Influence of collagen gel substrata on certain biochemical activities of hepatocytes in primary culture

Effect of a hepatocyte growth factor/heparin-immobilized collagen system on albumin synthesis and spheroid formation by hepatocytes

A hepatocyte growth factor (HGF)/heparin-immobilized collagen system was used as a synthetic extracellular matrix for hepatocyte culture. The albumin synthesis, nucleus numbers and morphology of the hepatocytes were determined separately to evaluate the hepatocyte number and hepatocyte-specific function under this system. The benefits of the HGF/heparin-immobilized collagen system for hepatocyte culture were confirmed by three types of culture methods in vitro, namely 2D film cultures, 2D gel cultures and 3D gel cultures. In 2D collagen film cultures, hepatocytes exhibited the highest albumin synthesis (1.42 microg/well/day) in HGF/heparin-immobilized collagen films at 7 days of culture. Heparin inhibited hepatocyte adhesion while HGF promoted hepatocyte migration, and spheroid formation was easily detected in HGF/heparin-immobilized collagen films. In 2D collagen gel cultures, albumin synthesis of around 15 microg/well/day was detected and maintained for more than 18 days on HGF/heparin-immobilized collagen gels. Similar findings were obtained in 3D HGF/heparin-immobilized collagen gel cultures, which exhibited albumin synthesis of up to 30 microg/well/day. The albumin synthesis by hepatocytes was two-fold higher in 3D gel cultures compared with 2D gel cultures, and was maintained for over 2 weeks compared with 2D film cultures using the HGF/heparin-immobilized collagen system. Taken together, the HGF/heparin-immobilized collagen system was effective for albumin synthesis by hepatocytes in both 2D film cultures and 3D gel cultures, and therefore shows good potential for tissue engineering use.

Monocyte macrophage differentiation in vitro: Fibronectin-dependent upregulation of certain macrophage-specific activities

Transendothelial migration of monocytes followed by their differentiation into macrophages involves interaction of monocytes with subendothelial matrix. The influence of extracellular matrix on monocyte-macrophage differentiation was studied using an in vitro model system with human PBMC maintained on different matrix protein substrata. Upregulation of macrophage specific marker activities such as endocytosis of modified proteins, changes in expression of cell surface antigen, and production of matrix metalloproteinases was studied. Cells maintained on Fibronectin (Fn) showed significantly higher rate of endocytosis and production of MMP2 and MMP9 when compared to other matrix protein substrata. Immunoblot analysis, ELISA, and zymography showed that Fn-dependent upregulation of MMPs was blocked by antibodies to alpha(5)beta(1) integrin indicating that the Fn effect was mediated by integrins. The Fn effect on mo-mPhi was blocked by genistein and herbimycin. As monocytes differentiate to macrophages there was an increase in the rate of production of Fn. These results indicate the influence of the microenvironment of the cell, particularly Fn, on mo-mPhi differentiation and integrin-mediated downstream signaling through focal adhesion kinase and Src type tyrosine kinase is involved in this.

Monocyte-macrophage differentiation in three dimensional collagen lattice

Human peripheral blood mononuclear cells (PBMC) upon transendothelial migration interact with subendothelial matrix components and differentiate into macrophages. In order to study whether the shape of the cells as dictated by the extracellular matrix can influence monocyte-macrophage (mo-m(phi)) differentiation, human PBMC were maintained in vitro on a three dimensional collagen I (COL I) lattice and studied for various macrophage specific functions, viz. endocytosis of [(125)I]acetyl bovine serum albumin (BSA), expression of specific cell surface antigens and expression of matrix metalloproteinases (MMPs). The cells maintained in three dimensional COL gel exhibited a higher rate of endocytosis of [(125)I]acetyl BSA than those on COL-coated plastic. FACS analysis showed that the mean fluorescence intensity (MFI) corresponding to monocyte specific LPS receptor CD14 was significantly decreased while MFI corresponding to macrophage specific transferrin receptor CD71 was significantly increased in cells maintained in vitro on three dimensional COL gel compared to two dimensional COL substrata. Expression of macrophage specific MMPs (gelatinase A and gelatinase B) was significantly high in cells maintained on COL gel than on COL I-coated plastic. Appearance of 67 kDa gelatinase in the COL gel suggested that induction as well as activation of MMPs occur when cells are maintained in a three dimensional environment. These results indicate that monocytes undergo a rapid rate of differentiation when maintained in vitro on three dimensional COL I lattice suggesting that apart from the chemical nature of the matrix, the shape of the cells as provided by the matrix also influences mo-m(phi) differentiation.

Evaluation of the effect of culture matrices on induction of CYP3A isoforms in cultured porcine hepatocytes

Several bioartificial liver devices have been developed as temporary therapy for patients suffering from fulminant hepatic failure. Some of these devices contain porcine hepatocytes entrapped in collagen matrices. In order to improve the function of these BAL devices, there exists a need to optimize metabolic function of cultured hepatocytes. The goal of these investigations was to evaluate the effect of altering culture conditions on rifampin-mediated induction of CYP3A isoforms in cultured porcine hepatocytes. Midazolam metabolism was compared in porcine hepatocytes cultured in a monolayer configuration on collagen gels, in a sandwich configuration between collagen gels and a Matrigel overlay, and in spheroidal cultures. The effect of culture conditions was evaluated, by measuring CYP3A-mediated metabolism of midazolam and by immunoblotting to detect CYP3A proteins, in control cultures and in rifampin-treated cultures. Results obtained by normalizing the metabolism rate data to cell numbers (based on DNA content) present at the end of the culture experiment, showed that there was no difference between the different culture conditions tested. Our results suggest that culturing porcine hepatocytes as spheroids or in a sandwich configuration between collagen and Matrigel, offers no advantage in terms of CYP3A-mediated metabolic function on a per cell basis compared to culturing on collagen gels.

Effect of extracellular matrix on the expression of peroxisome proliferation associated genes in cultured rat hepatocytes

The purpose of this study was to determine whether the extracellular matrix used in hepatocyte culture would alter gene expression induced by the peroxisome proliferator ciprofibrate (CIP). We compared the activities and mRNA levels of two enzymes associated with peroxisome proliferation-fatty acyl-CoA oxidase (FAO), the first enzyme in the peroxisomal beta-oxidation pathway, and lauric acid hydroxylase (LAH), which represents the activity of the cytochrome P450 4A subfamily-in rat hepatocytes cultured on different plates: plastic, collagen-coated, thin and thick Matrigel, and collagen gel plates. CIP increased FAO activity about fivefold in collagen gel plates and sixfold in thick Matrigel plates compared to a fourfold increase in other plates; LAH was increased about threefold in thin Matrigel plates and fourfold in thick Matrigel and collagen gel plates compared to only a twofold increase in plastic and collagen-coated plates. The mRNA level for FAO was highest in hepatocytes cultured on collagen gel and Matrigel plates compared to those cultured on plastic and collagen-coated plates. The P-450 4A1 mRNA expression, however, was highest in the collagen gel plates, with lower expression in the thick Matrigel, collagen-coated and plastic plates. DNA synthesis and the DNA binding activity of the transcription factor AP-1 were also examined in response to epidermal growth factor (EGF) and CIP. Without the addition of EGF, DNA synthesis was significantly higher on collagen-coated plates than on collagen gel plates. The DNA binding activity of AP-1 was also induced after 24 hr culture in collagen-coated plates, whereas it was not detected in collagen gel plates. After the addition of EGF, the DNA binding activity of AP-1 was increased in both collagen-coated plates and collagen gel plates. CIP did not increase the DNA binding activity of AP-1 in either plate. These results demonstrate that components of the extracellular matrix influence the induction of peroxisome proliferator-induced enzyme activities and mRNA levels by CIP, with the highest induction seen in collagen gel and thick Matrigel plates. Furthermore, the induction of cell proliferation and AP-1 DNA binding activity are influenced by the extracellular matrix.

Regulation of the hepatocyte cell cycle by type I collagen matrix: role of cyclin D1

Rat hepatocytes adherent to a rigid film of type I collagen will spread and enter S phase, while those attached to collagen gel or a dried collagen substrate remain round and quiescent. The current studies were initiated to determine the mechanism by which these different substrates differentially influence cell cycle progression. Cyclin D1 mRNA and protein expression and associated kinase activity was low on dried collagen relative to collagen film. In contrast, cyclin E and cdk2 protein levels were similar on the two substrates. Although cyclin E and cdk2 were present, cells on dried collagen lacked cdk2 kinase activity. p27 protein levels did not differ between dried collagen and film, but more p27 was associated with cdk2 in cells on dried collagen than those on collagen film. Cyclin D1 expression on collagen film was inhibited by cytochalasin D and exoenzyme C3, suggesting a role for the GTP-binding protein, Rho, in regulating cyclin D1 expression. Cyclin D1 over-expression induced hepatocytes into S phase in the absence of cell shape change on dried collagen or collagen gel. These results demonstrate a novel, substrate-dependent mechanism for cyclin D1 expression in hepatocytes, and also demonstrate that cyclin D1 over-expression allows shape-independent S phase entry.

Dedifferentiation of human hepatocytes by extracellular matrix proteins in vitro: quantitative and qualitative investigation of cytokeratin 7, 8, 18, 19 and vimentin filaments

BACKGROUND/AIMS

Liver cirrhosis and carcinogenesis are accompanied by an alteration in extracellular matrix material. Histological studies reveal upregulation of the intermediate filaments cytokeratins 8 and 18 and de novo synthesis of vimentin, and cytokeratin 7 or 19 in hepatocytes. The aim of this study was to investigate how these two processes are linked.

METHODS

Human hepatocytes were seeded: (i) on the matrix components collagen I, IV, laminin, or fibronectin; (ii) on stoichiometrically different complete matrices, derived from human placenta (matrix I) or the Englebreth-Holm-Swarm tumor (matrix II), and (iii) inside a three-dimensional collagen I sandwich. Filament expression and assembly were measured by cytofluor analysis or confocal laserscan microscopy.

RESULTS

The matrix components or complete matrices triggered enhancement of cytokeratins 8 and 18 and de novo synthesis of cytokeratins 7, 19 and vimentin in a characteristic way. Confocal images demonstrated a dense and uniform network of cytokeratin 18 in freshly isolated cells, which was "replaced" by a few, thick protein bundles within 20 days. Interestingly, newly synthesized cytokeratin 19 structurally resembled the cytokeratin 19 organization in biliary epithelial cells. Marked cytokeratin alterations could be partially prevented when hepatocytes were grown in a three-dimensional collagen sandwich.

CONCLUSIONS

Pathological alterations to the chemical composition, molecular structure, or spatial arrangement of the liver matrix lead to specific changes in the intermediate filament pattern in human hepatocytes. We assume that degradation of the matrix results in pathological alterations to the hepatocyte-receptor matrix-ligand ratio, followed by a switch from physiological to pathological cell-activation.

Induction of tyrosine aminotransferase of primary cultured rat hepatocytes depends on the organization of microtubules

We investigated the relationship between the expression of tyrosine aminotransferase (TAT) and cytoskeletal systems of cultured rat hepatocytes by using serum-free culture conditions and changing three factors: 1) the concentration of calcium, 2) the dish-coating material, and 3) the cell-plating density. In hepatocytes in low-calcium medium, induction of TAT by dexamethasone and glucagon was maintained, although cell-cell adhesion was lost. Hepatocytes on Matrigel formed a nonspreading, spherical shape that provided them with the full extent of TAT activity without cell-cell adhesion. Hepatocytes plated on collagen at low cell density spread and changed shape, and the induction of TAT activity was markedly reduced. By using confocal laser-scanning microscopy, we analyzed the three-dimensional organization of cytoplasmic microtubules of hepatocytes maintaining the ability of TAT induction. Hepatocytes plated on collagen at low cell density possessed the radial filamentous structure of cytoplasmic microtubules. When the spherical shape of hepatocytes was maintained by cultivating cells on Matrigel, a ring-like structure of cytoplasmic microtubules beneath the plasma membrane was dominant. Moreover, the induction of TAT activity of hepatocytes in a standard culture system was strongly inhibited by the addition of 1 microM colchicine. These studies suggest that the organization of cytoplasmic microtubules may participate in the shape-related regulation of cell function.