Fibronectin synthesis by human tubular epithelial cells in culture: effects of PDGF and TGF-beta on synthesis and splicing

BACKGROUND

Enhanced synthesis of extracellular matrix proteins including fibronectin (FN) is associated with the development of sclerosis. In this context we studied FN synthesis by tubular epithelial cells in response to transforming growth factor-beta (TGF-beta) and platelet-derived growth factor (PDGF).

METHODS

FN protein synthesis by human tubular epithelial cells in culture (TEC) was measured by biosynthetic labeling and ELISA. Splicing of FN was assessed by RT-PCR and by Northern blotting.

RESULTS

Cultivated TEC synthesized and released FN, the majority of which was deposited as an unsoluble protein and a minor portion (10 to 15%) was released into the supernatant. TGF-beta and, to a lesser degree, PDGF, up-regulated FN synthesis. All three FN splice variants (EDA, EDB, and IIICS) were produced. PDGF did not influence the splicing. TGF-beta preferentially up-regulated the EDA splice variant, but had no effect on the splicing of the other domains.

CONCLUSIONS

PDGF and TGF-beta both up-regulate FN synthesis of TEC. TGF-beta, but not PDGF, also changed the quality of the de novo synthesized FN, and thus has a different role in the development of sclerosis.

Autoantibodies to polymorphonuclear neutrophil elastase do not inhibit but enhance elastase activity

Polymorphonuclear neutrophils (PMNs) of patients with active Wegener's granulomatosis and PMN activated in vitro express elastase on their surface as detected by autoantibodies derived from patients with ANCA-positive vasculitis or chronic staphylococcus infections. The PMN-associated elastase was enzymatically active. By affinity-purified autoantibodies to elastase, the enzymatic activity was further enhanced as measured either by a chromogenic peptide or by elastin as substrate. Antibodies to human elastase from mouse or from sheep also enhanced elastase activity, whereas unrelated immunoglobulins had no effect. Taken together, our data indicate that autoantibodies to elastase are not inhibitory but upregulate the elastase activity and thereby might contribute to tissue damage.

Synovial fibroblasts as target cells for staphylococcal enterotoxin-induced T-cell cytotoxicity

Rheumatoid arthritis (RA) is a chronic autoimmune disease of unknown aetiology. Recently, superantigens have been implied in the pathogenesis of RA. Superantigens activate a large fraction of T cells leading to the production of cytokines and proliferation. In addition, superantigens direct cellular cytotoxicity towards major histocompatibility complex (MHC) class II-expressing cells. There is now increasing evidence that cytotoxic T cells may be involved in the pathogenesis of RA. In the inflamed synovia class II-positive synovial fibroblasts (SFC) are found. In the present study it was tested whether MHC class II-positive SFC serve as target cells for superantigen-induced cellular cytotoxicity. SFC were stimulated with interferon-gamma to express class II antigens, then they were cultivated in the presence of CD4-positive T cells with or without staphylococcal enterotoxins (SE). Cytotoxicity of T cells was measured as release of lactate dehydrogenase from SFC. Specific cytotoxicity was only found in the presence of class II-positive SFC depending on the dose of SE. Maximum lysis was seen after 20 hr. T-cell cytotoxicity was inhibited by antibodies to MHC class II antigens. The data suggest that class II-positive SFC not only function as accessory cells for SE-mediated T-cell proliferation and interleukin-2 production but may also be the targets of superantigen-mediated cellular cytotoxicity.

Tubular epithelial cells as accessory cells for superantigen-induced T cell activation

In various inflammatory kidney diseases, tubular epithelial cells (TEC) express major histocompatibility complex class II antigens. To assess whether they might have the capacity to directly activate T cells, human TEC in culture were treated with gamma interferon to induce class II expression. TEC were then cocultivated with staphylococcus enterotoxin and cloned T cells or highly purified peripheral T cells. After 1-2 days, release of interleukin 2 and of gamma interferon was seen; after 3-5 days T cell proliferation occurred. The proliferation could be inhibited by antibodies to class II antigens or by antibodies to ICAM-1; the latter is also expressed on TEC in inflammatory processes and on TEC in culture as well. In conclusion, human TEC might function as accessory cells for T cell activation and might support T cell dependent immune response.

Activation of human neutrophils after contact with cellulose-based haemodialysis membranes: intracellular calcium signalling in single cells

PURPOSE OF STUDY

In vitro contact of human leukocytes with cellulose-based dialysis membranes under complement-independent conditions results in activation of various leukocyte functions. To analyse signals involved in the mechanism of cell activation, we measured changes in cytosolic free calcium ([Ca2+]i) in individual human blood neutrophils (PMN) upon contact with flat sheet haemodialysis membranes.

RESULTS

By confocal laser-scanning microscopy (CLSM), changes in [Ca2+]i were monitored in Fluo-3-labelled cells up to 10 min after contact with a regenerated cellulose (RC) membrane. Multiple [Ca2+]i transients were observed for cells in contact with RC; biostochastic analysis showed that up to 67% of the PMN responded with a high increase in [Ca2+]i, the rest were low- or non-responding cells. After contact with the new synthetic polycarbonate-polyether (PC-PE) membrane only non-responding cells were seen, indicating reduced cellular contact activation. The increase in [Ca2+]i of cells on RC could be inhibited by 5mM L-fucose. This monosaccharide was recently found to be present in cellulose-based polymers in picomolar concentrations.

CONCLUSIONS

The data supports the hypothesis that dialysis-membrane-associated L-fucose residues participate in complement-independent leukocyte activation during haemodialysis therapy.

Expression of the 14 kDa galactose-binding protein, galectin-1, on human tubular epithelial cells

By reverse phase PCR and Northern blotting, RNA of the 14 kDa galactose-binding protein (galectin-1) could be identified in primary cultures of human tubular epithelial cells. To assess protein synthesis and the possible function of galectin-1 on TEC, the cellular proteins were biosyntheticically labeled with [34S]-methionine and absorbed to immobilized laminin. Multiple radiolabeled proteins were eluted, a strong band in the area of 14 kDa was seen, coinciding with the galectin-1 band as identified by Western blotting. Surface expression of galectin-1 was seen by cytofluorometry with two different polyclonal antibodies to galectin-1. These data are in line with the finding that tubular epithelial cells adhere to laminin, partly in a Ca(2+)-independent manner.

Antibodies to neutrophil elastase: a study in patients with vasculitis

Whether antibodies to elastase (EL) exist in autoimmune disease is controversial, due in part to inadequate methods used to determine antibody titers. We have developed a highly sensitive and specific enzyme-linked immunosorbent assay, using immobilized EL and mouse monoclonal antibodies for standardization. The specificity of the enzyme-linked immunosorbent assay was confirmed by absorption studies and Western blot analysis. Using this enzyme-linked immunosorbent assay, antibodies to EL were found in antineutrophil cytoplasmic antibody-positive vasculitis patients to a higher degree than reported in the literature (in eight of 108 patients with Wegener's granulomatosis and in 15 of 78 patients with microscopic polyangiitis). Patients with Wegener's granulomatosis or microscopic polyangiitis and antibodies to EL had significantly more severe renal involvement, as indicated by the higher frequency of dialysis dependency. Also in contrast to reported data, antibodies to EL were found less frequently in patients with systemic lupus erythematosus (nine of 64 patients). Binding of systemic lupus erythematosus sera to uncoated plates, giving a nonspecific reaction, was seen quite frequently, which might explain the discrepancy.

Interaction of transforming growth factor beta 1 with human glomerular epithelial cells in culture: opposite effects on synthesis of matrix proteins and on urokinase plasminogen activator

The effect of transforming growth factor-beta (TGF-beta) was analyzed on the synthesis of fibronectin, collagen type IV, and urokinase plasminogen activator in human glomerular epithelial cells in culture. An increase in the abundance of specific mRNA was found for collagen type IV and fibronectin. Fibronectin protein synthesis was also increased in TGF-beta treated cells; most of the de novo synthesized fibronectin was found as an unsoluble protein associated with extracellular matrix. In the same cells the amount of plasminogen activator mRNA was found leading also to a decreased surface expression of urokinase plasminogen activator. The data support the concept that by upregulating matrix protein synthesis and downregulating the plasminogen activator system, TGF-beta favors the development of sclerosis.

Role of the complement membrane attack complex (C5b-9) in mediating experimental mesangioproliferative glomerulonephritis

Previous studies have demonstrated that most pathologic changes in the antithymocyte serum (ATS) model of mesangioproliferative glomerulonephritis are complement-dependent. These include mesangiolysis, glomerular platelet infiltration, mesangial cell proliferation, mesangial cell production of growth factors and phenotypic change to express alpha-actin, glomerular macrophage infiltrate, mesangial matrix expansion, and proteinuria. The mechanism by which complement mediates these effects has not been defined. Because neutrophils do not participate in the ATS model, we hypothesized that the complement effects observed are consequent to glomerular cell insertion of the C5b-9 membrane attack complex of complement. This hypothesis was tested utilizing PVG rats which exhibit an absence of C6 inherited in an autosomal recessive pattern. C6 deficient (C-) PVG rat serum activated by zymosan produced normal amounts of C5a compared to normocomplementemic (C+) PVG rat controls but no C5b-9. When ATS was induced, C- PVG rats had a significant and marked reduction in mesangiolysis, platelet infiltration, mesangial cell proliferation, alpha-actin expression, macrophage infiltration, collagen IV deposition, and proteinuria compared to C+ controls. The reduction in each of these parameters was comparable to that achieved by systemic complement depletion of C+ PVG rats with cobra venom factor. These findings establish the role of C5b-9 in mediating each of the complement-dependent features of the ATS model and indicate that C5b-9 accounts for all of the complement-mediated effects observed. This study provides the first documentation of a functional role for C5b-9 in mediating a non-membranous inflammatory type of glomerular injury in vivo.

Fibronectin modulates interleukin 6 and fibronectin synthesis of human glomerular mesangial cells in culture

In this paper we report that fibronectin (FN) and its proteolytic 120-kD fragment regulate synthesis and secretion of interleukin 6 (IL-6) and of FN by human glomerular mesangial cells. While intact FN and a fragment derived from the heparin-binding domain had no effect on IL-6 secretion, the 120-kD FN fragment containing the cell attachment site stimulated secretion by 40-fold. The same FN fragment reduced FN secretion and the steady state mRNA level by 80%. The intact FN showed only a weak inhibitory effect (+/- 30%); the 30-kD fragment containing the heparin-binding domain had no effect. The effects of the 120-kD FN were inhibited by the peptide RGDS, implying participation of the cell attachment site in signal transduction. An antibody to the alpha-chain of VLA-3 mimicked the effect of the 120-kD FN, whereas an antibody to the alpha-chain of VLA-5 was partly inhibitory. Taken together, the data suggest that FN by interacting with its receptors differentially regulates the protein synthesis of glomerular mesangial cells, promoting IL-6 secretion and inhibiting FN synthesis.

Fibronectin synthesis in tubular epithelial cells: up-regulation of the EDA splice variant by transforming growth factor beta

The influence of transforming growth factor beta 1 (TGF-beta 1) and of dexamethasone on fibronectin (FN) synthesis of human renal tubular epithelial cells in culture (TEC) was studied. Cocultivation with TGF-beta 1 increased the steady state level of FN RNA within 24 to 48 hours. By PCR and Northern blotting it was found that the EDA splice variant of FN was preferentially up-regulated. To quantitate FN protein synthesis, cells were cultivated in the presence of [35S]-methionine and FN was isolated from the cell supernatants, and the cell lysates by adsorption to gelatin-sepharose. In TGF-beta 1 treated cells, a small increase of FN in the cell supernatants was seen (1.7-fold), and a more prominent increase in the cell lysates (4.5-fold). The FN content of the extracellular matrix was also increased in TGF-beta 1 treated cells. Most of the de novo synthesized FN was identified as the EDA-variant of FN. As a further stimulus, dexamethasone was used. Again, an increase of FN-specific mRNA was seen as well as an increased FN protein synthesis. The ratio between FN and EDA-FN, however, was not altered when compared to untreated cells. Thus, an increase in EDA-FN synthesis is obviously stimulus dependent.

Comparative phenotypic analysis of lymph node cells in mice after infection or vaccination with normal or ultraviolet-attenuated cercariae of Schistosoma japonicum or S. mansoni

Mice were infected with 200 untreated or vaccinated with 500 ultraviolet-attenuated cercariae of either Schistosoma japonicum or S. mansoni. For three weeks, cell numbers in axillary and mediastinal lymphnodes were counted and cell populations typed by cytofluorometry. In the axillary lymphnodes, numbers of B-cells and CD3+CD4+ T-cells but not CD3+CD8+ T-cells increased. Following vaccination with either species, parasite migration was apparently delayed in the skin and interrupted at the lungs, the lymphnodes gained weight, and cell numbers of axillary lymph nodes increased more than after infection. In mediastinal lymphnodes, only immunization with S. japonicum but not S. mansoni cercariae led to an increase of CD3+CD4+ T-cells. Following infection, both schistosome species induced higher CD3+CD4+, but not CD3+CD8+ T-cells in mediastinal nodes, and the peak was earlier with S. japonicum (about seven days after infection) than with S. mansoni (about 10 days). In analogy to T-cell observations by others using a gamma-attenuated cercarial vaccine in S. mansoni, the present results suggest that CD3+CD4+ cells also play a role in the ultraviolet-attenuated vaccine against S. japonicum.

Synovial fibroblasts as accessory cells for staphylococcal enterotoxin-mediated T-cell activation

Rheumatoid arthritis (RA) is thought to be the result of T-cell-mediated autoimmune phenomena. So far, a critical autoantigen has not been identified. Recently, superantigens have been implied in the pathogenesis of RA. In the present study it was tested whether major histocompatibility complex (MHC) class II-positive synovial fibroblast cells (SFC) function as superantigen-presenting cells. SFC were stimulated with interferon-gamma (IFN-gamma) to express class II antigens; then they were cultivated in the presence of T cells with or without staphylococcal enterotoxins (SE). T-cell activation was measured as proliferation and interleukin-2 (IL-2) production. Depending on the dose and type of SE, activation of T-cell clones and also of peripheral T cells was seen. T-cell activation was inhibited by antibodies to MHC class II antigens and also by antibodies to intracellular adhesion molecule type-1 (ICAM-1). The data suggest that class II-positive SFC have the capacity to serve as accessory cells for superantigen-mediated T-cell activation. Thus SFC may participate in the propagation of a T-cell dependent immune response.

Matrix protein synthesis by glomerular mesangial cells in culture: effects of transforming growth factor beta (TGF beta) and platelet-derived growth factor (PDGF) on fibronectin and collagen type IV mRNA

The pathogenesis of glomerular scarring is multifactional; recent evidence suggests that transforming growth factor beta (TGF beta), a pleiotropic cicatricial mediator, may promote mesangial sclerosis by enhancing the production of extracellular matrix proteins. We studied the effect of TGF beta 1 and TFG beta 2 on collagen type IV and fibronectin (FN) synthesis in human glomerular mesangial cells in culture (GMC). Two hours after addition of TGF beta, an up to twofold increase in abundance of collagen type IV mRNA was found, which further increased up to fivefold within 24 h. Addition of cycloheximide did not inhibit the TGF beta effect, but caused by itself an up to twofold increase in the abundance of collagen type IV mRNA after 2 h. Together with collagen mRNA, the mRNA for FN and for platelet-derived growth factor (PDGF) was also enhanced. PDGF was found to enhance abundance of the collagen type IV and fibronectin mRNA in GMC. A neutralizing antibody to PDGF or a PDGF-antisense oligonucleotide partly inhibited the TGF beta-induced increase of collagen type IV mRNA, suggesting that TGF beta can affect the collagen type IV synthesis not only directly but also indirectly via the synthesis of PDGF.

Complement component C7 is a plasminogen-binding protein

Ab deposition, whether by reaction with the specific Ag or by preformed immune complexes, is followed by activation and deposition of complement components. Tissue destruction is observed in the Ab- and complement-induced lesions. The proteolytic enzyme plasmin is thought to participate in the Ab- and complement-mediated organ pathology. Plasmin is generated from plasma-derived plasminogen by cell-derived plasminogen activators (PAs). Two types of PAs are known, urokinase-type PA (uPA) and tissue-type PA (tPA). We investigated whether the PA system and the complement system can interact to promote local plasmin generation. Among the terminal complement components C5b6, C7, C8, and C9, the nonenzymatic component C7 is a plasminogen-binding protein. Radioligand binding studies revealed that the isolated component, as well as C7 after its incorporation into the terminal complement complex C5b-9, can bind plasminogen. Binding was inhibited by the lysine analogues 6-aminohexanoic acid and tranexamic acid, implicating the lysine binding sites of plasminogen into the binding interaction. tPA-mediated plasminogen activation was enhanced in the presence of C7. Based on these findings, an interaction is proposed between the complement system and the plasminogen activator system; a mechanism that may focus plasmin activity to structures that have been tagged by Ab and complement deposition.

Complement component C7 is a plasminogen-binding protein

Ab deposition, whether by reaction with the specific Ag or by preformed immune complexes, is followed by activation and deposition of complement components. Tissue destruction is observed in the Ab- and complement-induced lesions. The proteolytic enzyme plasmin is thought to participate in the Ab- and complement-mediated organ pathology. Plasmin is generated from plasma-derived plasminogen by cell-derived plasminogen activators (PAs). Two types of PAs are known, urokinase-type PA (uPA) and tissue-type PA (tPA). We investigated whether the PA system and the complement system can interact to promote local plasmin generation. Among the terminal complement components C5b6, C7, C8, and C9, the nonenzymatic component C7 is a plasminogen-binding protein. Radioligand binding studies revealed that the isolated component, as well as C7 after its incorporation into the terminal complement complex C5b-9, can bind plasminogen. Binding was inhibited by the lysine analogues 6-aminohexanoic acid and tranexamic acid, implicating the lysine binding sites of plasminogen into the binding interaction. tPA-mediated plasminogen activation was enhanced in the presence of C7. Based on these findings, an interaction is proposed between the complement system and the plasminogen activator system; a mechanism that may focus plasmin activity to structures that have been tagged by Ab and complement deposition.

Human glomerular mesangial cells express CD16 and may be stimulated via this receptor

CD16, a low affinity receptor for IgG, was found on cultured human glomerular mesangial cells (GMC) by Western blot analysis, cell ELISA and in situ hybridization. To characterize the molecule in more detail, reverse polymerase chain reaction was performed and the PCR products were analyzed. From sequence analysis and from hybridization experiments with oligonucleotides specific for either the transmembrane form or the glycosylphosphatidylinositol anchored form it was found that GMC-CD16 was similar to NK-CD16. This indicates that GMC express the transmembrane form of CD16. Comparison between nonstimulated GMC and GMC stimulated by aggregated gammaglobulin revealed no qualitative or quantitative difference in the expression of CD16. Incubation of GMC with aggregated gammaglobulin or with monoclonal antibodies to CD16 was followed by a time and dose dependent release of interleukin-6, suggesting that signals were transmitted by CD16. The occupancy of CD16 by immune complexes that may be deposited in various forms of glomerulonephritis might contribute to the perpetuation of inflammatory processes in the kidney.

Expression of the complement regulator factor C8 binding protein on human glomerular cells protects them from complement-mediated killing

The complement-regulatory factor C8 binding protein (C8bp) was first identified on human erythrocyte membranes by its affinity for the complement component C8 and its ability to inhibit lysis by homologous complement. Cultured human glomerular mesangial or epithelial cells (GEC) expressed C8bp on the cell surface and in the cytoplasm. Following stimulation of the glomerular cells with interleukin 1 beta, C5b-9 or with endotoxin, a transient, protein synthesis-independent increase in C8bp surface expression was seen. Blocking of C8bp function with F(ab)2 fragment of an antibody to C8bp rendered GEC susceptible to complement-mediated killing, indicating that C8bp contributes to the cellular defense against complement attack.

Induction of matrix protein synthesis in human glomerular mesangial cells by the terminal complement complex

Exposure of human glomerular mesangial cells (GMC) in culture to sublytic doses of the terminal complement proteins C5b-8 and C5b-9 caused a transient increase in abundance of mRNA specific for collagen type IV and fibronectin; mRNA of laminin was not affected. Since C5b-9 is found deposited in inflamed or sclerotic areas we propose that stimulation of matrix protein synthesis by C5b-9 might contribute to the development of glomerular sclerosis.

Bioincompatibility--perspectives in 1993

Bioincompatibility reactions related to the non-physiology of the procedure have plagued dialysis from its early days. Although the problem is certainly multifactorial, the present overview selectively focuses on some aspects of activation of late complement (C) components, the importance of which may have been underappreciated in the past. Dialysis patients are poised for intense C activation because of cumulation of the low molecular weight factor D, an intrinsically active serine esterase which is not inhibited by any known endogenous inhibitor and catalyzes an early step in the alternative pathway. C activation reflects the net balance between activation and inhibition, the latter particularly via factor H binding. Dialyzer membrane characteristics that are related to factor H binding and regulation of initial activation steps include not only membrane surface chemistry but also its microdomain structure. Kinetic studies of the generation of the terminal complement complex (TCC) suggest ongoing generation throughout the duration of a dialysis session (in contrast to the transient release of C-derived anaphylatoxins). Potential consequences of TCC generation include amplification of the non-C-dependent cell activation signals through L-fucose-dependent steps. Efforts to reduce TCC generation by membrane engineering, for example, end group derivatization and optimization of microdomain structure, open perspectives for the development of more biocompatible membranes.

Chemotaxis of polymorphonuclear neutrophils (PMN) in patients suffering from recurrent infection

PMN function was tested in patients suffering from recurrent infections. In 65 out of 240 patients lack of oxygen radical production or reduced chemotactic activity was found. In most cases the reduction was transient and associated with clinical impairments of the patients. Only a few patients had primary cellular defects. In one of those patients the expression of beta 2 integrins was reduced, while PMN of the other patients expressed beta 2 integrins normally. Thus, cellular defects other than the reduced expression of beta 2 integrins might also result in impaired chemotactic activity.

Deafness, complement deficiencies and immunoglobulin status in patients with meningococcal diseases due to uncommon serogroups

The prevalence of deafness and complement deficiencies in association with meningococcal disease caused by uncommon serogroups of meningococci was studied in 30 patients (Group A) and 30 controls with Serogroup B disease (Group B). In Group A 8 patients (26.6%) had hearing impairment in contrast to only 1 patient (3.3%) in Group B (P < 0.01). Complement deficiency was detected in 8 patients (26.6%) of Group A whereas none of the Group B patients showed a defect in the complement system (P < 0.01). Association between complement deficiencies and meningococcal disease was detected for Serogroups Y (n = 5; 16.6%) and W135 (n = 3; 10.0%). Localization of the defects revealed only complement deficiencies of the classical pathway (C8-beta or C7 defects). The levels of Ig and IgG subclasses were found to be within the normal range for all patients. Our results suggest that meningococcal diseases caused by uncommon serogroups are more often associated with deafness and late complement component defects.

Stimulation of mononuclear cells by contact with cuprophan membranes: further increase of beta 2-microglobulin synthesis by activated late complement components

Contact of mononuclear cells (MNC) with cuprophan membranes in vitro causes an increase in beta 2-microglobulin (beta 2m) synthesis. Since in vivo the dialyzer membrane is rapidly coated with plasma proteins, contact activation of MNC was tested in the presence of normal human serum (NHS). After contact with cuprophan, deposition of C5b-9 on the cells was seen, followed by an increase in beta 2m synthesis and cytokine release, exceeding that seen after contact activation in the absence of serum. Inactivated serum or serum deficient in C8 did not increase beta 2m production, indicating that the additional activation was due to complement C5b-9. The results suggest that there are two cuprophan-related mechanisms of cell activation: one by contact of cells with the membrane, the other by the complement activation products. Both might synergistically contribute to an increased beta 2m synthesis in hemodialysis patients.

Interaction of the terminal complement components C5b-9 with synovial fibroblasts: binding to the membrane surface leads to increased levels in collagenase-specific mRNA

The late complement components, apart from their lytic function, are known to trigger the release of various proinflammatory substances from different types of nucleated cells. In the present study, the interaction of C5b-9 with synovial fibroblast cells (SFC) was examined. It was found that incubation of SFC with activated complement components resulted in binding of C5b-9 to the cell membrane; subsequently an increase in abundance of collagenase-specific mRNA was seen, as assessed by Northern blotting. When C8-deficient serum was used as source of complement neither binding of C5b-9 nor an increase in collagenase-specific mRNA could be detected. These findings suggest that C5b-9, which might be generated during rheumatoid inflammation, may contribute to chronic joint destruction by triggering collagenolytic activity.