Studies of fibronectin synthesized by cultured chick hepatocytes

Circulating Exosomal miR-144-3p from Crohn’s Disease Patients Inhibits Human Umbilical Vein Endothelial Cell Function by Targeting FN1

Background

Crohn's disease (CD) is a chronic nonspecific inflammatory disease with unknown pathogenesis and vascular changes associated with the progression of CD. Many studies have shown that miRNAs participate in the development of CD. However, the effect of miRNAs in circulating exosomes on vascular endothelial cells in CD has not been investigated. Our study is aimed at identifying the differential miRNAs in circulating exosomes in CD and exploring their potential roles in human umbilical vein endothelial cells (HUVECs).

Methods

In our study, exosomes were extracted from circulating blood to identify differential miRNAs. After in vitro transfection of HUVECs with miR-144-3p mimics and inhibitors and the corresponding controls, cell counting kit-8, wound healing, Transwell migration, and tube formation assays were performed to study the viability, migration, and angiogenesis of HUVECs. Furthermore, bioinformatics analysis was used to predict miRNA targets. Western blotting was used to determine protein expression. In addition, exogenous supplementation with the fibronectin 1 (FN1) protein rescued the effects of miR-144-3p on changes in cell function in vitro.

Results

miR-144-3p was significantly increased in circulating exosomes of patients with CD compared with those in the control group. The promotion or inhibition of miR-144-3p correspondingly abolished or accelerated cell viability, migration, and angiogenesis. FN1 is a significant target of miR-144-3p, and exogenous FN1 administration improved the function of HUVECs in vitro.

Conclusions

Circulating exosomal miR-144-3p from patients with active CD contributes to vascular endothelial dysfunction by affecting the gene expression of FN1. These findings suggested that circulating exosomal miR-144-3p could be a potential biological marker for CD.

Using proteomics to uncover extracellular matrix interactions during cardiac remodeling

The left ventricle (LV) responds to a myocardial infarction with an orchestrated sequence of events that result in fundamental changes to both the structure and function of the myocardium. This collection of responses is termed as LV remodeling. Myocardial ischemia resulting in necrosis is the initiating event that culminates in the formation of an extracellular matrix (ECM) rich infarct scar that replaces necrotic myocytes. While the cardiomyocyte is the major cell type that responds to ischemia, infiltrating leukocytes and cardiac fibroblasts coordinate the subsequent wound healing response. The matrix metalloproteinase family of enzymes regulates the inflammatory and ECM responses that modulate scar formation. Matridomics is the proteomic evaluation focused on ECM, while degradomics is the proteomic evaluation of proteases as well as their inhibitors and substrates. This review will summarize the use of proteomics to better understand matrix metalloproteinase roles in post myocardial infarction LV remodeling.

Stimulation of chick hepatocyte fibronectin production by fibroblast-conditioned medium is due to interleukin 6

Interleukin-6 (IL6) is produced by different cell types, including monocytes and fibroblasts. We show that recombinant human IL6 (rhIL6) and chick fibroblast conditioned medium stimulate plasma fibronectin (PFn) and PFn mRNA production by cultured chick hepatocytes in a dose-dependent manner. Lipopolysaccharide (LPS) treatment of fibroblast cultures induces higher levels of the PFn stimulating activity. These effects are blocked by preincubation of either rhIL6 or LPS-stimulated chick fibroblast conditioned medium with anti-rhIL6 antibody before treatment of hepatocytes, indicating that the conditioned medium contains chick fibroblast-derived IL-6 (cfIL6). Further, LPS induces fibroblast production of a proportional increase in cfIL6 detectable by a human IL6 ELISA. cfIL6 maximally stimulates chick hepatocyte PFn production by 24 h (4.5-fold). Dexamethasone acts more rapidly, but maximal stimulation is only 2.3-fold. Hepatocyte Fn mRNA levels are even more substantially stimulated by dexamethasone and cfIL6 (up to 8.9- and 18.5-fold by 12 h, declining to 2.3 and 4.2-fold by 24 h, respectively). The effect cfIL6 with or without dexamethasone on hepatocyte PFn levels are comparable. These observations are consistent with the role of IL6 as a major mediator of acute phase protein production.

Biological markers as indicators of exposure and pneumoconiotic risk: prospective study

This research is designed to evaluate a number of biological markers to estimate harmful exposure on coal miners from different mining regions in France and to relate the outcome to differences in prevalence of coal worker pneumoconiosis (CWP) between these regions. Eight epidemiological groups of active and ex-miners (smokers and non-smokers) have been selected in the French collieries (North, Lorraine and Provence) according to their occupational and pneumoconiotic status. The following biomarkers have been evaluated: cellularity of sputum, elementary analysis of particles in TEM/EDAX, plasma neutral metalloendo-peptidase elastase type (NMEP), leucocyte elastase (HLE), fibronectin (FN) and elastin peptides. Pulmonary alveolitis, expressed by sputum cellularity, is different between active workers groups but not related to the general background of pneumoconiosis prevalence in the French collieries. In the plasma parameters, fibronectin, HLE and NMEP significantly increased in all groups of coal mine workers as compared to the control group, except for fibronectin parameter in Lorraine collierie. The degree of increase of these parameters allow us to discriminate the different groups and suggest that plasma FN, HLE and NMEP may be considered as biological markers of chronic inhalation of coal mine dust particles. The decrease of elastin peptides level in the Lorraine group alone suggests a specific alteration of elastin metabolism. These parameters were not related to the development of pneumoconiosis and its degree of severity.

Rat hepatocytes in primary culture synthesize and secrete cellular fibronectin

Fibronectins, involved in cell-matrix interactions and cell attachment, are glycoproteins which show a remarkable heterogeneity, due to alternative splicing. The type III-related domains, ED-A and ED-B, are present in cellular fibronectin in a variety of ratios whereas they are absent in circulating plasma fibronectin. Fibronectin synthesis by hepatocytes which are accepted as suppliers of plasma fibronectin was studied in primary cultures during a 6-day culture period. Using site-specific antibodies we demonstrate that rat hepatocytes are also able to synthesize and secrete fibronectin bearing the ED-A domain from Day 3 on after inoculation. By immunocytological characterization of the hepatocyte monolayer with antibodies directed against desmin, laminin, collagen IV, alpha-SM-actin, or ED-1 or factor VIII-related antigen, contaminating mesenchymal hepatic cell-types as a source for cellular fibronectin production could be ruled out. Dexamethasone treatment caused enhanced fibronectin synthesis and cellular fibronectin was already detectable at Day 1 after plating. Elevation of cellular fibronectin synthesis after prolonged culture-terms and by dexamethasone could also be demonstrated on mRNA steady-state level, using ED-A cDNA as a probe in hybridization analysis. Dot blot hybridisation proved a prominent response of cellular fibronectin mRNA level to dexamethasone at Day 1 when dexamethasone treatment resulted in an increased contribution of ED-A-positive fibronectin transcripts to total fibronectin mRNA level.

Adrenocorticotrophic hormone fails to alter plasma fibrinogen and fibronectin values in calves but does so in rabbits

The intramuscular administration of adrenocorticotrophic hormone (ACTH) to calves, in either a short-acting form (cosyntrophin) or a longer-acting form (ACTHAR Gel), failed to induce any alteration in circulating fibrinogen or fibronectin values, despite marked elevations in plasma cortisol concentrations. With the longer-acting ACTH, plasma cortisol was elevated for at least 12 h following treatment and induced the expected physiological response of an elevation in blood glucose. In contrast, both forms of ACTH induced marked increases (p < 0.01) in plasma fibrinogen and fibronectin when administered to rabbits. The elevation in the circulating levels of these proteins was first observed 24 h after ACTH administration, by which time plasma corticosteroid values had returned to pre-treatment values. With both ACTH preparations the increases in the circulating levels of these proteins were sustained for at least 96 h. The results suggest that, in cattle, the well-recognized increases in plasma fibrinogen values following stress are not associated with the concomitant increase in plasma cortisol. Further, the results clearly illustrate the marked species differences in the response of acute-phase reactant proteins to elevated glucocorticoids.

DNase I hypersensitive sites of the 5' region of the fibronectin gene of the liver of the rat

We have mapped the DNase I hypersensitive sites (DH-sites) of the 5' region of the fibronectin (FNT) gene of the liver of the rat. These sites are not detectable in the cerebral hemisphere of the rat. Northern blot hybridization of the gene shows the presence of a 8 kb transcript in the liver which is induced by dexamethasone. Nuclear run on transcription shows that transcription of the FNT gene is much lower than that of the albumin gene in the liver. Gel mobility shift assay using nuclear extract of the liver shows the presence of a trans-acting factor which binds to the cAMP responsive element which overlaps with a DH-site in the region. There is thus good correlation between DH-sites of the FNT gene and its transcription in the liver.

Dexamethasone modulates alpha 2-macroglobulin and apolipoprotein E gene expression in cultured rat liver fat-storing (Ito) cells

Fat-storing (Ito) cells are perisinusoidal liver cells thought to play a central role in vitamin A metabolism and fibrongenesis. Glucocorticoids have been shown to be beneficial in the treatment of certain types of liver diseases by delaying the development of cirrhosis. To study the regulatory effects of dexamethasone on Ito cell gene expression, Ito cells were isolated from normal rat liver and primary cultures were established. The effect of dexamethasone on the synthesis of alpha 2-macroglobulin, apolipoprotein E, fibronectin and actin was examined. Protein synthesis was studied both at the protein level and at the RNA level by means of biosynthetic labeling, immunoprecipitation followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by Northern blot analysis of total RNA. After exposure to dexamethasone for 20 hr, alpha 2-macroglobulin protein synthesis was increased threefold, whereas apolipoprotein E expression was decreased 80%. Biosynthesis of fibronectin remained unaffected by hormone treatment. The dexamethasone effect became detectable 5 hr after beginning the exposure. Deinduction kinetic experiments showed that the glucocorticoid effect was detectable more than 12 hr after the replacement of the dexamethasone-containing culture medium by medium without the hormone. Corresponding to the data obtained at the protein level, dexamethasone increased the steady-state levels of alpha 2-macroglobulin-specific messenger RNA and reduced apolipoprotein E-specific transcripts, whereas fibronectin and actin messenger mRNA remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of fibronectin and laminin by different types of mouse glial cells cultured in a serum-free medium

The expression of fibronectin and laminin by cultured glial cells was studied. The glial culture from neonatal mouse cerebra maintained in a chemically defined, serum-free medium consisted of type-1 astrocytes, oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells, oligodendrocytes and type-2 astrocytes. Double-labelling immunofluorescent experiments performed using the mixed glial culture indicated that fibronectin and laminin are expressed in different patterns among the glial subtypes. The staining intensities with anti-fibronectin or anti-laminin antibodies decreased in the order: type-1 astrocytes, O-2A progenitor cells and type-2 astrocytes. Both molecules were deposited in a fibrillar matrix underneath type-1 astrocytes, whereas only intracytoplasmic localization of these molecules was observed with O-2A progenitor cells and type-2 astrocytes. Western blot analysis showed that glial fibronectin has a slightly higher molecular weight than mouse plasma fibronectin (230 kDa) and that glial laminin is a variant with a 220 kDa B chain present and the 400 kDa A chain missing. Using enzyme-linked immunosorbent assays (ELISA), these molecules were detected in the glial extracellular matrix at the concentration of 4 ng/10(6) cells. A large amount of fibronectin (82 ng/10(6) cells) was secreted into the culture medium, while secretion of laminin was not detected.

Quantitative change in fibronectin in cultured müllerian mesenchymal cells in response to diethylstilbestrol and müllerian-inhibiting substance

I report on the synthesis of fibronectin in the developing chick Müllerian duct mesenchymal cells. Before the differentiation of female chick Müllerian duct, the amount of fibronectin in the cells of the right duct is 44% lower than in the left duct. While after differentiation, the amount of fibronectin in the right duct is 29% lower, as compared to the left duct. Estrogenic hormone diethylstilbestrol (DES) treatment was carried out at the 5th day of incubation when both female Müllerian ducts were undifferentiated. Three days after DES treatment, the regression of the right duct was prevented, and the amount of fibronectin was induced by 89%, while induction in the left duct was 11%. Eight days after DES administration, the amount of fibronectin in the right and left Müllerian duct was induced by 150 and 76%, respectively. After DES treatment in the male embryo, both Müllerian ducts were retained, and the capacity for fibronectin synthesis was preserved. Application of the indirect immunocytochemical labeling technique revealed Müllerian-inhibiting substance (MIS) binding sites on the membrane of the Müllerian mesenchymal cells. The addition of chick MIS in the culture medium reduced the amount of detectable fibronectin in the cultured mesenchymal cells. The synthesis of fibronectin in intestinal mesenchymal cells was not affected by DES or MIS.

Biosynthesis and secretion of fibronectin in the cultured mesenchymal cells of the developing chick müllerian duct

We have developed a method to separate and isolate the mesenchymal cells from the epithelial cells in the left Müllerian duct of the developing chick. We then cultured the mesenchymal cells in a serum-free medium. Through an enzyme-linked immunosorbent assay, we detected fibronectin synthesis and release into the medium at stages of Müllerian duct development. Our results demonstrate that the amount of fibronectin secreted by cultured cells gradually decreased in accordance with Müllerian duct differentiation. Similar observations found in the developing embryonic intestine indicate that the highest fibronectin synthesis occurs during early stages of development, when morphogenetic movement and mesenchymal-epithelial interaction are prominent features of embryonic organ differentiation and growth.

Stimulation of rat hepatocyte fibronectin production by monocyte-conditioned medium is due to interleukin 6

In this report, conditioned media from LPS-stimulated monocytes increased rat hepatocyte production of fibronectin (Fn) in a dose-dependent manner. Preincubation of the conditioned media with anti-IL-6, but not with anti-IL-1 alpha, anti-IL-1 beta, or anti-TNF, completely neutralized the Fn-stimulating activity. 10-100 pg/ml of rIL-6 was sufficient to increase Fn production. Neither IL-1 nor TNF had an effect on Fn production. The Fn-stimulating activity of IL-6 could be specifically neutralized only with anti-IL-6, but not with anti-IL-1 or anti-TNF. The increased Fn produced was shown to be of the plasma rather than the cellular form. These results demonstrate that IL-6 is the factor in monocyte-conditioned media that stimulates Fn production, and that IL-6 is the monokine tested with such activity.

Alternative splicing of chicken fibronectin in embryos and in normal and transformed cells

To study the alternative splicing of fibronectin during embryogenesis and oncogenic transformation, we isolated cDNA clones of chicken fibronectin. The partial amino acid sequence deduced from sequencing of these clones showed that, overall, chicken fibronectin is approximately 80% identical with mammalian fibronectins. However, two of the three known regions of alternative splicing differed from this average. The V region was significantly more divergent, and RNA from embryonic chicken liver showed a pattern of V exon splicing which was distinct from that seen in human or rat fibronectins. In contrast, the EIIIB segment was very highly conserved (96%). As in mammals, this segment and another (EIIIA) were alternatively spliced in a cell-type-specific fashion. EIIIA+ and EIIIB+ species were almost absent in liver but predominated in total embryo RNA at all times from 2.5 to 11 days postfertilization. We also examined the possible contributions of fibronectin splicing and integrin receptor expression to the loss of fibronectin on oncogenic transformation. We detected little change in fibronectin splicing, other than a slight increase in representation of EIIIB+ species in fibroblasts after transformation by Rous sarcoma virus. It was also established that the overall reduction in fibronectin mRNA level observed after transformation was not accompanied by a decrease in integrin mRNA levels, indicating that fibronectin and integrin receptors are not coordinately regulated at the transcriptional level.

Alternative splicing of chicken fibronectin in embryos and in normal and transformed cells

To study the alternative splicing of fibronectin during embryogenesis and oncogenic transformation, we isolated cDNA clones of chicken fibronectin. The partial amino acid sequence deduced from sequencing of these clones showed that, overall, chicken fibronectin is approximately 80% identical with mammalian fibronectins. However, two of the three known regions of alternative splicing differed from this average. The V region was significantly more divergent, and RNA from embryonic chicken liver showed a pattern of V exon splicing which was distinct from that seen in human or rat fibronectins. In contrast, the EIIIB segment was very highly conserved (96%). As in mammals, this segment and another (EIIIA) were alternatively spliced in a cell-type-specific fashion. EIIIA+ and EIIIB+ species were almost absent in liver but predominated in total embryo RNA at all times from 2.5 to 11 days postfertilization. We also examined the possible contributions of fibronectin splicing and integrin receptor expression to the loss of fibronectin on oncogenic transformation. We detected little change in fibronectin splicing, other than a slight increase in representation of EIIIB+ species in fibroblasts after transformation by Rous sarcoma virus. It was also established that the overall reduction in fibronectin mRNA level observed after transformation was not accompanied by a decrease in integrin mRNA levels, indicating that fibronectin and integrin receptors are not coordinately regulated at the transcriptional level.

Involvement of leukocyte and glucocorticoid in the acute-phase response of angiotensinogen

Plasma levels of angiotensinogen were significantly increased in rats following treatment with lipopolysaccharide (LPS). However, no such acute-phase response in the plasma angiotensinogen level was induced in hypophysectomized rats. Implantation of peritoneal exudate cells (PEC), which had been collected from rats treated with i.p. injection of LPS and glycogen, into the peritoneal cavities of normal rats also caused elevation of plasma angiotensinogen levels. No significant changes in plasma levels of corticosterone were observed in rats receiving either LPS or LPS-stimulated PEC. These results indicate that the acute-phase response of angiotensinogen is mediated by leukocytes-derived cytokine, and glucocorticoid is essential for its stimulatory effect on the hepatic production of angiotensinogen.

Measurement of connective tissue parameters in serum for diagnosis and follow-up of liver fibrosis

Hepatic fibrogenesis, i.e. activated synthesis and excessive intercellular deposition of connective tissue molecules (collagens, adhesive glycoproteins, proteoglycans) occurs in chronic alcoholic and viral liver injury and, less frequently, in some other conditions. The process may be monitored biochemically by the radioimmunoassay of some connective tissue molecules or their fragments and by the measurement of the activity of certain enzymes in serum. Currently, the radioimmunoassay of the aminoterminal propeptide of type III procollagen in serum reflects best the activity of liver fibrogenesis. The serum level of laminin, a high molecular weight basement membrane glycoprotein, was found to be correlated with an elevated portal venous pressure.

Fibronectin during thyroid hormone replacement therapy

Hemostasis may be affected by thyroid function in various ways. We studied plasma concentration of Fibronectin in 13 untreated patients after total thyroidectomy due to thyroid carcinoma. Fibronectin levels were significantly decreased compared to an equal numbered group of healthy volunteers (p 0.0005). The same patients were studied again after an oral thyroid replacement of 200 micrograms L-thyroxine/d over at least six weeks. Fibronectin had increased significantly, compared to untreated patients and controls resp. Furthermore, a significant positive correlation was found between plasma concentrations of Fibronectin and total T4 (r = 0.92; y = 6.617 + 0.52x). In contrast Factor V activity was low in untreated patients but normal during high dose replacement therapy. No correlation was found between Factor V and thyroid hormone concentrations. We discuss the relation between fibronectin plasma levels and thyroid hormones.

Effect of hepatocyte-stimulating factor and glucocorticoids on plasma fibronectin levels

We evaluated the effects of hepatocyte-stimulating factor (HSF) and a glucocorticoid (dexamethasone) on changes in the levels, in vivo and in vitro, of plasma fibronectin (Fn), a glycoprotein that is synthesized and secreted by hepatocytes. In turpentine-treated chickens, plasma levels of Fn, which peaked at 48 h (whereas fibrinogen levels were maximum at 72 h) rose 200-250% over basal levels, whereas albumin levels decreased by 20-40%. Corticosterone levels in serum samples taken between 5 and 48 h after injection revealed a 124% increase in hormone levels at 24 h in turpentine-treated chickens. We also showed that circulating HSF levels were maximal 8 to 12 h after injection and that HSF activity, as assessed by molecular-exclusion chromatography, was eluted in the 30-45 kDa range. Addition of either serum-derived HSF or dexamethasone (2 nM) to chick hepatocyte cultures resulted in a 130-150% increase in secreted Fn as well as in fibrinogen. When HSF and dexamethasone were added together, a 360-489% increase in the secreted levels of both proteins was found. Chicken mononuclear phagocytic cells treated with lipopolysaccharide secreted an HSF activity that was eluted in two peaks, a minor peak at approximately 70 kDa and a major peak in the 25-40 kDa range. Addition of mononuclear-cell-derived HSF resulted in a greater increase in Fn levels than did the addition of serum HSF. These findings indicate that Fn, like fibrinogen, is an acute-phase protein, the production of which, at least in chickens, is stimulated by HSF and glucocorticoids in an additive manner.

Fibronectin is synthesized as an acute phase reactant in rat hepatocytes

Elevated concentrations of fibronectin were found in plasma of rats under different acute phase conditions. Untreated animals showed a plasma fibronectin concentration of 150 +/- 50 mg/l, which increased to 412 +/- 59 mg/l 24 h after subcutaneous injection of turpentine. The time course of the changes in plasma fibronectin concentration showed a peak at 24 h and a decline to normal concentrations 72 h after turpentine treatment. Additional stimulation by dexamethasone resulted in plasma fibronectin concentrations of 661 +/- 49 mg/l. No or only slight elevations of fibronectin concentrations were observed after treatment with adrenaline, thyroxine and triiodothyronine as compared with saline-injected animals. The common identity of plasma fibronectin in controls, turpentine and turpentine-dexamethasone-treated animals was shown by slab gel electrophoresis under nonreducing conditions, followed by western blot and immunofluorescence staining. One dimensional immunoelectrophoresis performed with polyclonal antibodies to human fibronectin cross-reacting with rat fibronectin (shown by Ouchterlony gel diffusion) revealed identical precipitation lines for the plasma of control and acute phase animals. Hepatocytes of turpentine-pretreated rats show a threefold increase of [14C]valine incorporation into total protein and a fourfold increase of immunoreactive radioactively labeled fibronectin in the culture medium, compared with control hepatocyte cultures. These results point to the role of hepatocytes in the synthesis of plasma fibronectin, which behaves in rats as an acute phase reactant.

Evidence that chicken antithrombin III is a developmentally regulated glycoprotein synthesized by hepatocytes

Antithrombin III is the principal circulating active-site inhibitor of thrombin and other serine proteinases. We studied a protein synthesized and secreted by cultured chick embryo hepatocytes that has very similar immunological, structural and functional properties to adult antithrombin III. Its presence was demonstrated by; immunodiffusion analysis of a 100-fold concentrate of culture medium, which produced a single precipitin line of identity with adult and 1-day-old hatchling plasma antithrombin III; immunoprecipitation of a metabolically labelled protein from culture medium, having the same molecular size as adult chicken antithrombin III; conversion of antithrombin activity in culture medium to a faster acting thrombin inhibitory activity in the presence of heparin. Antithrombin III antigen levels were increased 3- to 4-fold in the presence of dexamethasone (2 nM) during a 3-day culture period. Plasma antithrombin III antigen levels from unhatched chicks increased from 26 +/- 6 micrograms/ml at 16 days of development to 104 /+- 6 micrograms/ml at 20 days, whereas 1-day-old hatchlings (21 days) had levels similar to that in adults (135 +/- 7 micrograms/ml vs. 143 +/- 24 micrograms/ml). In contrast to immunodiffusion and immunoelectrophoretic analysis of hepatocyte or hatchling plasma antithrombin III, which showed lines of identity with adult antithrombin III, 16- and 20-day-old embryonic plasma antithrombin III yielded lines of partial identity and migrated less anodally than adult antithrombin III. Consistent with this finding, embryonic plasma antithrombin III had no sialic acid (less than 0.01 residue/mol) in contrast with the adult form (3.5 residues/mol). These studies show that the increase in adult antigen levels and sialation of antithrombin III occurs rapidly after hatchling, suggesting developmental changes in expression at the transcriptional and translational levels in addition to post-translational carbohydrate processing.