Bronchial epithelial cell matrix production in response to silica and basic fibroblast growth factor

BACKGROUND: Previous studies show that macrophages, lung fibroblasts, and their soluble mediators are responsible for the onset and development of pulmonary fibrosis. This study was conducted to determine whether airway epithelial cells are also directly involved in response to fibrogenic agents and consequently in the pathogenesis of lung fibrosis. To verify the hypothesis, we determined whether silica acts directly on human bronchial epithelial cells by stimulating cytokine and growth factor release and by modifying matrix production. MATERIALS AND METHODS: An SV40 large T antigen-transformed human airway epithelial cell line, 16HBE14o (16HBE), was used. The expression profile of some proinflammatory interleukins (ILs), such as IL-1alpha, IL-1beta and IL-6 and their modulation by silica, were evaluated by polymerase chain reaction (PCR) analysis. Transforming growth factor beta (TGFbeta) and basic fibroblast growth factor (bFGF) mRNA levels were tested by Northern blotting in the presence and in the absence of silica. The silica- and/or bFGF-induced effects on matrix components (total proteins, collagen, and fibronectin) were also evaluated using radio-labeled precursors. RESULTS: The results demonstrated 16HBE internalized silica particles. Silica induced a little IL-6 secretion, without affecting IL-1 and TGFbeta isoform production and strongly stimulated bFGF mRNA level and bFGF protein secretion. Silica also induced changes in 16HBE production of total proteins, collagen, and fibronectin production. When added in combination with the growth factor, it strengthened bFGF stimulation of matrix component secretion. CONCLUSIONS: These results support the hypothesis that the changes in matrix components are due to a direct effect of silica on bronchial epithelial cells. Silica-induced over-secretion of bFGF suggests that autocrine and paracrine differentiation loops for bFGF may also be operative and that these mechanisms may be involved in the pathogenesis of pulmonary fibrosis. In the future, cytokine-directed therapeutic strategies might find a place in clinical practice.     

Enhanced expression of fibroblast growth factor 2 in bone marrow cells and its potential role in the differentiation of hepatic epithelial stem-like cells into the hepatocyte lineage

The transplantation of bone marrow cells (BMCs) has been applied in liver regenerative cell therapy. However, details of the interaction between the transplanted BMCs and hepatic stem cells have not been elucidated. The aim of the present study was to investigate the interaction of BMCs with hepatic stem-like cells (HSLCs) and to determine the BMC factor that steers HSLC differentiation into the hepatocyte lineage. Both BMCs and HSLCs were obtained from an adult Sprague-Dawley rat, and a co-culture system was established. Cell proliferation was analyzed by a proliferation assay, and the differentiation of HSLCs into the hepatocyte lineage was evaluated by the detection of cellular mRNA for liver-specific proteins. DNA microarray analysis was applied to BMCs co-cultured with HSLCs to determine the genes upregulated by their interaction. The proliferation of HSLCs co-cultured with BMCs was significantly higher than that of HSLCs cultured alone, and the expression of mRNAs for both albumin and tryptophan-2,3-dioxygenase was detectable in the co-cultured HSLCs. DNA microarray analysis showed the upregulated expression of fibroblast growth factor 2 (FGF2) mRNA in BMCs co-cultured with HSLCs, and the expression of mRNAs for both albumin and tyrosine aminotransferase became detectable in HSLCs cultured with FGF2. Thus, BMCs stimulate both the proliferation of HSLCs and their differentiation into the hepatocyte lineage. FGF2 is one of the factors that is produced by the interacting BMCs and that stimulates this differentiation.     

Basic fibroblast growth factor stimulates hepatocyte growth factor/scatter factor secretion by human mesenchymal cells

Basic fibroblast growth factor (bFGF) together with other pleiotropic factors plays an important role in many complex physiological processes such as embryonic development, angiogenesis, and wound repair. Among these factors, hepatocyte growth factor/scatter factor (HGF/SF) which is secreted by cells of mesodermal origin exerts its mito- and motogenic activities on cells of epithelial and endothelial origin. Knowledge of the regulatory mechanisms of HGF/SF may contribute to the understanding of its role in physio-pathological processes. We observed that the secretion of HGF/SF by MRC-5 cells and by other fibroblast-derived cell cultures in conditioned media was enhanced by exposure to bFGF. HGF/SF was measured by the scatter assay, a bioassay for cell motility, and was further characterized by Western blot analysis with anti-HGF/SF antibodies. Exposure of MRC-5 cultures to 10 ng/ml of bFGF resulted already 6 h posttreatment in a threefold higher amount of scatter factor secreted into the medium as compared to untreated cultures. HGF/SF secretion was sustained after bFGF treatment for the following 72 h when increased amounts of HGF/SF were detected both in conditioned media as well as associated to the extracellular matrix. The secretion of HGF/SF in cell supernatants increased dose dependently upon treatment with bFGF starting from basal levels of 6 U/ml and reaching 27 U/ml at 30 ng/ml bFGF, plateauing thereafter. Upregulation of HGF/SF by IL-1, already described by others, was confirmed in this study. Based on our findings an articulated interaction can be speculated for bFGF, HGF/SF, and IL-1, e.g., in tissue regeneration during inflammatory processes or in wound healing. © 1996 Wiley-Liss, Inc.     

Engineering hepatocyte functional fate through growth factor dynamics: the role of cell morphologic priming.

We have reported previously that cellular stimulation induced by variable mechanochemical properties of the extracellular microenvironment can significantly alter liver-specific function in cultured hepatocytes (Semler et al., Biotech Bioeng 69:359-369, 2000). Cell activation via time-invariant presentation of biochemical growth factors was found to either enhance or repress cellular differentiation of cultured hepatocytes depending on the mechanical properties of the underlying substrate. In this work, we investigated the effects of dynamic growth factor stimulation on the cell growth and differentiation behavior of hepatocytes cultured on either compliant or rigid substrates. Specifically, hepatotrophic growth factors (epidermal and hepatocyte) were either temporally added or withdrawn from hepatocyte cultures on Matrigel that was crosslinked to yield differential degrees of mechanical compliance. We determined that the functional responsiveness of hepatocytes to fluctuations in GF stimulation is substrate specific but only in conditions in which the initial mechanochemical environment induced significant cell morphogenesis. Our studies indicate that in conditions under which hepatocytes adopted a "rounded" phenotype, they exhibited increased levels of differentiated function upon soluble stimulation and markedly decreased function upon the depletion of GF stimulation. In contrast, hepatocytes that assumed a "spread" phenotype exhibited slightly increased function upon the depletion of GF stimulation. By examining the functional responsiveness of hepatocytes of differential morphology to varied fluctuations in GF activation, insights into the ability of cell shape to "prime" hepatocyte behavior in dynamic microenvironments were elucidated. We report on the possibility of uncoupling and, thus, selectively manipulating, the concerted contributions of GF-induced cellular activation and substrate- and GF-induced cell morphogenesis toward induction of cell function.     

Ceramide-induced apoptosis: role of catalase and hepatocyte growth factor

The aim of this study was to elucidate cellular mechanisms involved in ceramide-induced apoptosis and its attenuation by hepatocyte growth factor (HGF). Human retinal pigmented epithelial cells (RPE) incubated with C2 ceramide accumulated reactive oxygen species (ROS) in mitochondria and underwent apoptosis in a dose-dependent manner. Ceramide-treated cells showed increased caspase-3 activation and an increase in mitochondrial membrane permeability transition (MPT). Low doses of H2O2 (100 microM) alone induced negligible apoptosis; however, ceramide-induced apoptosis was significantly enhanced by co-incubation with H2O2 (100 microM). Furthermore, ceramide treatment significantly decreased catalase enzymatic activity and protein expression. HGF pretreatment (20 ng/ml) significantly inhibited ceramide-induced apoptosis and reduced the accumulation of ROS, the activation of caspase-3, and the increase in MPT and prevented the reduction in catalase activity and expression. Together, the data suggest that ceramide induces apoptosis in RPE cells by increasing ROS production, MPT, and caspase-3 activation. The ceramide effect is potentiated by H2O2 and associated with a reduction in catalase activity, suggesting that catalase plays a central role in regulating this apoptotic response. The ability of HGF to attenuate these effects demonstrates its effectiveness as an antioxidant growth factor.     

In vitro regulation of pig Sertoli cell growth and function: effects of fibroblast growth factor and somatomedin-C

The effects of insulin, somatomedin-C (Sm-C), epidermal growth factor (EGF), fibroblast growth factor (FGF), vitamin E, and retinoic acid on growth and function of immature cultured pig Sertoli cells were investigated. All these factors, except vitamin E, stimulated Sertoli cell DNA synthesis and proliferation. The mitogenic effects of insulin observed only at micromolar concentrations were similar to those induced by nanomolar concentrations of Sm-C or EGF, but significantly less than those induced by FGF. The effects of EGF and Sm-C were almost additive, whereas those of Sm-C and FGF were synergistic. After a 6-day treatment, FGF and retinoic acid induced a significant increase in the number of follicle-stimulating hormone (FSH) receptors per cell, and in FSH-induced cyclic adenosine 3',5'-monophosphate (cAMP) production. Sm-C, which alone had no effect on these two parameters, potentiated FGF action. Basal plasminogen activator activity was enhanced after the 6-day treatment with EGF plus insulin and, particularly, with FGF plus insulin. Similarly, the response of the latter group to FSH was significantly higher than in any other group of cells. FGF was also able to stimulate cell multiplication and enhanced the FSH receptor number of Sertoli cells isolated from 15- and 26-day-old rats. Thus, FGF is the most potent known mitogenic factor for cultured Sertoli cells, and it stimulates the phenotypic expression of these cells.     

The emerging role of hepatocyte growth factor in renal diseases

Hepatocyte growth factor (HGF), a kringle-containing polypeptide, acts on various epithelial cells to regulate cell growth, cell motility, and morphogenesis. HGF also accelerates tissue regeneration of injured organs and is regarded as a key molecule in organ regeneration. Besides the regeneration of the liver, HGF also plays a role in the renal regeneration. In addition, an adaptive alteration of HGF status in various renal diseases occurs. However, the precise role of HGF in various renal diseases remains elusive. The signaling pathways of HGF may be associated with renal diseases. In this review, we will try to provide an in-depth understanding of the underlying role of HGF and its possible interactions with other molecules in renal diseases.     

Heparan sulfate is required for interaction and activation of the epithelial cell fibroblast growth factor receptor-2IIIb with stromal-derived fibroblast growth factor-7

Summary Fibroblast growth factor-7 (FGF-7) and a specific splice variant of the FGF tyrosine kinase receptor family (FGFR2IIIb) constitute a paracrine signaling system from stroma to epithelium. Different effects of the manipulation of cellular heparan sulfates and heparin on activities of FGF-7 relative to FGF-1 in epithelial cells suggest that pericellular heparan sulfates may regulate the activity of FGF-7 by a different mechanism than other FGFs. In this report, we employ the heparan sulfate-binding protein, protamine sulfate, to reversibly block cellular heparan sulfates. Protamine sulfate, which does not bind significantly to FGF-7 or FGFR2IIIb, inhibited FGF-7 activities, but not those of epidermal growth factor. The inhibition was overcome by increasing the concentrations of FGF-7 or heparin. Heparin was essential for binding of FGF-7 to recombinant FGFR2IIIb expressed in insect cells or FGFR2IIIb purified away from cell products. These results suggest that, similar to other FGF polypeptides, heparan sulfate within the pericellular matrix is required for activity of FGF-7. Differences in response to heparin and alterations in the BULK heparan sulfate content of cells likely reflect FGF-specific differences in the cellular repertoire of multivalent heparan sulfate chains required for assembly and activation of the FGF signal transduction complex.     

Identification of a fibroblast-derived epithelial morphogen as hepatocyte growth factor.

We have previously shown that Madin-Darby canine kidney (MDCK) epithelial cells grown in collagen gels in the presence of fibroblasts or fibroblast-conditioned medium (CM) form branching tubules, instead of the spherical cysts that develop under control conditions. We now report that the fibroblast-derived molecule responsible for epithelial tubulogenesis is hepatocyte growth factor (HGF). First, addition of exogenous HGF to cultures of MDCK cells induces formation of epithelial tubules. Second, the tubulogenic activity of fibroblast CM is completely abrogated by antibodies to HGF. These results demonstrate that HGF, a polypeptide that was identified as a mitogen for cultured hepatocytes, has the properties of a paracrine mediator of epithelial morphogenesis, and suggest that it may play important roles in the formation of parenchymal organs during embryonic development.     

Satellite cell activation in stretched skeletal muscle and the role of nitric oxide and hepatocyte growth factor

In the present study, we examined the roles of hepatocyte growth factor (HGF) and nitric oxide (NO) in the activation of satellite cells in passively stretched rat skeletal muscle. A hindlimb suspension model was developed in which the vastus, adductor, and gracilis muscles were subjected to stretch for 1 h. Satellite cells were activated by stretch determined on the basis of 5-bromo-2'-deoxyuridine (BrdU) incorporation in vivo. Extracts from stretched muscles stimulated BrdU incorporation in freshly isolated control rat satellite cells in a concentration-dependent manner. Extracts from stretched muscles contained the active form of HGF, and the satellite cell-activating activity could be neutralized by incubation with anti-HGF antibody. The involvement of NO was investigated by administering nitro-L-arginine methyl ester (L-NAME) or the inactive enantiomer N^G-nitro-D-arginine methyl ester HCl (D-NAME) before stretch treatment. In vivo activation of satellite cells in stretched muscle was not inhibited by D-NAME but was inhibited by L-NAME. The activity of stretched muscle extract was abolished by L-NAME treatment but could be restored by the addition of HGF, indicating that the extract was not inhibitory. Finally, NO synthase activity in stretched and unstretched muscles was assayed in muscle extracts immediately after 2-h stretch treatment and was found to be elevated in stretched muscle but not in stretched muscle from L-NAME-treated rats. The results of these experiments demonstrate that stretching muscle liberates HGF in a NO-dependent manner, which can activate satellite cells. muscle regeneration     

Novel regulation of fibroblast growth factor 2 (FGF2)-mediated cell growth by polysialic acid

Polysialic acid (polySia) is a unique polysaccharide that modifies neural cell adhesion molecule (NCAM) spatiotemporally. Recently, we demonstrated that polySia functions as a reservoir for several neurotrophic factors and neurotransmitters. Here, we showed the direct interaction between polySia and fibroblast growth factor-2 (FGF2) by native-PAGE, gel filtration, and surface plasmon resonance. The minimum chain length of polySia required for the interaction with FGF2 was 17. Compared with heparan sulfate, a well known glycosaminoglycan capable of forming a complex with FGF2, polySia formed a larger complex with distinct properties in facilitating oligomerization of FGF2, as well as in binding to FGF receptors. In polySia-NCAM-expressing NIH-3T3 cells, which were established by transfecting cells with either of the plasmids for the expression of the polysialyltransferases ST8SiaII/STX and ST8SiaIV/PST that can polysialylate NCAM, FGF2-stimulated cell growth, but not cell survival, was inhibited. Taken together, these results suggest that polySia-NCAM might be involved in the regulation of FGF2-FGF receptor signaling through the direct binding of FGF2 in a manner distinct from heparan sulfate.     

Epidermal growth factor receptor-dependent regulation of integrin-mediated signaling and cell cycle entry in epithelial cells

Integrin-mediated adhesion of epithelial cells to extracellular matrix (ECM) proteins induces prolonged tyrosine phosphorylation and partial activation of epidermal growth factor receptor (EGFR) in an integrin-dependent and EGFR ligand-independent manner. Integrin-mediated activation of EGFR in epithelial cells is required for multiple signal transduction events previously shown to be induced by cell adhesion to matrix proteins, including tyrosine phosphorylation of Shc, Cbl, and phospholipase Cgamma, and activation of the Ras/Erk and phosphatidylinositol 3'-kinase/Akt signaling pathways. In contrast, activation of focal adhesion kinase, Src, and protein kinase C, adhesion to matrix proteins, cell spreading, migration, and actin cytoskeletal rearrangements are induced independently of EGFR kinase activity. The ability of integrins to induce the activation of EGFR and its subsequent regulation of Erk and Akt activation permitted adhesion-dependent induction of cyclin D1 and p21, Rb phosphorylation, and activation of cdk4 in epithelial cells in the absence of exogenous growth factors. Adhesion of epithelial cells to the ECM failed to efficiently induce degradation of p27, to induce cdk2 activity, or to induce Myc and cyclin A synthesis; subsequently, cells did not progress into S phase. Treatment of ECM-adherent cells with EGF, or overexpression of EGFR or Myc, resulted in restoration of late-G(1) cell cycle events and progression into S phase. These results indicate that partial activation of EGFR by integrin receptors plays an important role in mediating events triggered by epithelial cell attachment to ECM; EGFR is necessary for activation of multiple integrin-induced signaling enzymes and sufficient for early events in G(1) cell cycle progression. Furthermore, these findings suggest that EGFR or Myc overexpression may provoke ligand-independent proliferation in matrix-attached cells in vivo and could contribute to carcinoma development.