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

Shaping Up the Tumor Microenvironment With Cellular Fibronectin

Normal tissue homeostasis and architecture restrain tumor growth. Thus, for a tumor to develop and spread, malignant cells must overcome growth-repressive inputs from surrounding tissue and escape immune surveillance mechanisms that curb cancer progression. This is achieved by promoting the conversion of a physiological microenvironment to a pro-tumoral state and it requires a constant dialog between malignant cells and ostensibly normal cells of adjacent tissue. Pro-tumoral reprogramming of the stroma is accompanied by an upregulation of certain extracellular matrix (ECM) proteins and their cognate receptors. Fibronectin (FN) is one such component of the tumor matrisome. This large multidomain glycoprotein dimer expressed over a wide range of human cancers is assembled by cell-driven forces into a fibrillar array that provides an obligate scaffold for the deposition of other matrix proteins and binding sites for functionalization by soluble factors in the tumor microenvironment. Encoded by a single gene, FN regulates the proliferation, motile behavior and fate of multiple cell types, largely through mechanisms that involve integrin-mediated signaling. These processes are coordinated by distinct isoforms of FN, collectively known as cellular FN (as opposed to circulating plasma FN) that arise through alternative splicing of the FN1 gene. Cellular FN isoforms differ in their solubility, receptor binding ability and spatiotemporal expression, and functions that have yet to be fully defined. FN induction at tumor sites constitutes an important step in the acquisition of biological capabilities required for several cancer hallmarks such as sustaining proliferative signaling, promoting angiogenesis, facilitating invasion and metastasis, modulating growth suppressor activity and regulating anti-tumoral immunity. In this review, we will first provide an overview of ECM reprogramming through tumor-stroma crosstalk, then focus on the role of cellular FN in tumor progression with respect to these hallmarks. Last, we will discuss the impact of dysregulated ECM on clinical efficacy of classical (radio-/chemo-) therapies and emerging treatments that target immune checkpoints and explore how our expanding knowledge of the tumor ECM and the central role of FN can be leveraged for therapeutic benefit.

Receptor-independent modulation of TGF-β-induced pro-fibrotic pathways by relaxin-2 in human primary tubular epithelial cells

Renal tubular epithelial cells actively contribute to the development of renal fibrosis and may be targeted by anti-fibrotic drugs. Relaxin-2 (RLX2) applied as recombinant protein is suggested to be renoprotective. Therefore, we investigated whether human primary tubular epithelial cells (hPTEC) obtained from various donors were target cells for the anti-fibrotic actions of RLX2. Treatment of hPTEC with RLX2 reduced the TGF-β1-induced secretion of the pro-fibrotic factor CTGF (connective tissue growth factor) and inhibited fibronectin synthesis and secretion. Furthermore, metalloproteinase MMP2 secretion was increased, with no effect on MMP9. Considerable differences were observed between hPTEC obtained from different donors. Therefore, expression of the relaxin family peptide receptor RXFP1, the major mediator of renal RLX2 effects, was analyzed. A validated antibody detected a double band of 80-90 kDa in cellular homogenates by Western blotting. Expression of the detected protein was not altered by incubation with TGF-β1 and RLX2-induced modulation of CTGF expression did not correlate with the putative receptor expression. Therefore, relaxin family receptors RXFP1-4 were assessed by RNA-seq analysis. No evidence was found for mRNA expression of any of these receptors in several hPTEC preparations. Lack of RXFP1 mRNA was confirmed by qPCR using mRNA obtained from THP-1 cells as positive control. Our data thus provide evidence for primary renal human tubular epithelial cells as targets for the anti-fibrotic actions of RLX2. However, anti-fibrotic effects were observed at micromolar concentrations of RLX2 and shown to be independent of RXFP1 expression.

TGF-β induces oncofetal fibronectin that, in turn, modulates TGF-β superfamily signaling in endothelial cells

Gene splicing profiles are frequently altered in cancer, and the splice variants of fibronectin (FN) that contain the extra-domains A (EDA) or B (EDB), referred to as EDA+FN or EDB+FN, are highly upregulated in tumor vasculature. Transforming growth factor β (TGF-β) signaling has been attributed a pivotal role in glioblastoma, with TGF-β promoting angiogenesis and vessel remodeling. By using immunohistochemistry staining, we observed that the oncofetal FN isoforms EDA+FN and EDB+FN are expressed in glioblastoma vasculature. Ex vivo single-cell gene expression profiling of tumors by using CD31 and α-smooth muscle actin (αSMA) as markers for endothelial cells, and pericytes and vascular smooth muscle cells (VSMCs), respectively, confirmed the predominant expression of FN, EDA+FN and EDB+FN in the vascular compartment of glioblastoma. Specifically, within the CD31-positive cell population, we identified a positive correlation between the expression of EDA+FN and EDB+FN, and of molecules associated with TGF-β signaling. Further, TGF-β induced EDA+FN and EDB+FN in human cerebral microvascular endothelial cells and glioblastoma-derived endothelial cells in a SMAD3- and SMAD4-dependent manner. In turn, we found that FN modulated TGF-β superfamily signaling in endothelial cells via the EDA and EDB, pointing towards a bidirectional influence of oncofetal FN and TGF-β superfamily signaling.

Deletion of β1-integrin in collecting duct principal cells leads to tubular injury and renal medullary fibrosis

The renal collecting duct (CD) contains two major cell types, intercalated (ICs) and principal cells (PCs). A previous report showed that deletion of β1-integrin in the entire renal CD causes defective CD morphogenesis resulting in kidney dysfunction. However, subsequent deletion of β1-integrin specifically in ICs and PCs, respectively, did not cause any morphological defects in the CDs. The discrepancy between these studies prompts us to reinvestigate the role of β1-integrin in CD cells, specifically in the PCs. We conditionally deleted β1-integrin in mouse CD PCs using a specific aquaporin-2 (AQP2) promoter Cre-LoxP system. The resulting mutant mice, β-1^f/fAQP2-Cre+, had lower body weight, failed to thrive, and died around 8-12 wk. Their CD tubules were dilated, and some of them contained cellular debris. Increased apoptosis and proliferation of PCs were observed in the dilated CDs. Trichrome staining and electron microscopy revealed the presence of peritubular and interstitial fibrosis that is associated with increased production of extracellular matrix proteins including collagen type IV and fibronectin, as detected by immunoblotting. Further analysis revealed a significantly increased expression of transforming growth factor-β (TGF-β)-induced protein, fibronectin, and TGF-β receptor-1 mRNAs and concomitantly increased phosphorylation of SMAD-2 that indicates the activation of the TGF-β signaling pathway. Therefore, our data reveal that normal expression of β1-integrin in PCs is a critical determinant of CD structural and functional integrity and further support the previously reported critical role of β1-integrin in the development and/or maintenance of the CD structure and function.

QiShenYiQi Attenuates Renal Interstitial Fibrosis by Blocking the Activation of β-Catenin

Chronic kidney disease (CKD) is becoming a worldwide problem. However, current treatment options are limited. In the current study we showed that QiShenYiQi (QSYQ), a water-ethanol extract from several Chinese medicines, is a potent inhibitor of renal interstitial fibrosis. QSYQ inhibited transforming growth factor-β1 (TGF-β1)-responsive α-smooth muscle actin (α-SMA), collagen I, and fibronectin up-regulation in obstructive nephropathy and cultured cells. Administration of QSYQ also inhibited the established renal interstitial fibrosis in obstructive nephropathy. Interestingly, QSYQ selectively inhibited TGF-β1-induced β-catenin up-regulation and downstream gene transcription. Taken together, our study suggests that QSYQ selectively inhibits TGF-β1-induced β-catenin up-regulation and might have significant therapeutic potential for the treatment of renal fibrosis.

Alternative Splicing in CKD

Alternative splicing (AS) has emerged in the postgenomic era as one of the main drivers of proteome diversity, with ≥94% of multiexon genes alternatively spliced in humans. AS is therefore one of the main control mechanisms for cell phenotype, and is a process deregulated in disease. Numerous reports describe pathogenic mutations in splice factors, splice sites, or regulatory sequences. Additionally, compared with the physiologic state, disease often associates with an abnormal proportion of splice isoforms (or novel isoforms), without an apparent driver mutation. It is therefore essential to study how AS is regulated in physiology, how it contributes to pathogenesis, and whether we can manipulate faulty splicing for therapeutic advantage. Although the disease most commonly linked to deregulation of AS in several genes is cancer, many reports detail pathogenic splice variants in diseases ranging from neuromuscular disorders to diabetes or cardiomyopathies. A plethora of splice variants have been implicated in CKDs as well. In this review, we describe examples of these CKD-associated splice variants and ideas on how to manipulate them for therapeutic benefit.

The Regulation of TGFβ1 Induced Fibronectin EDA Exon Alternative Splicing in Human Renal Proximal Tubule Epithelial Cells

The EDA+ splice variant of fibronectin (Fn) is an early and important component of the extracellular matrix in renal fibrosis. In this work, we investigate cellular mechanisms of EDA+Fn production in human primary proximal tubule epithelial cells (PTECs). TGFβ1-induced EDA+Fn production was assessed by immunocytochemistry, PCR, and Western blotting. SRp40 knockdown was achieved by siRNA. The role of the PI3 kinase-AKT signalling and splicing regulatory protein SRp40 in the production of EDA+Fn was studied by using the chemical inhibitor LY294002 and siRNA targeted to SRp40 respectively. Interaction between PI3 kinase-AKT signalling and SRp40 were assessed by immunofluorescence and immunoprecipitation. To assess the specificity of SRp40 in regulating the splicing of EDA+ exon, we studied the effect of SRp40 knockdown on TGFβ1 induced splicing of FGF receptor 2. Primary human PTECs expressed EDA+ and EDA- Fn. TGFβ1 treatment resulted in increases in the production and deposition of EDA+ Fn as well as an increase in the ratio of EDA+/EDA- Fn mRNA. The TGFβ1 induced EDA+ production was dependent on PI3 kinase-AKT signalling and SRp40 expression. Immunoprecipitation experiments demonstrated direct binding between AKT and SRp40 with an increase in the amount of SRp40 bound to AKT upon TGFβ1 treatment. TGFβ1 treatment resulted in reduction in the FGF receptor2 IIIb splice variant which was unaffected by SRp40 knockdown. In this work, we have presented the first evidence for the regulation of Fn pre-mRNA splicing by PI3 kinase-AKT signalling and SRp40 in human PTECs. Targeting the splicing of Fn pre-mRNA to skip the EDA exon is an attractive option to combat fibrosis.

Are the Mesothelial-to-Mesenchymal Transition, Sclerotic Peritonitis Syndromes, and Encapsulating Peritoneal Sclerosis Part of the Same Process?

Mesothelial-to-mesenchymal transition (MMT) is an autoregulated physiological process of tissue repair that in uncontrolled conditions, such as peritoneal dialysis (PD), can lead to peritoneal fibrosis. The maximum expression of sclerotic peritoneal syndromes (SPS) is the encapsulating peritoneal sclerosis (EPS) for which no specific treatment exists. The SPS includes a wide range of peritoneal fibrosis that appears progressively and is considered as a reversible process, while EPS does not. EPS is a serious complication of PD characterized by a progressive intra-abdominal inflammatory process that results in bridles and severe fibrous tissue formation which cover and constrict the viscera. Recent studies show that transdifferentiated mesothelial cells isolated from the PD effluent correlate very well with the clinical events such as the number of hemoperitoneum and peritonitis, as well as with PD function (lower ultrafiltration and high Cr-MTC). In addition, in peritoneal biopsies from PD patients, the MMT correlates very well with anatomical changes (fibrosis and angiogenesis). However, the pathway to reach EPS from SPS has not been fully and completely established. Herein, we present important evidence pointing to the MMT that is present in the initial peritoneal fibrosis stages and it is perpetual over time, with at least theoretical possibility that MMT initiated the fibrosing process to reach EPS.

The TGFbeta1-induced fibronectin in human renal proximal tubular epithelial cells is p38 MAP kinase dependent and Smad independent

BACKGROUND/AIM

Transforming growth factor beta 1 (TGFbeta1) is a fibrokine implicated in the progression of renal fibrosis. Following TGFbeta1 receptor activation, a number of signalling pathways are stimulated. This study investigates the role of p38 mitogen-activated protein (MAP) kinase and Smad pathways in the TGFbeta1-induced fibronectin (FN) production.

METHODS

Transformed human proximal tubular epithelial cells of the line HKC were used. Secreted FN was analyzed by enzyme-linked immunosorbent assay and Smad proteins by Western blotting. Chemical inhibitors were used to study the role of p38 MAP kinase and the TGFbeta receptor ALK5. The Smad pathway was studied using a cell line overexpressing Smad7 and small interfering RNAs (siRNA). The FN mRNA expression was assessed by reverse transcription-polymerase chain reaction.

RESULTS

TGFbeta1 produced a significant increase in FN secretion in both HKC and Smad7-HKC cells, and the p38 MAP kinase inhibitor SB202190 markedly reduced this (n = 3, p < 0.05 and p < 0.01). ALK5 inhibition also reduced the TGFbeta1-induced FN (n = 3, p < 0.05). Smad knockdown using the siRNA did not reduce the TGFbeta1-induced FN secretion. TGFbeta1 induced FN mRNA expression in HKC cells, and SB202190 decreased this induction (n = 5, p < 0.05).

CONCLUSIONS

These results suggest that TGFbeta1-induced FN production in HKC cells is p38 MAP kinase dependent and Smad independent. Targeting p38 MAP kinase may be of therapeutic value in renal fibrosis.

Dexamethasone induces connective tissue growth factor expression in renal tubular epithelial cells in a mouse strain-specific manner

Connective tissue growth factor (CTGF), a downstream mediator of transforming growth factor-beta1, mediates mesangial cell/fibroblast proliferation and extracellular matrix production by renal cells. Here, we show that renal tubular epithelial cells from patients with minimal change nephritic syndrome produced CTGF after glucocorticoid treatment. In addition, the glucocorticoid dexamethasone (DEX) increased CTGF mRNA levels in the kidneys of C57B6 but not SJL mice and produced intermediate CTGF mRNA levels in the kidneys of F1 (C57B6 x SJL) mice, midway between the levels found for parental strains. DEX also increased CTGF mRNA levels in cultured tubular epithelial cells derived from C57B6 (mProx24) but not SJL (MCT) mice via transcriptional up-regulation of CTGF mRNA. Transient transfection experiments using luciferase reporter constructs bearing CTGF promoter fragments revealed that the -897- to -628-bp fragment contained DEX-responsive positive regulatory elements, which were active in mProx24 but not MCT cells. Long-term DEX treatment resulted in fibronectin deposition in the kidneys of C57B6 but not SJL mice, and this effect was inhibited by co-administration of CTGF anti-sense oligodeoxynucleotides. Thus, glucocorticoid-induced renal fibrogenesis seems to be influenced by genetic background, with the critical DEX-responsive elements in the -897- to -628-bp region of the CTGF promoter.

Fibronectin on activated T lymphocytes is bound to gangliosides and is present in detergent insoluble microdomains

Fibronectin (FN) is a multifunctional extracellular matrix glycoprotein, which participates in cell migration and signalling to adhering cells. Due to alternative splicing and post-translational modifications, different isoforms of FN are generated by a wide variety of cells. T lymphocytes synthesize a surface-associated isoform of FN, containing the two 'extradomains' EDA and EDB. In the present study, we identified gangliosides within the T-cell membrane as specific binding sites for the N-terminal 30 kDa fragment of FN. When T cells were activated with anti-CD3 coated beads, FN, together with the ganglioside GM1, converged at the contact zone. Moreover, endogenous FN was present in the detergent insoluble microdomain. The function of FN in T cells is still under investigation; however, its presence together with gangliosides at the activation site suggests participation in T-cell signalling.

The use of extracellular matrix probes and extracellular matrix-related probes for assessing diagnosis and prognosis in renal diseases

PURPOSE OF REVIEW

Scarring in the kidney results from excessive local synthesis and exogenous accumulation of extracellular matrix components. Once chronic damage is present in the biopsy, therapeutic intervention for the renal patient encounters severe limitations. It is therefore essential to determine clinical outcome preferably at a time point before the development of overt scarring. Clinical parameters and morphologic alterations in the biopsy are currently used as tools for the diagnosis of the renal disease entity and for assessment of the patient's prognosis. Expression levels of extracellular matrix and matrix-related components may serve as additive and even superior prognostic indicators to conventional parameters. We will elaborate on studies supporting this concept.

RECENT FINDINGS

Several investigators have shown in experimental models for renal disease that extracellular matrix probes and related probes reflect disease progression and predict outcome. In this review, we will provide an update on the most recent studies of human renal biopsies showing that expression of extracellular matrix components, regulators of matrix degradation, and cytokines affecting matrix deposition may be employed for discrimination of diagnostic groups and predicting prognosis.

SUMMARY

Molecular techniques are expected to be used more and more for diagnostic and prognostic purposes in nephrological practice to supplement the histopathological analysis of the renal biopsy. Assessment of expression of matrix molecules, matrix-regulating cytokines, and metalloproteinases in renal kidney biopsies is helpful to distinguish patients who are at risk of developing progressive renal failure from patients who are likely to recover from renal tissue injury by natural remodeling mechanisms.

Transforming growth factor-β1 (TGF-β1) regulates ATDC5 chondrogenic differentiation and fibronectin isoform expression

Regulated splicing of fibronectin (FN) occurs during the mesenchymal to chondrocyte transition and ultimately results in the relative enrichment of an extra domain B (EDB) exon-containing FN isoform with the suggestion that FN isoforms may play a functional role in chondrogenesis. Promotion of chondrogenesis can also be achieved by treatment with transforming growth factor-beta (TGF-beta), which also regulates FN isoform expression. We have examined the effects of TGF-beta treatment on the assumption of the chondrogenic phenotype in the teratoma-derived cell line ATDC5 and tested whether these effects on chondrogenesis are paralleled by appropriate changes in FN isoform expression. ATDC5 cells were maintained in a pre-chondrogenic state and, in this state, treated with 10 ng/ml TGF-beta. The cells started to elaborate a matrix rich in sulfated proteoglycans, such that within the first 12 days of culture, TGF-beta1 treatment appeared to slightly accelerate early acquisition of an Alcian blue-stained matrix, and caused a dose- and time-dependent decrease in collagen type I expression; changes in collagen type II expression were variable. At later times, cells treated with TGF-beta became indistinguishable from those of the controls. Interestingly, TGF-beta treatment caused a significant dose- and time-dependent decrease in the proportion of FN containing the extra domain A (EDA) and the EDB exons. These data suggest that TGF-beta induces the early stages of chondrogenic maturation in this pre-chondrogenic line and that TGF-beta treatment increases expression of FN isoforms that lack the EDA and EDB exons.

Alternatively spliced isoforms of fibronectin in immune-mediated glomerulosclerosis: the role of TGF? and IL-4

Fibronectin (FN) is the main extracellular matrix component in glomerulosclerotic lesions. There are different FN isoforms that result from alternative splicing at the EDA and EDB regions of FN mRNA. Increased inclusion of EDA and EDB, which can be elicited by TGFbeta, may be conducive to the development of glomerulosclerosis (GS). TGFbeta and IL-4 have previously been shown to play a role in the development of GS. In this study, the mRNA splicing patterns for EDA+ and EDB+ fibronectin were investigated in vivo in various experimental sclerotic glomerulopathies, in vitro in rat mesangial cells (MC) that were stimulated by TGFbeta or transfected with IL-4, and in human kidney biopsies with GS from patients with various kidney diseases. Analysis of glomerular FN mRNA demonstrated inclusion of both ED regions in rats with anti-Thy1 nephritis or chronic serum sickness and in mice with anti-GBM glomerulonephritis. Inclusion of both the EDA and EDB regions was associated with glomerular TGFbeta expression. In contrast, in mice with Th2-mediated graft-versus-host disease, a model for lupus nephritis, the FN transcripts included neither the EDA nor the EDB region, and renal TGFbeta expression was absent. Compared to normal MCs in culture, MCs transfected with IL-4 produced lower amounts of FN and demonstrated less EDA inclusion, while MC that had been treated with TGFbeta showed increased production of FN and more EDA inclusion. Renal biopsies from patients with renal diseases, except those taken from patients with lupus nephritis, showed higher TGFbeta levels, higher FN levels, and more EDA inclusion than controls. TGFbeta may be a key player in the development of GS by inducing local FN production and alternative splicing of FN mRNA. In lupus glomerulonephritis, in which the involvement of TGFbeta in GS is less prominent, Th2 cytokines such as IL-4 probably account for increased intrarenal collagen synthesis and subsequent FN accumulation from the circulation. In conclusion, neither alternative FN splicing, nor a high transcription level of TGFbeta, appears to be a general prerequisite for the development of GS.

Mechanism of steroid action in renal epithelial cells

Renal tubular epithelial cells (TEC) are thought to play an active role in tubulointerstitial inflammation. Various immune and non-immune factors activate TEC to produce a variety of cytokines and chemokines, contributing to attraction of inflammatory cells to the kidney. The proinflammatory transcription factor nuclear factor-kappaB (NF-kappaB) appears to be a key player in these responses and tubular expression of NF-kappaB has been demonstrated in vitro and in vivo. Although glucocorticoids are known to inhibit NF-kappaB activation at different levels, the proinflammatory capacity of TEC was not inhibited. In contrast, glucocorticoids seemed to enhance the profibrotic response of TEC, emphasizing the cell-type specific characteristics of glucocorticoid action. We propose that specific inhibition of NF-kappaB activation in TEC might be an attractive strategy for therapeutic intervention in renal inflammation.

Fibronectin expression in proximal tubules from ischemic rat kidneys without reperfusion

The expression of fibronectin (FN), one of the extracellular matrix proteins, was studied in isolated renal proximal tubules in a in vivo rat model of unilateral renal ischemia without reperfusion. FN is involved in cell-extracellular matrix interactions and defective cell-extracellular matrix interactions have been hypothesized to contribute to ischemic renal failure. The expression of FN was investigated by reverse transcription-polymerase chain reaction (RT-PCR), Elisa and Western blot. Isolated proximal tubules from control and post-ischemic rat kidneys were used. ATP, intracellular calcium content, and alkaline phosphatase were also measured to describe the effects associated to 40 min of ischemia. Control tubules expressed FN. Forty minutes of ischemia promoted diminished ATP levels and phosphatase alkaline activity, and increased intracellular calcium in isolated proximal tubules. An increased abundance of FN was observed by ischemic tubules as compared with control tubules. To determine quantitatively the value of FN content, ELISA method was performed. The ischemic tubules also expressed higher amount of FN mRNA. Three amplification products were obtained from both ischemic and control proximal tubular cDNA. The relative amounts of each of the obtained products were the same, strongly suggesting that the augmentation of the FN gene transcription during ischemia is not associated to a modification in the splicing pattern. Moreover, this expression is increased after 40 min of ischemia, not followed by reperfusion.

MCP-1 induces inflammatory activation of human tubular epithelial cells: involvement of the transcription factors, nuclear factor-kappaB and activating protein-1

Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine synthesized by several cell types, e.g., inflammatory cells, such as monocytes, and resident renal cells, such as human tubular epithelial cells (TECs). Besides induction of monocyte recruitment, MCP-1 has been suggested to induce non-leukocytes to produce cytokines and adhesion molecules. Inflammation of the tubulointerstitium is a hallmark of many renal diseases and contributes to progression of renal failure; the purpose therefore of this study was to investigate the influence of MCP-1 on markers of inflammatory activation in human TECs. MCP-1 stimulated interleukin-6 (IL-6) secretion and intercellular adhesion molecule-1 (ICAM-1) synthesis in a time- and dose-dependent manner. In parallel, MCP-1 increased IL-6 and ICAM-1 mRNA expression in human TECs. Pretreatment with pertussis toxin, GF109203X, BAPTA-AM, and pyrrolidine dithiocarbamate inhibited MCP-1-dependent IL-6 and ICAM-1 synthesis, suggesting the involvement of Gi-proteins, protein kinase C, intracellular Ca(2+), and nuclear factor-kappaB (NF-kappaB) in MCP-1 signaling. Using electrophoretic gel mobility shift assay, we observed that MCP-1 stimulated binding activity of NF-kappaB. Binding activity of the activator protein-1 (AP-1), which has been implicated to regulate induction of the IL-6 gene together with NF-kappaB, was also stimulated by MCP-1. In the present experiments, NF-kappaB and AP-1 were involved in the MCP-1-mediated induction of IL-6, as demonstrated by cis element double-stranded (decoy) oligonucleotides (ODN). In contrast to IL-6 release, MCP-1-induced ICAM-1 expression was predominantly dependent on NF-kappaB activation. These results document for the first time that MCP-1 induces an inflammatory response in human TECs. This may be an important new mechanism in the pathogenesis of tubulointerstitial inflammation.

Catecholamines stimulate interleukin-6 synthesis in rat cardiac fibroblasts

Proinflammatory cytokines have been implicated in the pathophysiology of different heart diseases. Recent evidence suggests that interleukin-6 (IL--6) may play a role in mechanisms leading to cardiac hypertrophy. In addition, catecholamines are known to induce cardiac hypertrophy. In the present study, we examined whether cardiac fibroblasts may be a potential source of IL--6 production in the rat heart and whether catecholamines can modulate the IL--6 synthesis. Only a small amount of IL--6 mRNA was detected in unstimulated rat cardiac fibroblasts. However, a 50-fold increase of IL--6 mRNA was found after stimulation with norepinephrine (NE). Addition of carvedilol, a alpha- and beta-adrenergic receptor antagonist, prevented almost completely the NE-induced synthesis of IL--6 mRNA. Phenylephrine, an alpha-adrenergic agonist, and isoproterenol, a beta-adrenergic agonist, also induced an increase in IL--6. However, the stimulation via beta-receptors led to a more pronounced elevation. These data show that NE increases IL--6 expression in rat cardiac fibroblasts and that IL--6 may play an important autocrine/paracrine role in cardiac disease states associated with hypertrophy.

Expression of fibronectin splice variants in the postischemic rat kidney

Using an in vivo rat model of unilateral renal ischemia, we previously showed that the expression and distribution of fibronectin (FN), a major glycoprotein of plasma and the extracellular matrix, dramatically changes in response to ischemia-reperfusion. In the distal nephron in particular, FN accumulates in tubular lumens, where it may contribute to obstruction. In the present study, we examine whether the tubular FN is the plasma or cellular form, each of which is produced by alternative splicing of a single gene transcript. We demonstrate that FN in tubular lumens does not contain the extra type III A (EIIIA) and/or the extra type III B (EIIIB) region, both of which are unique to cellular FN. It does, however, contain the V95 region, which in the rat is a component of FNs in both plasma and the extracellular matrix. Expression of FN containing EIIIA increases dramatically in the renal interstitium after ischemic injury and continues to be produced at high levels 6 wk later. V95-containing FN also increases in the interstitial space, albeit more slowly and at lower levels than FN containing EIIIA; it also persists 6 wk later. FN containing the EIIIB region is not expressed in the injured kidney. The presence of V95 but not the EIIIA or EIIIB regions of FN in tubular lumens identifies the origin of FN in this location as the plasma; tubular FN is ultimately voided in the urine. The data indicate that both plasma and cellular FNs containing the V95 and/or EIIIA regions may contribute to the pathogenesis of acute renal failure and to the repair of the injured kidney.

Distribution of fibronectin isoforms in human renal disease

Fibronectin (FN) is an extracellular matrix component which appears in different isoforms, due to alternative mRNA splicing of the ED-A, ED-B, and IIICS regions, and subsequent post-translational modifications. The FN isoforms, some of which occur specifically during fetal development and in fibrogenic diseases, have been reported to play a role in various biological functions, such as regulation of the matrix assembly, adhesion, and proliferation. The contribution of these FN isoforms to the pathogenesis of chronic renal diseases, which are also fibrogenic disorders, is not well known. This study therefore examined the distribution of FN isoforms in renal diseases by immunohistochemistry, with a panel of isoform-specific monoclonal antibodies (MAbs), applied to 63 abnormal renal biopsies and ten normal controls. Normal kidneys contained total FN (MAb IST4) both in the mesangial and in the interstitial extracellular matrix (ECM), but only traces of ED-A-positive FN (MAb IST9), and no ED-B-positive FN (MAb BC1) or oncofetal FN (MAb FDC6) was found in normal renal tissue. All patients with renal disease demonstrated increased total FN staining of the interstitium and the mesangium. Periglomerular fibrotic lesions and fibrous crescents showed massive accumulation of total FN, whereas the amount of total FN in the ECM of obsolescent glomeruli was decreased, compared with that in normal mesangial ECM. Oncofetal (FDC6), EDB-negative (MAb IST6), ED-A-positive, and ED-B-positive FN isoforms were found in glomerular ECM accumulations and in fibrous crescents. Tubulointerstitial fibrotic lesions predominantly contained the ED-A-positive FN isoform, whereas in globally sclerotic glomeruli, predominantly ED-B-positive FN was observed. The expression of FN isoforms was similar in all renal diseases studied. These results show that in various renal diseases, oncofetal (FDC6) FN and ED-A- and ED-B-positive isoforms of FN accumulate at locations of chronic lesions, independently of the aetiology of the disease. The deposition of these isoforms in human renal tissue may play a role in the modulation of the immune response by attracting monocytes and lymphocytes to the injured kidney. Furthermore, because the ED-B-positive FN isoform is highly susceptible to proteolytic degradation, its accumulation may play a role in scar formation and tissue repair. ED-B-positive FN forms a temporary scaffold supporting the cells, which can easily be cleared by proteolytic degradation once new tissue has been produced at the site of injury.

The terminal complement complex C5b-9 stimulates interleukin-6 production in human smooth muscle cells through activation of transcription factors NF-kappa B and AP-1

Activation of the complement system plays an important role in the pathogenesis of atherosclerosis. The proinflammatory cytokine interleukin (IL)-6 is potentially involved in the progression of the disease. We therefore investigated whether the terminal complement complex C5b-9 affects IL-6 production from vascular smooth-muscle cells (VSMC) and set out to determine the underlying signal transduction pathway. Stimulation of human VSMC with C5b-9 resulted in an increase of IL-6 transcript and production of IL-6 protein. Pretreatment with pertussis toxin or pyrrolidine dithiocarbamate inhibited complement-dependent IL-6 mRNA expression and IL-6 release, suggesting the involvement of Gi-proteins and nuclear factor-kB (NF-kB). C5b-9 also induced formation of reactive oxygen species, which, along with IL-6 release, was inhibited by the antioxidant N-acetylcysteine. C5b-9 activated the redox-sensitive transcription factors NF-kB and activator protein-1 (AP-1), which were both involved in the induction of IL-6 by C5b-9, as demonstrated by cis element double-stranded (decoy) oligonucleotides (ODN). The results demonstrate that activation of the complement system induces IL-6 release from human VSMC by a Gi-dependent pathway involving the generation of oxidative stressand the activation of the redox sensitive transcription factors NF-kB and AP-1. Our data support a new mechanism for the proatherogenic effect of the terminal complement complex.

Fibronectin synthesis by activated T lymphocytes: up-regulation of a surface-associated isoform with signalling function

Fibronectin (FN) is a major constituent of the extracellular matrix. We now provide evidence for a surface-associated isoform of FN that is synthesized by T cells upon activation. The T-cell-derived FN has an unusual splice pattern: an additional domain, EDB, is produced whereas sequences within another domain, IIICS, are spliced out. CS1, the binding domain for very late antigen-4 (VLA-4), however, is still generated. To study the potential function of surface-associated FN its synthesis was down-regulated by an antisense oligonucleotide, then proliferation of T cells was induced by cross-linked anti-CD3. Proliferation was reduced as was expression of CD25. Moreover, when T cells were cultured in high density, the synthetic peptide QILDVPST, corresponding to CS1, inhibited proliferation, as did antibodies to VLA-4. We propose that surface-associated FN is a ligand for VLA-4, which by binding to VLA-4 on an adjacent cell, provides a costimulatory signal, thus sustaining T-cell proliferation.

Early treatment with corticosteroids ameliorates proteinuria, proliferative lesions, and mesangial phenotypic modulation in adult diffuse proliferative IgA nephropathy

Diffuse proliferative immunoglobulin A (IgA) nephropathy has the potential risk for end-stage renal disease. However, treatment of IgA nephropathy has not been well established. To determine whether early treatment with corticosteroids ameliorates the proliferative lesions of diffuse proliferative IgA nephropathy, we conducted a prospective, randomized, controlled trial. Inclusion criteria were as follows: duration of abnormal urinalysis results less than 36 months, proteinuria less than 1.5 g/d of protein, serum creatinine level less than 1.5 mg/dL, and mesangial cell proliferation or matrix accumulation involving more than 50% of glomeruli. Twenty-one patients were randomly assigned to two groups: the corticosteroid group and the antiplatelet group. After 1 year of treatment, repeated renal biopsy was performed in 19 patients. We evaluated glomerular filtration rate, blood pressure, proteinuria, and histological parameters, including light microscopic findings and staining of alpha-smooth muscle actin (alphaSMA), as a marker of myofibroblast-like cells and fibronectin EDA (EDA-FN) as an indicator of renal fibrosis. After 1 year of treatment, proteinuria significantly decreased in the corticosteroid group. Histological findings, such as mesangial cell proliferation, mesangial matrix accumulation, and cellular crescents, showed significant improvement in the corticosteroid group but not in the antiplatelet group. Expression of alphaSMA in glomeruli significantly decreased in the corticosteroid group but not in the antiplatelet group. EDA-FN did not change in either group. We conclude that early treatment with corticosteroids for adult diffuse proliferative IgA nephropathy is effective in reducing renal injury.

Increased expression of TGF-beta1 but not of its receptors contributes to human obstructive nephropathy

Increased expression of TGF-beta1 but not of its receptors contributes to human obstructive nephropathy.

BACKGROUND

Previous studies have revealed an increased expression of transforming growth factor-beta1 (TGF-beta1) and deposition of extracellular matrix in the kidney of animals with ureteral obstruction. However, these relationships have not been elucidated in the hydronephrotic kidney of humans.

METHODS

We analyzed the tissue expression of extracellular matrix proteins, TGF-beta1, and its receptors in the human kidney with ureteral obstruction by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR). Obstructed kidneys (OBKs) were obtained from patients with ureteral tumors. A kidney specimen from patients with a renal tumor was used as control (CNKs).

RESULTS

The interstitial volume was significantly increased in OBKs in comparison with CNKs. OBKs showed increased deposition of collagen types I and IV and fibronectin in the renal interstitium. RT-PCR revealed overexpression of collagen alpha1(IV) mRNA and fibronectin mRNA in OBKs. OBKs showed a significantly increased mRNA expression of TGF-beta1 in comparison with CNKs. The immunoreactivity for TGF-beta1 increased markedly in the interstitium of OBKs. There was a significant correlation between the TGF-beta1 mRNA level and the interstitial volume. However, there was no significant difference between OBKs and CNKs in the relative mRNA level nor in immunoreactivity for TGF-beta receptors.

CONCLUSIONS

These data suggest that TGF-beta1 may contribute to the interstitial fibrosis found in the human kidney with ureteral obstruction, mainly because of an increase in the expression of this cytokine without significant changes to its receptors.

Suppression of transforming growth factor-beta isoforms, TGF-beta receptor type II, and myofibroblast differentiation in cultured human corneal and limbal fibroblasts by amniotic membrane matrix

Down-regulation of the transforming growth factor-beta (TGF-beta) signaling system is a strategy for preventing scarring during wound healing. Human corneal and limbal fibroblasts were cultured on the stromal matrix side of preserved human amniotic membrane. The levels of TGF-beta1, beta2, and beta3 and TGF-beta type II receptor transcripts and TGF-beta1 and beta2 proteins were suppressed as early as 8 hr and more dramatically at 24 hr after contact with an amniotic membrane. This suppressive effect was accompanied by down-regulation of alpha-smooth muscle actin, EDA spliced form of fibronectin, and integrin alpha5. It persisted even when challenged by 10 ng/ml TGF-beta1. In contrast with their counterparts grown on plastic or in collagen gel, such suppression in amniotic membrane cultures remained complete after 1 week of culturing. Cells cultured on amniotic membrane showed significantly reduced [3H]-thymidine incorporation compared to cells cultured on plastic and displayed no DNA fragmentation. These results reveal a novel mechanism by which the TGF-beta signaling system, DNA synthesis, and subsequent myofibroblast differentiation can be suppressed by an amnionic membrane matrix. This action explains in part the antiscarring results of amniotic membrane transplantation used for ocular surface reconstruction, a surgical technique applicable to other subspecialties. It may also explain in part why fetal wound healing is scarless.

Up-regulation of intracellular calcium, cyclic adenosine monophosphate and fibronectin synthesis in tubuar epithelial cells by complement

The terminal complement complex C5b-9 is known to participate in inflammatory processes including glomerular or tubulointerstitial injury. Injury appears to be a direct consequence of C5b-9-mediated cell stimulation. In that context we studied activation of tubular epithelial cells by C5b-9 particularly with regard to fibronectin synthesis and the transmembrane signals involved. C5b-9 in sublytic concentrations caused a rise of intracellular calcium and of cAMP, followed by an increase in abundance of fibronectin-specific mRNA and accumulation of protein. Stabilized cAMP or increasing the cAMP level by forskolin enhanced fibronectin synthesis with similar kinetics. The effect of cAMP could be enhanced by adding a calcium ionophore. Since the fibronectin gene is known to have a cAMP-responsive element, the data suggest that C5b-9 increases fibronectin synthesis via generation of cAMP.

Extracellular matrix-related genes in kidney after ischemic injury: potential role for TGF-beta in repair

The renal expression of transforming growth factor-beta1 (TGF-beta1) is enhanced following induction of ischemic injury in rat. In cultured renal cells, TGF-beta stimulates the synthesis of extracellular matrix. To link TGF-beta1 expression with the regulation of extracellular matrix postischemia, we characterized the expression of several genes known to regulate extracellular matrix synthesis at various times during recovery from acute ischemic renal injury in rat. Levels of mRNA for plasminogen activator inhibitor-1 (PAI-1), tissue inhibitor of metalloprotease-1 (TIMP-1), alpha1(IV) collagen, and fibronectin-EIIIA (FN-EIIIA) mRNAs were significantly enhanced in kidneys within 12 h to 3 days after injury and remained elevated at 7-28 days postischemia relative to levels in kidneys of sham-operated controls. PAI-1 mRNA and peptide were localized in regenerating proximal tubules at 3 and 7 days postischemic injury. alpha1(IV) Collagen and FN-EIIIA mRNAs were expressed primarily in regenerating proximal tubule cells. Immunoreactivity for FN-EIIIA was enhanced in the tubular basement membrane (TBM) of regenerating proximal tubules, and alpha1(IV) collagen immunoreactivity was detected in thickened tubulointerstitial spaces. In contrast, TIMP-1 immunoreactivity was enhanced in distal nephron structures postischemia. Immunoneutralization of TGF-beta in vivo attenuated the increases in FN-EIIIA, alpha1(IV) collagen, PAI-1, and TIMP-1 mRNAs by 52%, 73%, 43%, and 27%, respectively. These data are consistent with TGF-beta expression postischemic injury participating in renal regeneration of extracellular matrix homeostasis in the proximal TBM.

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.

Preparation of phage antibodies to the ED-A domain of human fibronectin

The fibronectin (FN) isoform containing the alternative spliced ED-A domain is much more expressed in fetal, tumoral, and regenerating tissues than in normal adult tissues. The ED-A containing FN is up-regulated by numerous cytokines, such as TGF-beta, and, although in normal adult liver the ED-A domain is undetectable, in regenerating rat liver the expression of ED-A is increased and mediates the conversion of fat storing cells to myofibroblasts. Here we describe the selection from a phage display library and the characterization of human antibody fragments directed against the ED-A sequence of FN. As they can be easily radiolabeled with 32P, these antibodies are very highly sensitive reagents for the determination of ED-A levels in tissues and biological fluids; in fact, use of these scFv induced a more than 10-fold increase in sensitivity with respect to the murine monoclonal IST-9. The possibility of preparing a range of human engineered antibodies should facilitate the development of antibody reagents with suitable pharmacokinetics, valency, functional affinity, and effector functions and that could be useful for clinical purposes.

Role of integrins in enterocyte migration

1. Enterocyte motility depends critically on cell-matrix interactions. Although still incompletely understood, these appear critically dependent upon integrin-mediated cell adhesion. 2. In addition to providing a mechanism for cell adhesion and traction, the integrins are likely to serve as true receptors for the matrix across which cell motility occurs, initiating signals by both mechanical and chemical means that alter cell phenotype and proliferation as well as cell motility. 3. Sound rationale now exists to postulate that soluble growth factors within the extracellular milieu regulate intestinal mucosal healing not only directly but also indirectly by modulating integrin expression and organization.

Matrix and adhesion molecules in kidney pathology: recent observations

The purpose of this article is to review a set of recently obtained data concerning matrix and matrix adhesion molecules in renal disease. Our goal is not to cover the entire topic, but rather to focus on findings obtained with an experimental model for chronic lupus nephritis, evoked in mice by inducing graft-versus-host disease (GVHD). The overall aim of these studies was to investigate the role of adhesion molecules as targets for autoantibodies, in the recruitment of inflammatory cells, and in the accumulation of matrix in kidney disorders. In addition, we set out to discover how matrix proteins in renal diseases differ from normal matrix molecules both quantitatively, in their increased frequency, and qualitatively, in their intramolecular structure. The advances in understanding and methodology described in this review imply a substantial capability for greater insight into the pathogenesis of kidney disease; for making better use of renal biopsies, such as in applying competitive reverse-transcriptase-polymerase chain reaction (RT-PCR) in RNA analysis for matrix; and in developing more effective treatment strategies for patients with kidney disease.

Role of transforming growth factor-beta 1 in glomerulonephritis

The role of transforming growth factor-beta 1 (TGF-beta 1) in human glomerulonephritis is still poorly understood. The relationship between expression of TGF-beta 1 protein or TGF-beta 1 mRNA and tissue damage was investigated using the enzyme-antibody and in situ hybridization method in frozen slices of renal tissue from 30 patients: 25 with glomerulonephritis (18 with immunoglobulin A nephropathy; two with focal glomerulosclerosis, one with membranous nephropathy, one with crescentic glomerulonephritis and three with lupus nephritis) and five control patients with minimal change disease. The expression of TGF-beta 1 mRNA was high in sclerotic and proliferative glomeruli, as well as in the tubular epithelial cells within tubulointerstitial lesions. There was significant correlation between the severity of tissue damage in immunoglobulin A nephropathy and the presence of TGF-beta 1 protein and TGF-beta 1 mRNA. These findings suggest that TGF-beta 1 is involved in glomerulosclerosis and the development of tubulointerstitial lesions, indicating its potential importance in the progression and aggravation of immunoglobulin A nephropathy.

Fibronectin production by human tubular cells: the effect of apical protein

In progressive renal disease the degree of renal failure correlates with interstitial scarring and the rate of progression correlates with the degree of proteinuria. This has led to the hypothesis that proteinuria may cause interstitial scarring. Human tubular cells (HTC) grown on permeable membrane supports were characterized to be predominantly of proximal tubular origin. HTC produce the matrix protein fibronectin in a polarised fashion the ratio of basolateral to apical secretion being 2.9 +/- 0.2 at 48 hours. The addition of serum proteins (1.0 mg/ml) to the apical medium resulted in increased basolateral secretion of fibronectin, 2.62 +/- 0.23-fold after 24 hours and 2.40 +/- 0.16-fold after 48 hours. Serum fractionation revealed that the stimulant to fibronectin production had a molecular weight 40 to 100 kDa. Platelet derived growth factor secretion was also stimulated to apical exposure to serum but transforming growth factor beta secretion was not detected. Addition of neutralizing anti-PDGF antibodies did not decrease fibronectin secretion. The activity of serum was not reproduced by albumin or by transferrin. Exposure of HTC to serum resulted in increased release of lactate dehydrogenase, suggesting a degree of cytotoxicity. This evidence could provide a mechanism for the link between proteinuria and interstitial scarring.