Effects of extracellular matrix on the expression of peroxisomes in primary rat hepatocyte cultures

BACKGROUND/AIMS: Peroxisomes in wild-type cells vary between tissues and developmental stages. In the liver of some peroxisomal deficiency disorder patients, rare parenchymal cells express normal peroxisomes (mosaics); the mechanism is unknown. Our aim was to find factors regulating peroxisome expression. METHODS: Liver-specific as well as peroxisome characteristics were studied in three types of primary rat hepatocyte cultures. RESULTS: Total glutathione S-transferase activity and albumin secretion both increased in the collagen I sandwich and immobilization gel cultures. In contrast, in monolayers cultured on plastic, total glutathione S-transferase activity decreased and albumin secretion was only 30-40% compared to the collagen cultures. Glycogen rosettes typical of liver parenchymal cells were always abundant. Laminin and collagen IV-producing stellate cells were numerous in the monolayer but almost absent in the sandwich cultures. In 6-day-monolayer cultures, the number of liver-specific peroxisomes had decreased while atypical small or elongated peroxisomes appeared. Immunolabeling density for catalase and three beta-oxidation enzymes was decreased compared to adult rat liver; catalase specific activity in homogenates had dropped to 15% and 4% in the sandwich and monolayer cultures, respectively. In 17-day-sandwich cultures, some peroxisomes showed a very weak catalase reaction; total activity was 5%. Supplementation of the collagen type I cultures with several extracellular matrix factors could not prevent peroxisome dedifferentiation. CONCLUSION: The presence of these extracellular matrix components is not sufficient for normal peroxisome expression. It is suggested that hepatocyte-specific and peroxisomal features are regulated differently. The sandwich preserves hepatocyte differentiation better than the monolayer.     

Regulation of rat granulosa cell differentiation by extracellular matrix produced by bovine corneal endothelial cells

The effect of bovine corneal extracellular matrix (ECM) on gonadotropin-primed rat granulosa cells in vitro was studied by examining the following parameters: 1) rate of cell attachment to culture dishes; 2) modulation of cell morphology; 3) specific binding of [125I]human(h)CG to LH/hCG receptors; 4) cAMP response to hCG stimulation; and 5) basal and hCG stimulated progesterone production. Attachment of cells to culture dishes occurred significantly earlier on ECM, as compared with uncoated dishes (6 h vs. 24 h). Cells grown on ECM were epitheloid and organized in multilayer aggregates, closely resembling their organization in the intact wall of the ovarian follicle. In contrast, cultures on uncoated dishes grew as a monolayer of markedly flattened cells. A 2-fold increase in number of LH/hCG receptors occurred on ECM within 48 h, probably due to de novo synthesis. Scatchard analysis revealed no change in hormone affinity to the receptor during the culture period [association constant (Ka) = 2.5 X 10(10)M-1 for hCG]. Cells grown on ECM had a parallel increase in cAMP responsiveness to hCG stimulation. Cells grown in serum-free medium on ECM-coated dishes preserved only 50% of LH/hCG receptors and cAMP responsiveness after 48 h. Cells cultured on ECM showed a marked elevation in progesterone production even in the absence of gonadotropin stimulation, whereas cells grown on uncoated dishes almost completely lost their ability to produce progesterone both in the presence and absence of hCG. These results indicate that ECM plays a substantial role in the maintenance and further propagation of granulosa cell differentiation in vitro.     

Rho-associated kinases are crucial for myofibroblast differentiation and production of extracellular matrix in scleroderma fibroblasts

OBJECTIVE: Rho-associated kinases (Rock) are the major cellular mediators of Rho GTPases and play an important role in the organization of the actin cytoskeleton. Inhibitors of Rock are currently being evaluated for the treatment of pulmonary arterial hypertension. This study was undertaken to analyze the role of Rock in the activation of fibroblasts in systemic sclerosis (SSc). METHODS: Rock signaling was inhibited using chemical inhibitors and small interfering RNA. The expression of extracellular matrix (ECM) proteins and alpha-smooth muscle actin was analyzed by real-time polymerase chain reaction, Western blotting, and SirCol assay. Metabolic activity was quantified by MTT assay. Cell viability was assessed by staining with annexin V and propidium iodide. The role of MAP kinases was investigated using selective inhibitors and Western blotting. RESULTS: Inhibition of Rock strongly reduced the synthesis of the major ECM proteins at the messenger RNA level as well as the protein level. Counterregulatory changes in the expression of tissue inhibitors of metalloproteinases and matrix metalloproteinases were not observed. Inhibition of Rock prevented myofibroblast differentiation. Transforming growth factor beta activated ERK in a Rock-dependent manner, and ERK mediated in part the stimulatory effects of Rock on myofibroblast differentiation. Toxic adverse effects of the inhibition of Rock were not observed. CONCLUSION: Our findings demonstrate that Rock potently stimulates the differentiation of resting fibroblasts into myofibroblasts and the production of ECM at biologically relevant concentrations without cell toxicity. These findings, along with the beneficial effects of Rock inhibition on vascular disease, indicate that inhibition of Rock might be an interesting novel therapeutic approach for the treatment of SSc.     

Adhesion to the extracellular matrix is positively regulated by retinoic acid in HepG2 cells.

Aims: In this work, we aimed to investigate the possible modulation of cell-matrix interactions by retinoic acid (RA), in view of the well-known role of the extracellular matrix (ECM) and integrins in hepatocyte differentiation and proliferation. For this purpose, we analysed the adhesion ability of HepG2 cells on different substrates in the presence and absence of RA evaluating both the expression and cellular localisation of major proteins involved in focal contacts, using Western blot and confocal microscopy. RESULTS: A positive and substrate-dependent effect of RA on cell-matrix adhesion was observed after long-term culture. The increased adhesiveness in the treated cells was accompanied by an enhanced expression of beta1 and alpha3 integrin subunits, together with a redistribution of beta1 receptors clustered at the basal surface. In contrast, the levels of focal adhesion kinase (FAK), paxillin and alpha-actinin were unchanged, as was the phosphorylation state of FAK. Nonetheless, a stronger association between beta1 integrin and intracytoplasmatic proteins of focal contacts was observed in coimmunoprecipitation experiments after RA treatment, suggesting improved connection with the actin cytoskeleton. These results are consistent with previously described antiproliferative and differentiative effects of RA on transformed hepatocytes, and confirm the hypothesis of a direct influence of RA on specific adhesion molecules.     

Alveolar epithelial cell mesenchymal transition develops in vivo during pulmonary fibrosis and is regulated by the extracellular matrix

Mechanisms leading to fibroblast accumulation during pulmonary fibrogenesis remain unclear. Although there is in vitro evidence of lung alveolar epithelial-to-mesenchymal transition (EMT), whether EMT occurs within the lung is currently unknown. Biopsies from fibrotic human lungs demonstrate epithelial cells with mesenchymal features, suggesting EMT. To more definitively test the capacity of alveolar epithelial cells for EMT, mice expressing beta-galactosidase (beta-gal) exclusively in lung epithelial cells were generated, and their fates were followed in an established model of pulmonary fibrosis, overexpression of active TGF-beta1. beta-gal-positive cells expressing mesenchymal markers accumulated within 3 weeks of in vivo TGF-beta1 expression. The increase in vimentin-positive cells within injured lungs was nearly all beta-gal-positive, indicating epithelial cells as the main source of mesenchymal expansion in this model. Ex vivo, primary alveolar epithelial cells cultured on provisional matrix components, fibronectin or fibrin, undergo robust EMT via integrin-dependent activation of endogenous latent TGF-beta1. In contrast, primary cells cultured on laminin/collagen mixtures do not activate the TGF-beta1 pathway and, if exposed to active TGF-beta1, undergo apoptosis rather than EMT. These data reveal alveolar epithelial cells as progenitors for fibroblasts in vivo and implicate the provisional extracellular matrix as a key regulator of epithelial transdifferentiation during fibrogenesis.     

Murine granulosa cell morphology and function are regulated by a synthetic Arg-Gly-Asp matrix

Extracellular matrix (ECM) proteins are established regulators of granulosa cell survival, morphology, and differentiation. In this study, the roles of ECM adhesion peptide density on murine granulosa cell adhesion, morphology, and steroid secretion were probed using synthetic matrices. The synthetic matrix was fabricated from the polysaccharide alginate, which does not inherently support cell adhesion but can be modified with controlled densities of adhesion peptides (10(-4) to 2 x 10(-1) ng/cm(2)). GRM02, a murine granulosa cell line, and primary murine granulosa cells were cultured on alginate matrices modified by coupling of synthetic peptide sequences containing the Arg-Gly-Asp motif common to ECM proteins. Cells cultured on these peptide-modified surfaces (0.02, 0.2 ng/cm(2)) attached and spread, with morphologies specific to the peptide identity and density. Additionally, progesterone and estradiol secretion was a function of peptide density, with up to threefold increases compared to controls. These results indicate that the density and identity of adhesion peptides regulate granulosa cell function. This system provides a mechanism to examine the granulosa cell-ECM interactions that occur during follicle maturation.     

Changes in cell spreading and cytoskeletal organization are induced by adhesion to a fibronectin-fibrin matrix

Plasma fibronectin (pFN) cross-linked to fibrin during the injury response provides a provisional matrix required for cells to begin tissue repair. Using a synthetic matrix of pFN and fibrin as a substrate for cell adhesion and spreading, we have determined that pFN covalently cross-linked to fibrin into a complex multimer is functionally distinct from pFN immobilized onto a plastic surface. NIH- 3T3 cells on a FN-fibrin matrix reach 50% of the maximal cell area of cells spread on FN-coated plastic. They neither attach nor spread on cross-linked fibrin alone. Cells on pFN-fibrin matrices form few prominent stress fibers and exhibit clear differences in membrane ruffling and filopodial extension when stained with rhodamine-labeled phalloidin. Interestingly, these differences are enhanced by upregulation of protein kinase C. These data suggest that cell-FN interactions can be modified by the molecular context of the protein within the extracellular matrix resulting in distinct cell morphology and cytoskeletal organization.     

Insulin increases gelatinase activity in rat glomerular mesangial cells via ERK- and PI-3 kinase-dependent signalling

Diabetic nephropathy is associated with increased accumulation of the extracellular matrix (ECM) in the kidney, which ultimately leads to kidney failure. This may occur due to excessive synthesis of ECM components or reduced degradation, a process primarily mediated by matrix metalloproteinases (MMPs). The direct effect of insulin on ECM synthesis and degradation in glomerular mesangial cells (GMCs) is unclear. Here, we show an increased gelatinase activity in conditioned media from insulin-treated rat GMCs, determined by gelatin zymography. Furthermore, we show using the specific inhibitors LY294002 and PD98059 that insulin induced increased gelatinase activity via an intracellular signalling mechanism involving phosphatidylinositol-3 kinase (PI-3K) and the extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinases (MAPKs) respectively. In addition, we demonstrate that PI-3 kinase and ERK1/2 MAPK are activated by insulin in GMCs. The appearance of protease activity at approximately 72 kDa suggested that MMP-2 activity may be induced by insulin, however, we did not detect an increase in MMP-2 expression by Western blotting. In summary, our results suggest that insulin can induce gelatinase activity in GMCs, and it is possible that loss of this input in insulin-resistant type 2 diabetic individuals may contribute to ECM accumulation and the development of nephropathy.     

Mineralo- and glucocorticoid receptor mrnas are differently regulated by corticosterone in the rat hippocampus and anterior pituitary

In most cell lines and animal tissues, glucocorticoid receptors undergo downregulation after exposure to corticosterone. However, corticosterone treatment has not shown a consistent effect on mineralocorticoid (MR) and glucocorticoid receptors (GR) in the hippocampus, and it has been rarely assessed in the anterior pituitary. In this study we investigated dose-dependent effects of corticosterone on MR and GR mRNAs in the hippocampus and anterior pituitary. Adrenalectomized rats substituted with corticosterone in drinking fluid were injected subcutaneously with vehicle or 1, 10, 50, 100, or 200 mg of corticosterone, and sacrificed 4 h later. In the hippocampus we found a progressive decrease in MR and GR mRNAs with increasing doses of corticosterone. This was significant with 50 and 100 mg corticosterone for MR mRNA and with 10-200 mg corticosterone for GR mRNA at plasma corticosterone levels above 30 microg/dl. The anterior pituitary did not show significant changes at any dose. A time-course with 2 mg of corticosterone (non-response dose range at 4 h) revealed a significant decrease in MR and GR mRNAs in the hippocampus 8 h after the subcutaneous injection. In the anterior pituitary both mRNAs showed an increase that was significant 24 h after injection for MR and from 8 to 24 h for GR. In the hippocampus, adrenalectomy (absence of corticosterone) induced a significant increase in MR and GR mRNAs on day 3, but not on days 1, 8 and 21 after adrenalectomy. In the anterior pituitary there were no significant changes at any time after adrenalectomy. In summary, we have found an in vivo corticosterone dose- and time-dependent downregulation of MR and GR mRNAs in the hippocampus, whereas anterior pituitary MRs and GRs seem relatively insensitive to the excess or the absence of corticosterone, suggesting the lack of an autoregulatory effect in this tissue. Significant mRNA changes appearing later in time could suggest a secondary response via a glucocorticoid-induced gene product. Corticosteroid receptor downregulation in the hippocampus could prevent overstimulation or tissue damage when plasma corticosterone is high, while increased corticosteroid receptors in the anterior pituitary could buffer the excessive brain drive on the pituitary during chronic stress or pathological conditions associated with increased plasma glucocorticoids, such as depression.     

Phosphate stimulates matrix Gla protein expression in chondrocytes through the extracellular signal regulated kinase signaling pathway

Whereas increasing evidence suggests that inorganic phosphate (Pi) may act as a signaling molecule in mineralization-competent cells, its mechanisms of action remain largely unknown. The aims of the present work were to determine whether Pi regulates expression of matrix Gla protein (MGP), a mineralization inhibitor, in growth plate chondrocytes and to identify the involved signaling pathways. Chondrogenic ATDC5 cells and primary growth plate chondrocytes were used. Messenger RNA and protein analyses were performed by quantitative PCR and Western blotting, respectively. The activation and role of MAPKs were, respectively, determined by Western blotting and the use of specific inhibitors. Immunohistological detection of ERK1/2 was performed in rib organ cultures from newborn mice. The results indicate that Pi markedly stimulates expression of MGP in ATDC5 cells and primary growth plate chondrocytes. Investigation of the involved intracellular signaling pathways reveals that Pi activates ERK1/2 in a cell-specific manner, because the stimulation was observed in ATDC5 and primary chondrocytes, MC3T3-E1 osteoblasts, and ST2 stromal cells, but not in L929 fibroblasts or C2C12 myogenic cells. Accordingly, immunohistological detection of ERK1/2 phosphorylation in rib growth plates revealed a marked signal in chondrocytes. Finally, a specific ERK1/2 inhibitor, UO126, blocks Pi-stimulated MGP expression in ATDC5 cells, indicating that ERK1/2 mediates, mainly, the effects of Pi. These data demonstrate, for the first time, that Pi regulates MGP expression in growth plate chondrocytes, thereby suggesting a key role for Pi and ERK1/2 in the regulation of bone formation.     

Induction of CXCL1 by extracellular matrix and autocrine enhancement by interleukin-1 in rat pancreatic beta-cells

As we showed previously, the extracellular matrix (ECM) derived from rat bladder carcinoma cells (804G-ECM) has positive effects on rat primary beta-cell function and survival in vitro. The aim of this study was to define beta-cell genes induced by this ECM with a specific focus on cytokines. Analysis of differential gene expression by oligonucleotide microarrays, RT-PCR, and in situ hybridization was performed to identify cytokine mRNA induced by this matrix. Four cytokines were overexpressed on 804G-ECM compared with poly-L-lysine: C-X-C motif ligand 1 (CXCL1), CXCL2, interferon-inducible protein-10, and IL-1beta. A time-course experiment indicated that maximal induction by 804G-ECM of CXCL1/2 and interferon-inducible protein-10 occurred at 4 h. Stimulation of CXCL1 release by beta-cells on 804G-ECM was confirmed at the protein level. Moreover, secreted CXCL1 was shown to be functionally active by attracting rat granulocytes. Preventing the interaction of beta1 integrins and laminin-5 (a major component of 804G-ECM) with specific antibodies resulted in a 40-50% inhibition of CXCL1 expression. Using the nuclear factor-kappaB pathway inhibitor Bay 11-7082 it is demonstrated that CXCL1 expression and secretion are dependent on nuclear factor-kappaB activation. IL-1 secreted by beta-cells plated on 804G-ECM was found to be a key soluble mediator because treatment of cells with the IL-1 receptor antagonist significantly reduced both CXCL1 gene expression and secretion. It is concluded that ECM induces expression of cytokines including CXCL1 with amplification by IL-1 acting via a positive autocrine feedback loop.     

Growth and differentiation of adult rat hepatocytes regulated by the interaction between parenchymal and non-parenchymal liver cells

We have devised a medium which supports the continuous growth of hepatocytes without losing their replicative potential and differentiation capacity for a longer period. The medium HCGM, contains four key substances in addition to foetal bovine serum. They are epidermal growth factor, nicotinamide, ascorbic acid 2-phosphate and dimethylsulphoxide. When a non-parenchymal cell fraction containing small hepatocytes and non-parenchymal cells was cultured in HCGM, small hepatocytes grew clonally and differentiated into cells expressing either mature hepatocyte marker proteins or biliary cell marker proteins. Thus, for the first time, we showed the presence of a small compartment of bipotent and highly replicative clonogenic hepatocytes in the rat adult liver. HCGM also supported the growth of stellate cells (Ito cells) which were in the original preparation, suggesting the important role of stellate cells for the successful cultivation of hepatocytes. Together, these results suggest that a microenvironment is produced as a result of cooperative interactions between hepatocytes and stellate cells: one which stimulates the growth and differentiation of clonogenic hepatocytes.     

Dissociative extraction and reconstitution of extracellular matrix components involved in local bone differentiation.

Subcutaneous implantation of demineralized diaphyseal bone matrix in allogeneic rats results in the local induction of endochondral bone differentiation. We have explored the potential of three dissociative extractants, 4 M guanidine hydrochloride (Gdn . HCl), 8 M urea/1 M NaCl, and 1% NaDodSO4 at pH 7.4, containing protease inhibitors to solubilize putative inductive molecules in the bone matrix. Extraction of bone matrix with any one of these extracts resulted in the loss of the bone inductive property. The solubilized extracts were then reconstituted with the residue by dialysis against water. The various reconstituted matrices were bioassayed for bone inductive potential by quantitation of alkaline phosphatase activity and 45Ca incorporation on day 12 after implantation. There was complete recovery of biological activity after reconstitution of the residues with each of the three extracts. Polyacrylamide gel electrophoresis of the extracts revealed similar protein profiles. Gel filtration of the 4 M Gdn. HCl extract on Sepharose CL-4B showed a heterogeneous broad peak. When fractions of that peak containing proteins less than 50,000 daltons were reconstituted with inactive 4 M Gdn . HCl-treated bone matrix and then implanted, new bone was induced. These observations demonstrate the dissociative extraction and successful biological reconstitution of bone inductive macromolecules in demineralized bone matrix.