologies associated with exposure to cigarette smoke.

Ultrafine carbon black particles inhibit human lung fibroblast-mediated collagen gel contraction

Both acute and chronic exposure to particulates have been associated with increased mortality and morbidity from a number of causes, including chronic obstructive pulmonary disease and other chronic lung diseases. The current study evaluated the hypothesis that ultrafine carbon particles, a component of ambient particulates, could affect tissue repair. To assess this, the three-dimensional collagen gel contraction model was used. Ultrafine carbon black particles, but not fine carbon black, inhibited fibroblast-mediated collagen gel contraction. Although previous research has indicated that inflammatory effects of ultrafine carbon black particles are mediated by oxidant mechanisms, the current study suggests that ultrafine carbon black's inhibition of fibroblast gel contraction is mediated by the binding of both fibronectin and transforming growth factor (TGF)-beta to the ultrafine particles. Binding of TGF-beta was associated with a reduction in nuclear localization of Smads, indicative of inhibition of TGF-beta signal transduction. There was also a decrease in fibronectin mRNA, consistent with a decrease in TGF-beta-mediated response. Taken together, these results demonstrate the ability of ultrafine particles to contribute to altered tissue repair and extend the known mechanisms by which these biologically active particles exert their effects.

Fibronectin production by cultured human lung fibroblasts in three-dimensional collagen gel culture

In vivo, fibroblasts are distributed in a three-dimensional (3-D) connective tissue matrix. Fibronectin is a major product of fibroblasts in routine cell culture and is thought to regulate many aspects of fibroblast biology. In this context, we sought to determine if the interaction of fibroblasts with a 3-D matrix might affect fibronectin production. To examine this hypothesis, fibronectin production by fibroblasts cultured in a 3-D collagen gel or on plastic dishes was measured by ELISA. Fibroblasts in 3-D gel culture produced more fibronectin than those in monolayer culture. Fibroblasts in 3-D culture produced increasing amounts of fibronectin when the collagen concentration of the gel was increased. The 3-D nature of the matrix appeared to be crucial because plating the fibroblasts on the surface of a plastic dish underneath a collagen gel was not different from plating them on a plastic dish in the absence of collagen. In addition to increased fibronectin production, the distribution of the fibronectin produced in 3-D culture was different from that of monolayer culture. In monolayer culture, more than half of the fibronectin was released into the culture medium. In 3-D culture, however, approximately two-thirds remained in the collagen gel. In summary, the presence of a 3-D collagen matrix increases fibroblast fibronectin production and results in greater retention of fibronectin in the vicinity of the producing cells.

Lipopolysaccharide increases fibronectin production and release from cultured lung fibroblasts partially through proteolytic activity

Fibronectin is a major product of fibroblasts and can mediate diverse functions including wound healing. Chronic bacterial infections are generally associated with a marked decreased in the ability to repair. We therefore hypothesized that bacterial endotoxin, lipopolysaccharide (LPS), might alter fibroblast fibronectin production. LPS augmented fibronectin production by fibroblasts and also stimulated the release of fibronectin from cell layers. An increase in new protein synthesis appeared to account for part of the increased fibronectin, because the inhibitor of protein synthesis, cycloheximide, inhibited the increase in total production of fibronectin. Cycloheximide did not attenuate the increased release of fibronectin into the culture medium. This increased release appeared to be caused, at least in part, by fragmentation of fibronectin by proteases contained in LPS preparations. In this regard all preparations of LPS tested were found to cleave fibronectin. Finally, zymograms indicated that LPS could also cleave gelatin with at least two bands of proteolytic activity but that it did not cleave bovine serum albumin or ovalbumin. These results indicate that the ability of bacterial products to alter fibronectin production and to degrade this macromolecule may account for altered wound repair that occurs with chronic bacterial infection.

Pentosome--a new connective tissue component--is a subunit of amyloid P

A new minute connective tissue structure, referred to as "pentosome", has been investigated by electron microscopy and its nature has been examined by immunoperoxidase tests. Pentosomes are 3.5-nm wide, particulate structures that have been observed in the posterior chamber of the eye, the connective tissue spaces of the mouse foot-pad and the matrix of the mouse EHS tumor. They are usually found in the vicinity of microfibrils whether they are free or associated with elastic fibers. They tend to be organized into groups forming a three-dimensional semi-crystalline lattice at 10-nm intervals, but are connected by fine filaments. At high magnification, pentosomes appear as hollow structures composed of two parallel pentagons, which respectively measure 2.7 and 3.5 nm, and are held together by a cross-bar. A series of immunoperoxidase tests has only shown antigenicity against a serum protein, the amyloid P component. However, pentosomes are only about one-third the size of the 8.5-nm wide, disk-like segments of the amyloid P molecule. Since they could be subunits of these molecules, such subunits were prepared and compared with pentosomes; they appeared to be identical. It is concluded that the pentosomes found in connective tissue are AP subunits.

Lack of heparan sulfate proteoglycan in a discontinuous and irregular placental basement membrane

A discontinuous basement membrane of variable width that surrounds spongiotrophoblast cells of rat placenta was examined for the presence of type IV collagen, laminin, a heparan sulfate proteoglycan, entactin, and fibronectin using monospecific antibodies or antisera and the indirect peroxidase technique. At the level of the light microscope, the basement membrane was immunostained for type IV collagen, laminin, entactin, and fibronectin. Heparan sulfate proteoglycan immunostaining, however, was virtually absent even after pretreatment of sections with 0.1 N acetic acid, pepsin (0.1 microgram/ml) or 0.13 M sodium borohydride. Examination in the electron microscope confirmed the lack of immunostaining for heparan sulfate proteoglycan, whereas the other substances were mainly localized to the lamina densa part of the basement membrane. The absence of heparan sulfate proteoglycan in this discontinuous and irregular basement membrane even though type IV collagen, laminin, entactin, and fibronectin are present, suggests that heparan sulfate proteoglycan may have a structural role in the formation of basement membrane.

Fine structure of the glomerular basement membrane and immunolocalization of five basement membrane components to the lamina densa (basal lamina) and its extensions in both glomeruli and tubules of the rat kidney

Electron microscopic immunostaining was used to examine the localization of type IV collagen, laminin, entactin , heparan sulfate proteoglycan, and fibronectin within the basement membranes of the rat kidney. In preliminary experiments, various methods of processing formaldehyde-fixed kidney were compared using antilaminin antiserum and the indirect immunoperoxidase method. Little or no laminin immunostaining of the glomerular basement membrane was present in sections unless they had been frozen-thawed; and even in this case, the immunostaining was light in comparison to that of basement membranes in adjacent tubules. However, when frozen-thawed sections were treated with 0.5% sodium borohydride, immunostaining was then as strong in glomerular as in tubular basement membranes. Accordingly, this treatment was applied to frozen-thawed sections before immunostaining for any of the substances under study. Immunostaining of the glomerular basement membrane for each of the five substances was fairly uniform throughout the lamina densa (also called basal lamina), but uneven in the lamina lucida interna and externa (also called lamina rara interna and externa) in which stained bands extended from the lamina densa. Similarly in the basement membranes of tubules, immunostaining for the five substances was localized to the lamina densa and bands extending into the lamina lucida. When the ultrastructure of the glomerular basement membrane was examined, three structures were found: (1) a network of 4-nm-thick "cords," which seems to be the main component; the cords are closely packed in the lamina densa and more loosely arranged in the lamina lucida interna and externa; (2) straight, hollow 7-10-nm-thick structures referred to as " basotubules "; and (3) 3.5-nm elements composed of minute paired rods, referred to as "double pegs." The distribution of the cords, but not that of the other two structures, was related to the immunostaining pattern. It is concluded that (1) to fully reveal the antigenicity of the glomerular basement membrane, frozen-thawed sections must be treated with sodium borohydride prior to immunostaining, possibly because this basement membrane is more compact than the others; and (2) in both glomerular and tubular basement membranes, type IV collagen, laminin, entactin , heparan sulfate proteoglycan and fibronectin are colocalized in the lamina densa and its extensions to the laminae lucidae . Since the distribution of the cords corresponds to that of immunostaining, it is likely that the five substances are present within the cords.

Regulation of fibronectin biosynthesis by glucocorticoids in human fibrosarcoma cells and normal fibroblasts

When treated with the synthetic glucocorticoid dexamethasone, HT1080 human fibrosarcoma cells show changes in morphology, adhesion, and the extracellular matrix. Dexamethasone treatment results in a tenfold increase in the rate of fibronectin biosynthesis in HT1080 cells and a twofold increase in untransformed, normal human fibroblasts. Maximal induction levels are attained within one cell generation, while decay of the response requires several cell cycles. Pulse-chase studies showed that most of the newly synthesized fibronectin is secreted into the medium. The glucocorticoid antagonist, RU-486, blocks the dexamethasone-induced changes but does not alter the basal rate of fibronectin production. Therefore, fibronectin biosynthesis appears to be controlled by two distinct mechanisms--one, regulating basal rates of fibronectin production, which is transformation-sensitive and glucocorticoid-independent; and another, which is mediated by the glucocorticoid receptor, resulting in elevated rates of fibronectin biosynthesis upon dexamethasone treatment both in normal fibroblasts and in HT1080 cells.

Assignment of the genes for mouse type I procollagen to chromosome 16 using mouse fibroblast-Chinese hamster somatic cell hybrids

Somatic cell hybrids between mouse and Chinese hamster fibroblasts have been used to identify the chromosome responsible for the synthesis of both mouse type I procollagen subunit chains (MCOLA1 and MCOLA2). Thirty-one separate hybrid clones and subclones from ten separate hybridization events were isolated in hypoxanthine-aminopterin-thymidine (HAT) selection medium and were used for detailed gene-mapping studies. ELISA and "Western blotting" immunochemical analysis were used to detect the production of mouse type I procollagen in each hybrid clone. Mouse and Chinese hamster chromosomes were identified in each hybrid clone by trypsin-Giemsa banding of metaphase chromosome spreads and by isozyme analysis. We have found that mouse type I procollagen production segregates concordantly with mouse superoxide dismutase-1, previously mapped to mouse chromosome 16, and with the presence of mouse chromosome 16 karyotypically. Western blotting immunochemical analysis of the separated mouse procollagen chains produced by each hybrid line demonstrated that apparently the genes for both subunit chains are located on the same chromosome. These studies, therefore, assign the structural genes for mouse type I procollagen pro alpha 1 (MCOLA1) and pro alpha 2 (MCOLA2) chains to mouse chromosome 16.

Human skin collagenase: assignment of the structural gene to chromosome 11 in both normal and recessive dystrophic epidermolysis bullosa cells using human-mouse somatic cell hybrids

Somatic cell hybrids between mouse cells and human normal skin and corneal fibroblasts and recessive dystrophic epidermolysis bullosa (RDEB) skin fibroblasts have been used to assign the structural gene for collagenase to its human chromosome. A total of 46 hybrid subclones from several hybridization events were isolated in hypoxanthine-aminopterin thymidine (HAT) selection medium and used to measure the production of human collagenase by a specific radioimmunoassay. We have found that both the normal and RDEB human collagenase gene maps to human chromosome 11. This indicates that the abnormal collagenase produced by RDEB cells is probably not a totally distinct form of the enzyme, but is a structural mutation of the normal collagenase enzyme.

Localization of type IV collagen, laminin, heparan sulfate proteoglycan, and fibronectin to the basal lamina of basement membranes

Electron microscopic immunostaining of rat duodenum and incisor tooth was used to examine the location of four known components of the basement-membrane region: type IV collagen, laminin, heparan sulfate proteoglycan, and fibronectin. Antibodies or antisera against these substances were localized by direct or indirect peroxidase methods on 60-microns thick slices of formaldehyde-fixed tissues. In the basement-membrane region of the duodenal epithelium, enamel-organ epithelium, and blood-vessel endothelium, immunostaining for all four components was observed in the basal lamina (also called lamina densa). The bulk of the lamina lucida (rara) was unstained, but it was traversed by narrow projections of the basal lamina that were immunostained for all four components. In the subbasement-membrane fibrous elements or reticular lamina, immunostaining was confined to occasional "bridges" extending from the epithelial basal-lamina to that of adjacent capillaries. The joint presence of type IV collagen, laminin, heparan sulfate proteoglycan, and fibronectin in the basal lamina indicates that these substances do not occur in separate layers but are integrated into a common structure.

Fibronectin in human bronchopulmonary lavage fluid. Elevation in patients with interstitial lung disease

Fibronectin is a major adhesive and opsonic glycoprotein found in plasma and tissues. Because this molecule appears to mediate a number of interactions between cells and extracellular matrix, and because the interstitial lung disease are characterized by marked derangements of the pulmonary extracellular matrix, we evaluated fibronectin in the lower respiratory tract in patients with these disorders. Fibronectin could be detected in the bronchoalveolar lavage fluid of normals (11/11), as well as those with noninterstitial lung diseases (18/18), idiopathic pulmonary fibrosis (21/21), sarcoidosis (20/20), and other interstitial lung diseases (22/22). Compared with normal and those with noninterstitial lung disease, the levels in bronchoalveolar lavage of patients with interstitial disease were significantly higher (P less than 0.01), all comparisons). This was true only for bronchoalveolar lavage fibronectin; plasma levels were similar in all study groups (P greater than 0.2, all comparisons). The lavage fluid fibronectin was intact antigenically and retained collagen binding capability, although in some cases of interstitial disease, the presence of lower molecular weight fragments suggested some degradation. Thus, fibronectin is a normal constituent of the epithelial fluid of the lower respiratory tract and is present in increased amounts in a significant number of individuals with interstitial lung disease.

Species-specific monoclonal antibodies in the assignment of the gene for human fibronectin to chromosome 2

Using three different species-specific monoclonal antibodies we have studied, in human-mouse and human-hamster somatic cell hybrids, the correlation between the presence of different human chromosomes and the ability to release human fibronectin into the tissue culture medium. Presence of human fibronectin was determined by an affinity-radioimmunoassay. In addition, tissue culture media of the different hybrids were separated on SDS-polyacrylamide gels, the proteins were blotted onto a nitrocellulose sheet and human fibronectin visualized by an immunoenzymatic technique. Karyology and determination of isoenzyme markers of specific human chromosomes show that the ability to produce human fibronectin segregated with the presence of human chromosome 2.