Fibronectin regulates morphology, cell organization and gene expression of rat fetal hepatocytes in primary culture

Advances in the Study of Bioactive Nanoparticles for the Treatment of HCC and Its Postoperative Residual Cancer

Primary hepatocellular carcinoma (HCC, hepatocellular carcinoma) is the third leading cause of tumor death in the world and the second leading cause in China. The high recurrence rate at 5 years after surgery also seriously affects the long-term survival of HCC patients. For reasons such as poor liver function, large tumors, or vascular invasion, only relatively limited palliative treatment is available. Therefore, effective diagnostic and therapeutic strategies are needed to improve the complex microenvironment and block the mechanism of tumor development in order to treat the tumor and prevent recurrence. A variety of bioactive nanoparticles have been shown to have therapeutic effects on hepatocellular carcinoma and have the advantages of improving drug solubility, reducing drug side effects, preventing degradation in the blood, increasing drug exposure time, and reducing drug resistance. The development of bioactive nanoparticles is expected to complete the current clinical therapeutic approach. In this review, we discuss the therapeutic advances of different nanoparticles for hepatocellular carcinoma and discuss their potential for postoperative applications with respect to possible mechanisms of hepatocellular carcinoma recurrence. We further discuss the limitations regarding the application of NPs and the safety of NPs.

Induced Endothelial Cell-Integrated Liver Assembloids Promote Hepatic Maturation and Therapeutic Effect on Cholestatic Liver Fibrosis

The transplantation of pluripotent stem cell (PSC)-derived liver organoids has been studied to solve the current donor shortage. However, the differentiation of unintended cell populations, difficulty in generating multi-lineage organoids, and tumorigenicity of PSC-derived organoids are challenges. However, direct conversion technology has allowed for the generation lineage-restricted induced stem cells from somatic cells bypassing the pluripotent state, thereby eliminating tumorigenic risks. Here, liver assembloids (iHEAs) were generated by integrating induced endothelial cells (iECs) into the liver organoids (iHLOs) generated with induced hepatic stem cells (iHepSCs). Liver assembloids showed enhanced functional maturity compared to iHLOs in vitro and improved therapeutic effects on cholestatic liver fibrosis animals in vivo. Mechanistically, FN1 expressed from iECs led to the upregulation of Itgα5/β1 and Hnf4α in iHEAs and were correlated to the decreased expression of genes related to hepatic stellate cell activation such as Lox and Spp1 in the cholestatic liver fibrosis animals. In conclusion, our study demonstrates the possibility of generating transplantable iHEAs with directly converted cells, and our results evidence that integrating iECs allows iHEAs to have enhanced hepatic maturation compared to iHLOs.

Fibrinogen improves liver function via promoting cell aggregation and fibronectin assembly in hepatic spheroids

Many key functions performed by the liver depend on the interaction between parenchymal cells and the microenvironment comprised of neighboring cells and extracellular matrix. The biological macromolecules in the matrix, which are dynamically changing, participate in various physiological processes through interactions with cell surface receptors, antigens, and ion channels. We found the rat liver biomatrix scaffold (LBS) prepared from adult rats is more effective in enhancing the function of hepatic spheroids than those derived from newborn or senile rats. Combined with matrisome and bioinformatics analyses, we further found that the glycoproteins, fibronectin and fibrinogen may have special potential for improving hepatocyte function. Human primary hepatocyte organoids and HepaRG spheroids showed more mature hepatocyte phenotype after adding fibronectin and fibrinogen to the culture system. During the cultivation of hepatic spheroids, fibrinogen resulted in an increase in cell-cell junction by promoting cell aggregation and helping fibronectin to assemble on cell surface, which resulted in activation of Wnt/β-catenin pathway. Fibronectin-integrin αVβ1-Wnt/β-catenin may be the axis of signal transduction in parenchymal cell microenvironment. Importantly, fibrinogen enhances the signal transduction. These results suggest that the addition of fibronectin and fibrinogen to the 3D culture system is a new strategy for inducing parenchymal cell functional maturation.

Intact extracellular matrix component promotes maintenance of liver-specific functions and larger aggregates formation of primary rat hepatocytes

The extracellular matrix (ECM) in a liver-specific extracellular matrix (L-ECM) scaffold facilitates hepatocyte viability and maintains hepatocyte functions in vitro. However, whether an intact composition of ECM is required for an efficient ECM-based substrate design remains to be clarified. In this study, two L-ECM hydrogels, namely L-ECM I and L-ECM II, were prepared by pepsin solubilization at 4 °C and 25 °C, respectively. The solubility at 4 °C was 50% whereas that at 25 °C was 95%, thus indicating well-preserved L-ECM. Analysis confirmed higher ECM protein components (especially collagen) in L-ECM II, along with denser fiber network and larger fiber diameter. L-ECM II gel exhibited high compression strength and suitable viscoelastic properties. Furthermore, hepatocytes in L-ECM II showed higher expression of liver-specific functions in 3D culture and wider spread while maintaining the cell-cell contacts in 2D culture. Therefore, an intact L-ECM is important to realize effective substrates for liver tissue engineering.

Porcine hepatocytes culture on biofunctionalized 3D inverted colloidal crystal scaffolds as an in vitro model for predicting drug hepatotoxicity

As drug-induced hepatotoxicity represents one of the most common causes of drug failure, three-dimensional (3D) in vitro liver platforms represent a fantastic toolbox to predict drug toxicity and thus reduce in vivo animal studies and lessen drug attrition rates. The aim of this study is to establish a functional porcine hepatocyte culture using a biofunctionalized 3D inverted colloidal crystal (ICC) hydrogel platform. The performances of non-adhesive bare poly(ethylene glycol)diacrylate (PEGDA) ICCs and PEGDA ICCs coated with either collagen type I or fibronectin have been investigated. Porcine hepatocytes viability, morphology, hepatic-specific functions and patterns of gene expression have been evaluated over a period of two weeks in culture to test diclofenac, a well-known hepatotoxic drug. Interestingly, cells in the fibronectin-functionalized scaffold exhibit different aggregation patterns and maintain better liver-specific function than those in bare ICCs and in collagen functionalized scaffold. We concluded that the 3D cell culture environment and the presence of extracellular matrix (ECM) proteins, especially fibronectin, facilitate hepatocyte viability and maintenance of the liver-specific phenotype in vitro, and enable us to predict hepatotoxicity.

As drug-induced hepatotoxicity represents one of the most common causes of drug failure, three-dimensional in vitro liver platforms represent a fantastic toolbox to predict drug toxicity and reduce in vivo studies and drug attrition rates.

Optimal Hypoxia Regulates Human iPSC-Derived Liver Bud Differentiation through Intercellular TGFB Signaling

Timely controlled oxygen (O2) delivery is crucial for the developing liver. However, the influence of O2 on intercellular communication during hepatogenesis is unclear. Using a human induced pluripotent stem cell-derived liver bud (hiPSC-LB) model, we found hypoxia induced with an O2-permeable plate promoted hepatic differentiation accompanied by TGFB1 and TGFB3 suppression. Conversely, extensive hypoxia generated with an O2-non-permeable plate elevated TGFBs and cholangiocyte marker expression. Single-cell RNA sequencing revealed that TGFB1 and TGFB3 are primarily expressed in the human liver mesenchyme and endothelium similar to in the hiPSC-LBs. Stromal cell-specific RNA interferences indicated the importance of TGFB signaling for hepatocytic differentiation in hiPSC-LB. Consistently, during mouse liver development, the Hif1a-mediated developmental hypoxic response is positively correlated with TGFB1 expression. These data provide insights into the mechanism that hypoxia-stimulated signals in mesenchyme and endothelium, likely through TGFB1, promote hepatoblast differentiation prior to fetal circulation establishment.

Nanofibrous PLGA electrospun scaffolds modified with type I collagen influence hepatocyte function and support viability in vitro

A major challenge of maintaining primary hepatocytes in vitro is progressive loss of hepatocyte-specific functions, such as protein synthesis and cytochrome P450 (CYP450) catalytic activity. We developed a three-dimensional (3D) nanofibrous scaffold made from poly(l-lactide-co-glycolide) (PLGA) polymer using a newly optimized wet electrospinning technique that resulted in a highly porous structure that accommodated inclusion of primary human hepatocytes. Extracellular matrix (ECM) proteins (type I collagen or fibronectin) at varying concentrations were chemically linked to electrospun PLGA using amine coupling to develop an in vitro culture system containing the minimal essential ECM components of the liver micro-environment that preserve hepatocyte function in vitro. Cell-laden nanofiber scaffolds were tested in vitro to maintain hepatocyte function over a two-week period. Incorporation of type I collagen onto PLGA scaffolds (PLGA-Chigh: 100 µg/mL) led to 10-fold greater albumin secretion, 4-fold higher urea synthesis, and elevated transcription of hepatocyte-specific CYP450 genes (CYP3A4, 3.5-fold increase and CYP2C9, 3-fold increase) in primary human hepatocytes compared to the same cells grown within unmodified PLGA scaffolds over two weeks. These indices, measured using collagen-bonded scaffolds, were also higher than scaffolds coupled to fibronectin or an ECM control sandwich culture composed of type I collagen and Matrigel. Induction of CYP2C9 activity was also higher in these same type I collagen PLGA scaffolds compared to other ECM-modified or unmodified PLGA constructs and was equivalent to the ECM control at 7 days. Together, we demonstrate a minimalist ECM-based 3D synthetic scaffold that accommodates primary human hepatocyte inclusion into the matrix, maintains long-term in vitro survival and stimulates function, which can be attributed to coupling of type I collagen.

STATEMENT OF SIGNIFICANCE

Culturing primary hepatocytes within a three-dimensional (3D) structure that mimics the natural liver environment is a promising strategy for extending the function and viability of hepatocytes in vitro. In the present study we generate porous PLGA nanofibers, that are chemically modified with extracellular matrix proteins, to serve as 3D scaffolds for the in vitro culture of primary human hepatocytes. Our findings demonstrate that the use of ECM proteins, especially type I collagen, in a porous 3D environment helps to improve the synthetic function of primary hepatocytes over time. We believe the work presented within will provide insights to readers for drug toxicity and tissue engineering applications.

[Effect of porcine small intestinal submucosa extracellular matrix in promoting vitality and functional gene expression of hepatocyte]

Objective

To investigate the effect of porcine small intestinal submucosa extracellular matrix (PSISM) on the vitality and gene regulation of hepatocyte so as to lay the experimental foundation for the application of PSISM in liver tissue engineering.

Methods

The experiment was divided into two parts: ① BRL cells were cultured with 50, 100, and 200 μg/mL PSISM-medium which were prepared by adding PSISM into the H-DMEM-medium containing 10%FBS in groups A1, B1, and C1, and simple H-DMEM-medium served as a control (group D1); ② BRL cells were seeded on 1%, 2%, and 3% PSISM hydrogel which were prepared by dissolving PSISM in sterile PBS solution containing 0.1 mol/L NaOH in groups A2, B2, and C2, and collagen type I gel served as a control (group D2). At 1, 3, and 5 days after culture, the morphology and survival of liver cells were detected by the Live/Dead fluorescent staining. The cell vitality was tested by cell counting kit-8 (CCK-8) assay. And the relative expressions of albumin (ALB), cytokeratin 18 (CK18), and alpha-fetoprotein (AFP) in hepatocytes were determined by real-time fluorescent quantitative PCR (RT-qPCR).

Results

The Live/Dead fluorescent staining showed the cells survived well in all groups. CCK-8 results displayed that the absorbance ( A) value of group C1 was significantly higher than that of group D1 at 5 days after culture with PSISM-medium, and there was no significant difference between groups at other time points ( P>0.05). After cultured with PSISM hydrogels, the A values of groups A2, B2, and C2 were significantly higher than those of group D2 at 3 and 5 days ( P<0.05), the A value of group A2 was significantly higher than that of groups B2 and C2 at 5 days ( P<0.05), but there was no significant difference between groups at other time points ( P>0.05). RT-qPCR showed that the relative expressions of ALB and CK18 mRNA significantly increased and the relative expression of AFP mRNA significantly decreased in groups A1, B1, and C1 when compared with group D1 ( P<0.05). The relative expression of CK18 mRNA in group C1 was significantly lower than that in groups A1 and B1 ( P<0.05). The relative expressions of ALB and CK18 mRNA were significantly higher and the relative expression of AFP mRNA was significantly lower in groups A2, B2, and C2 than group D2 ( P<0.05); the relative expression of CK18 mRNA in group A2 was significantly higher than that in group B2 ( P<0.05), and the relative expression of AFP mRNA in group A2 was significantly lower than that in group C2 ( P<0.05), but no significant difference was found between other groups ( P>0.05).

Conclusion

PSISM has good compatibility with hepatocyte and can promote the vitality and functional gene expression of hepatocyte. PSISM is expected to be used as culture medium supplement or cell carrier for liver tissue engineering.

ECM proteins in a microporous scaffold influence hepatocyte morphology, function, and gene expression

It is well known that a three-dimensional (3D) culture environment and the presence of extracellular matrix (ECM) proteins facilitate hepatocyte viability and maintenance of the liver-specific phenotype in vitro. However, it is not clear whether specific ECM components such as collagen or fibronectin differentially regulate such processes, especially in 3D scaffolds. In this study, a series of ECM-functionalized inverted colloidal crystal (ICC) microporous scaffolds were fabricated and their influence on Huh-7.5 cell proliferation, morphology, hepatic-specific functions, and patterns of gene expression were compared. Both collagen and fibronectin promoted albumin production and liver-specific gene expression of Huh-7.5 cells, compared with the bare ICC scaffold. Interestingly, cells in the fibronectin-functionalized scaffold exhibited different aggregation patterns to those in the collagen-functionalized scaffold, a variation that could be related to the distinct mRNA expression levels of cell adhesion-related genes. Based on these results, we can conclude that different ECM proteins, such as fibronectin and collagen, indeed play distinct roles in the phenotypic regulation of cells cultured in a 3D environment.

Extracellular Matrix Functionalization and Huh-7.5 Cell Coculture Promote the Hepatic Differentiation of Human Adipose-Derived Mesenchymal Stem Cells in a 3D ICC Hydrogel Scaffold

In this study, we constructed a microporous hydrogel scaffold with hexagonally packed interconnected cavities and extracellular matrix (ECM)-functionalized interior surface, and systematically investigated the hepatic differentiation of human adipose-derived mesenchymal stem cells (hAD-MSCs) under the influence of three key factors: three-dimensional (3D) geometry, ECM presence, and coculture with hepatocyte-derived cell line. Results confirmed that (i) hepatic differentiation of hAD-MSC is more efficient in a 3D microporous scaffold than in 2D monolayer culture; (ii) the presence of both ECM components (fibronectin and collagen-I) in the scaffold is superior to collagen-I only, highlighting the importance of fibronectin; and (iii) coculture with Huh-7.5 hepatocyte-derived cells promoted liver-specific functions of the hAD-MSC-derived hepatocytes. The optimized differentiation process only took 21 days to complete, a time length that is shorter or at least comparable to previous reports, and more importantly, yielded an albumin production more than 10-fold higher than conventional 2D culture. Our approach of optimizing hAD-MSC hepatic differentiation could provide a potential solution to the challenges such as hepatocyte transplantation or the establishment of human physiologically relevant liver models in vitro.

Analysis of the biocompatibility of perfluoropolyether dimethacrylate network using an organotypic method

In this work, we have investigated the potential of perfluoropolyether (PFPE) polymers for use in biomaterial applications, especially in cell culture and tissue engineering. PFPE substrates were synthesized by the photocuring of liquid PFPE urethane dimethacrylate. These surfaces were then modified by ECM protein coatings and microstructuration, to promote cell adhesion and migration. The surface properties of PFPE and PDMS (used as a reference) samples were studied by static contact angle measurements and AFM imaging. Both polymer surfaces were hydrophobic, having sessile air-water contact angles superior to 100°. Collagen and fibronectin coatings were found to change the wettability of PFPE and PDMS samples. The biological testing of substrates was done using a liver organotypic culture to evaluate the migration and density of liver cells. The results over seven days of culture demonstrated that the migration and density of cells cultured under untreated PFPE were higher than the migration and density of cells cultured under PDMS. ECM protein coatings enhanced cell migration from liver explants cultured on PFPE or PDMS. Furthermore, these coatings were more efficient in the case of a PFPE sample. From a second series of tests, in which the PFPE was microstructured, it was found that microstructures promoted the formation of a 3D cell layer. These results indicate that PFPE polymers have a potential for use in the development of biomaterials for tissue engineering and cell culture.

Sequential morphological characteristics of murine fetal liver hematopoietic microenvironment in Swiss Webster mice

Embryonic hematopoiesis occurs via dynamic development with cells migrating into various organs. Fetal liver is the main hematopoietic organ responsible for hematopoietic cell expansion during embryologic development. We describe the morphological sequential characteristics of murine fetal liver niches that favor the settlement and migration of hematopoietic cells from 12 days post-coitum (dpc) to 0 day post-partum. Liver sections were stained with hematoxylin and eosin, Lennert’s Giemsa, Sirius Red pH 10.2, Gomori’s Reticulin, and Periodic Acid Schiff/Alcian Blue pH 1.0 and pH 2.5 and were analyzed by bright-field microscopy. Indirect imunohistochemistry for fibronectin, matrix metalloproteinase-1 (MMP-1), and MMP-9 and histochemistry for naphthol AS-D chloroacetate esterase (NCAE) were analyzed by confocal microscopy. The results showed that fibronectin was related to the promotion of hepatocyte and trabecular differentiation; reticular fibers did not appear to participate in fetal hematopoiesis but contributed to the physical support of the liver after 18 dpc. During the immature phase, hepatocytes acted as the fundamental stroma for the erythroid lineage. The appearance of myeloid cells in the liver was related to perivascular and subcapsular collagen, and NCAE preceded MMP-1 expression in neutrophils, an occurrence that appeared to contribute to their liver evasion. Thus, the murine fetal liver during ontogenesis shows two different phases: one immature and mainly endodermic (<14 dpc) and the other more developed (endodermic-mesenchymal; >15 dpc) with the maturation of hepatocytes, a better definition of trabecular pattern, and an increase in the connective tissue in the capsule, portal spaces, and liver parenchyma. The decrease of hepatic hematopoiesis (migration) coincides with hepatic maturation.

Three-dimensional perfusion bioreactor culture supports differentiation of human fetal liver cells

The ability of human fetal liver cells to survive, expand, and form functional tissue in vitro is of high interest for the development of bioartificial extracorporeal liver support systems, liver cell transplantation therapies, and pharmacologic models. Conventional static two-dimensional culture models seem to be inadequate tools. We focus on dynamic three-dimensional perfusion technologies and developed a scaled-down bioreactor, providing decentralized mass exchange with integral oxygenation. Human fetal liver cells were embedded in a hyaluronan hydrogel within the capillary system to mimic an in vivo matrix and perfusion environment. Metabolic performance was monitored daily, including glucose consumption, lactate dehydrogenase activity, and secretion of alpha-fetoprotein and albumin. At culture termination cells were analyzed for proliferation and liver-specific lineage-dependent cytochrome P450 (CYP3A4/3A7) gene expression. Occurrence of hepatic differentiation in bioreactor cultures was demonstrated by a strong increase in CYP3A4/3A7 gene expression ratio, lower alpha-fetoprotein, and higher albumin secretion than in conventional Petri dish controls. Cells in bioreactors formed three-dimensional structures. Viability of cells was higher in bioreactors than in control cultures. In conclusion, the culture model implementing three-dimensionality, constant perfusion, and integral oxygenation in combination with a hyaluronan hydrogel provides superior conditions for liver cell survival and differentiation compared to conventional culture.

Nanofabricated collagen-inspired synthetic elastomers for primary rat hepatocyte culture

Synthetic substrates that mimic the properties of extracellular matrix proteins hold significant promise for use in systems designed for tissue engineering applications. In this report, we designed a synthetic polymeric substrate that is intended to mimic chemical, mechanical, and topological characteristics of collagen. We found that elastomeric poly(ester amide) substrates modified with replica-molded nanotopographic features enhanced initial attachment, spreading, and adhesion of primary rat hepatocytes. Further, hepatocytes cultured on nanotopographic substrates also demonstrated reduced albumin secretion and urea synthesis, which is indicative of strongly adherent hepatocytes. These results suggest that these engineered substrates can function as synthetic collagen analogs for in vitro cell culture.

Hepatic non-parenchymal cells and extracellular matrix participate in oval cell-mediated liver regeneration

AIM: To elucidate the interaction between non-parenchymal cells, extracellular matrix and oval cells during the restituting process of liver injury induced by partial hepatectomy (PH).

METHODS: We examined the localization of oval cells, non-parenchymal cells, and the extracellular matrix components using immunohistochemical and double immunofluorescent analysis during the proliferation and differentiation of oval cells in N-2-acetylaminofluorene (2-AAF)/PH rat model.

RESULTS: By day 2 after PH, small oval cells began to proliferate around the portal area. Most of stellate cells and laminin were present along the hepatic sinusoids in the periportal area. Kupffer cells and fibronectin markedly increased in the whole hepatic lobule. From day 4 to 9, oval cells spread further into hepatic parenchyma, closely associated with stellate cells, fibronectin and laminin. Kupffer cells admixed with oval cells by day 6 and then decreased in the periportal zone. From day 12 to 15, most of hepatic stellate cells (HSCs), laminin and fibronectin located around the small hepatocyte nodus, and minority of them appeared in the nodus. Kupffer cells were mainly limited in the pericentral sinusoids. After day 18, the normal liver lobule structures began to recover.

CONCLUSION: Local hepatic microenvironment may participate in the oval cell-mediated liver regeneration through the cell-cell and cell-matrix interactions.

Transcription factor HNF and hepatocyte differentiation

To know the precise mechanisms underlying the life or death and the regeneration or differentiation of cells would be relevant and useful for the development of a regenerative therapy for organ failure. Liver-specific gene expression is controlled primarily at a transcriptional level. Studies on the transcriptional regulatory elements of genes expressed in hepatocytes have identified several liver-enriched transcriptional factors, including hepatocyte nuclear factor (HNF)-1, HNF-3, HNF-4, HNF-6 and CCAAT/enhancer binding protein families, which are key components of the differentiation process for the fully functional liver. The transcriptional regulation by these HNFs, which form a hierarchical and cooperative network, is both essential for hepatocyte differentiation during mammalian liver development and also crucial for metabolic regulation and liver function. Among these liver-enriched transcription factors, HNF-4 is likely to act the furthest upstream as a master gene in transcriptional cascade and interacts with other liver-enriched transcriptional factors to stimulate hepatocyte-specific gene transcription. A link between the extracellular matrix, changes in cytoskeletal filament assembly and hepatocyte differentiation via HNF-4 has been shown to be involved in the transcriptional regulation of liver-specific gene expression. This review provides an overview of the roles of liver-enriched transcription factors in liver function.

Proteins combination on PHBV microsphere scaffold to regulate Hep3B cells activity and functionality: A model of liver tissue engineering system

The synergistic effects of extracellular matrix (ECM) protein combinations on Hep3B cell proliferation and functions are studied herein. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) microspheres were covalently conjugated with three types of proteins, collagen (type I), laminin, and fibronectin, using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide cross linkers. Successful conjugations of protein molecules were verified by the presence of nitrogen peaks in X-ray photoelectron spectroscopy. The densities of grafted proteins were quantified using Micro-BCA kit. A human hepatoma cell line, Hep3B, was then cultured in vitro on the ECM proteins-modified microspheres for 2 weeks. Cell proliferation was estimated using MTT method, and two hepatic functions, albumin secretion and P-450 activity, were evaluated using ELISA and EROD assays, respectively. The results indicated that combination of the three ECM proteins on microsphere surfaces has a significant effect on the proliferation of Hep3B cells, thus better mimicking the in vivo environment for liver tissue engineering.

An Integrin-Specific Collagen-Mimetic Peptide Approach for Optimizing Hep3B Liver Cell Adhesion, Proliferation, and Cellular Functions

This study focused on mimicking collagen structurally and biologically using various peptide sequences toward realizing an artificial collagen-like biomaterial. Collagen-mimetic peptides (CMPs) incorporating integrin-specific glycine-phenylalanine-hydroxyproline-glycine-glutamate-arginine (GFOGER) sequence from residues 502 to 507 of collagen alpha(1)(I) were used as a bioadhesive matrix and grafted onto poly(3-hydroxybutyrate-co3-hydroxyvalerate) microspheres to optimize cell adhesion, proliferation, and functions. Cell recognition of these biomolecules appeared to be conformation dependent, with the CMP1 of higher triple helix stability being preferred. Absence of the GFOGER hexapeptide in the CMP1' and CMP2' caused an adverse effect on the level of cell adhesion (<10%). The GFOGER-containing triple-helical CMPs effectively inhibited cell adhesion to collagen in a competition assay. The cell-adhesion activity of the CMP1 was approximately 50% of that of collagen. The cell spreading on the CMP1 was comparable with that observed on collagen. The presence of the CMP1 promoted cell attachment and spreading on the microspheres and extensive cell proliferation and bridging. Slower cell proliferation was observed on the blank microspheres. Live-dead assay showed that most cells are viable after 10-day culture. The presence of CMP1 on the microspheres maintained the albumin secretion and P-450 activity levels of the liver cells for up to 14 days. Our results established the potential of CMP1 to create a collagen-like microenvironment for optimizing cellular responses for liver tissue engineering.

Differentiation of mesenchymal cells derived from human amniotic membranes into hepatocyte-like cells in vitro

Mesenchymal stem cells are believed to be involved in the formation of mesenchymal tissues, including bone, cartilage, muscle, tendon and adipose tissue. Interestingly, it has previously been reported that mesenchymal stem cells could also differentiate into endoderm-derived cells, such as hepatocytes. The amniotic membrane contains mesenchymal cells and is a readily available human tissue. Therefore, we investigated the potential of mesenchymal cells derived from human amniotic membrane (MC-HAM) to differentiate into hepatocytes. We analyzed the expression of hepatocyte-specific genes in MC-HAM before and after induction of differentiation into hepatocytes. We observed the expression of mRNAs encoding albumin, a-fetoprotein, cytokeratin 18 and alpha1-antitrypsin, but not those encoding glucose-6-phosphatase or ornithine transcarbamylase, prior to the induction of differentiation. However, immunocytochemistry revealed that albumin and alpha-fetoprotein were abundantly produced only after the induction of differentiation into hepatocytes. In addition, we observed the storage of glycogen, a characteristic feature of hepatocytes, using periodic acid-Schiff staining of MC-HAM induced to differentiate into hepatocytes. Overall, MC-HAM appear to be able to differentiate into cells possessing some characteristics of hepatocytes. Although further studies should be carried out to determine whether such in vitro-differentiated cells can function in vivo as hepatocytes. These cells may be useful in various applications that require human hepatocytes.

Trends in the development of microfluidic cell biochips for in vitro hepatotoxicity

Current developments in the technological fields of liver tissue engineering, bioengineering, biomechanics, microfabrication and microfluidics have lead to highly complex and pertinent new tools called "cell biochips" for in vitro toxicology. The purpose of "cell biochips" is to mimic organ tissues in vitro in order to partially reduce the amount of in vivo testing. These "cell biochips" consist of microchambers containing engineered tissue and living cell cultures interconnected by a microfluidic network, which allows the control of microfluidic flows for dynamic cultures, by continuous feeding of nutrients to cultured cells and waste removal. Cell biochips also allow the control of physiological contact times of diluted molecules with the tissues and cells, for rapid testing of sample preparations or specific addressing. Cell biochips can be situated between in vitro and in vivo testing. These types of systems can enhance functionality of cells by mimicking the tissue architecture complexities when compared to in vitro analysis but at the same time present a more rapid and simple process when compared to in vivo testing procedures. In this paper, we first introduce the concepts of microfluidic and biochip systems based on recent progress in microfabrication techniques used to mimic liver tissue in vitro. This includes progress and understanding in biomaterials science (cell culture substrate), biomechanics (dynamic cultures conditions) and biology (tissue engineering). The development of new "cell biochips" for chronic toxicology analysis of engineered tissues can be achieved through the combination of these research domains. Combining these advanced research domains, we then present "cell biochips" that allow liver chronic toxicity analysis in vitro on engineered tissues. An extension of the "cell biochip" idea has also allowed "organ interactions on chip", which can be considered as a first step towards the replacement of animal testing using a combined liver/lung organ model.

Galactosylated poly(vinylidene difluoride) hollow fiber bioreactor for hepatocyte culture

To overcome the limitations of long-term expression of highly differentiated hepatocyte functions, we have developed a novel bioreactor in which hepatocytes are seeded in a ligand-immobilized hollow fiber cartridge. Galactosylated Pluronic polymer is immobilized on poly(vinylidene difluoride) (PVDF) hollow fiber surface through an adsorption scheme yielding a substrate with hepatocyte-specific ligand and a hydrophilic surface layer, which can resist nonspecific protein adsorption and facilitate cell binding to the galactose ligand. Interestingly, the galactosylated PVDF hollow fiber shows enhanced serum albumin diffusion across the membrane. Freshly isolated rat hepatocytes were seeded and cultured in the extralumenal space of the hollow fiber cartridge for 18 days in a continuously circulated system. Albumin secretion function of the seeded hepatocytes was monitored by analyzing circulating medium by enzyme-linked immunosorbent assay. Urea synthesis and P-450 function (7-ethoxycoumarin dealkylase activity) were measured periodically by doping the circulating medium with NH4Cl and 7-ethoxycoumarin, respectively. Hepatocytes cultured on galactosylated PVDF hollow fibers maintained better albumin secretion and P-450 functions than on unmodified and serum-coated PVDF hollow fibers when cultured in serum-containing medium. Morphological examination by scanning electron microscopy showed that hepatocytes cultured on galactosylated PVDF hollow fibers developed significant aggregation, in contrast to those cultured on unmodified PVDF fibers or on serum-coated PVDF fibers. Transmission electron microscopy images revealed that tight junctions and canaliculus-like structures formed in these aggregates. These results suggest the potential application of this galactosylated PVDF hollow fiber cartridge for the design of a bioartificial liver assist device.

Galactose-carrying polymers as extracellular matrices for liver tissue engineering

Extracellular matrix (ECM) plays important roles in tissue engineering because cellular growth and differentiation, in the two-dimensional cell culture as well as in the three-dimensional space of the developing organism, require ECM with which the cells can interact. Especially, the bioartificial liver-assist device or regeneration of the liver-tissue substitutes for liver tissue engineering requires a suitable ECM for hepatocyte culture because hepatocytes are anchorage-dependent cells and are highly sensitive to the ECM milieu for the maintenance of their viability and differentiated functions. Galactose-carrying synthetic ECMs derived from synthetic polymers and natural polymers bind hepatocytes through a receptor-mediated mechanism, resulting in enhanced hepatocyte functions. Attachment and functions of hepatocytes were affected by physico-chemical properties including ECM geometry as well as the type, density and orientation of galactose. Also, cellular environment, medium composition and dynamic culture system influenced liver-specific functions of hepatocytes beside ECM.

Factors influencing stem cell differentiation into the hepatic lineage in vitro

A major area of research in transplantation medicine is the potential application of stem cells in liver regeneration. This would require well-defined and efficient protocols for directing the differentiation of stem cells into the hepatic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying hepatogenesis and liver metabolism. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for newly developed biomaterials and drugs, could also utilize protocols developed for the hepatic differentiation of stem cells. Hence, this review critically examines the various strategies that could be employed to direct the differentiation of stem cells into the hepatic lineage in vitro.

A fibronectin fragment induces tumor necrosis factor production of rat basophilic leukemia cells

Proteolytic digest of fibronectin (FN), but not intact FN, induced TNF-alpha secretion of rat basophilic leukemia (RBL-2H3) cells. As a result of the identification of FN fragment responsible for TNF-alpha secretion, a 30-kDa fragment derived from the carboxyl-terminal heparin-binding (Hep 2) domain of FN was isolated from the FN digest. The TNF-alpha secretion was abrogated by treatment of RBL-2H3 cells with cycloheximide, indicating the de novo synthesis of TNF-alpha, but not with polymyxin B, excluding the possible TNF-alpha induction by some contaminated lipopolysaccharides. A 22-mer synthetic peptide originated from the Hep 2 domain, termed FNIII14, which has been found to negatively modulate the beta1 integrin activation, had the ability to induce TNF-alpha production, whereas this activity of FNIII14 disappeared by shuffling a YTIYVIAL sequence essential for the integrin-inactivating activity. FNIII14 suppressed the spreading of RBL-2H3 cells on FN substrate, wherein RBL-2H3 cell proliferation was inhibited with FNIII14 in a dose-dependent manner. Thus, it appears that FN fragments containing the YTIYVIAL anti-adhesive site affect the activation status of RBL-2H3 mast cells, characterized by the stimulation of TNF-alpha production and growth suppression, probably due to negative regulation of beta1 integrin activity.

Immunolocalization of extracellular matrix components and integrins during mouse liver development

Intrahepatic biliary cell differentiation takes place in periportal hepatoblasts under the influence of the subjacent connective tissue, the mechanism of which is still unclear. This study was undertaken to analyze the immunolocalization of extracellular matrix components and their cellular receptors during mouse liver development, with special attention given to biliary differentiation and vascular development. In young fetal mouse liver, primitive structures of sinusoids were developed between hepatic cords associated with hematopoietic cells demonstrated by immunohistochemistry of basal laminar components, the alpha6 integrin subunit, and PECAM-1. Portal veins and hepatic veins showed different staining intensities of alpha2, alpha3, and alpha6 integrin subunits from early stages of development. Anti-beta4 integrin subunit antibodies reacted with portal veins, but not with hepatic veins after perinatal stages. Their different phenotypes may be related to the preferential differentiation of periportal bile ducts. In intrahepatic bile duct development, periportal hepatoblasts adjacent to the connective tissue were immunostained for each basal laminar component on the basal side at almost the same time; alpha3, alpha5, alpha6, and beta4 integrin subunits were immunohistochemically detectable later than the basal laminar components. These staining patterns of intrahepatic bile duct cells clearly differed from those of extrahepatic bile duct cells from the beginning of their development, suggesting that these ducts are of different origins. In conclusion, the vascular structures, including sinusoids, portal veins, and hepatic veins, develop from early stages of liver development, and the extracellular matrix components may play important roles in biliary differentiation and vascular development. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

High density of immobilized galactose ligand enhances hepatocyte attachment and function

Galactosylated surface is an attractive substrate for hepatocyte culture because of the specific interaction between the galactose ligand and the asialoglycoprotein receptor on hepatocytes. In this study, we described a scheme to achieve high density of immobilized galactose ligands on polyethylene terephthalate (PET) surface by first surface-grafting polyacrylic acid on plasma-pretreated PET film under UV irradiation, followed by conjugation of a galactose derivative (1-O-(6'-aminohexyl)-D-galactopyranoside) to the grafted polyacrylic acid chains. A high galactose density of 513 nmol/cm(2) on the PET surface was used in this study to investigate the behavior of cultured hepatocyte. This engineered substrate showed high affinity to fluorescein isothiocyanate-lectin binding. Primary rat hepatocytes, when seeded at a density of 2 x 10(5) cells/cm(2), attached to the galactosylated PET substrate at a similar efficiency compared with collagen-coated substrate. The hepatocytes spontaneously formed aggregates 1 day after cell seeding and showed better maintenance of albumin secretion and urea synthesis functions than those cultured on collagen-coated surface.

Polyvinylalcohol three-dimensional matrices for improved long-term dynamic culture of hepatocytes

Rat hepatocytes were seeded on three-dimensional highly porous polyvinylalcohol (PVA) and aminoethyl-modified polyvinylalcohol (AE-PVA) matrices. Hepatocytes were cultured under static and dynamic conditions. The three-dimensional matrices offered an improved extracellular microenvironment for long-term (5 days) maintenance of hepatocytes, compared to reference monolayer cultures on collagen. Cellular adhesion exceeded 80% with a viability superior to 70%. The preservation of albumin secretion after 5 days of culture was two times higher for static cultures on three-dimensional matrices (18% on PVA, 13% on AE-PVA) and three times higher for dynamic three-dimensional cultures (25% PVA and AE-PVA), compared to the static two-dimensional culture on collagen film (8%). The biotransformation of ammonia into urea was also maintained throughout the culture period. The addition of the aminoethyl function demonstrated no toxicity for the hepatocyte cultures. This function could be suitable eventually to further improve the hepatocyte culture system by linking more specific adhesion molecules on the polymer surface. This study demonstrated the efficiency of polyvinylalcohol as a three-dimensional matrix coupled to a perfusion culture system, which improves extracellular conditions for hepatocyte survival and promotes preservation of long-term hepatospecific functions.

Fetal liver stroma consists of cells in epithelial-to-mesenchymal transition

Liver becomes the predominant site of hematopoiesis by 11.5 dpc (days after coitus) in the mouse and 15 gestational weeks in humans and stays so until the end of gestation. The reason the liver is the major hematopoietic site during fetal life is not clear. In this work, we tried to define which of the fetal liver microenvironmental cell populations would be associated with the development of hematopoiesis and found that a population of cells with mixed endodermal and mesodermal features corresponded to hematopoietic-supportive fetal liver stroma. Stromal cells generated from primary cultures or stromal lines from mouse or human fetal liver in the hematopoietic florid phase expressed both mesenchymal markers (vimentin, osteopontin, collagen I, alpha smooth muscle actin, thrombospondin-1, EDa fibronectin, calponin, Stro-1 antigens, myocyte-enhancer factor 2C) and epithelial (alpha-fetoprotein, cytokeratins 8 and 18, albumin, E-cadherin, hepatocyte nuclear factor 3 alpha) markers. Such a cell population fits with the description of cells in epithelial-to-mesenchymal transition (EMT), often observed during development, including that of the liver. The hematopoietic supportive capacity of EMT cells was lost after hepatocytic maturation, induced by oncostatin M in the cell line AFT024. EMT cells were observed in the fetal liver microenvironment during the hematopoietic phase but not in nonhematopoietic liver by the end of gestation and in the adult. EMT cells represent a novel stromal cell type that may be generated from hepatic endodermal or mesenchymal stem cells or even from circulating hematopoietic stem cells (HSCs) seeding the liver rudiment.

Expression of a membrane-bound form of the ferroxidase ceruloplasmin by leptomeningeal cells

Ceruloplasmin is a key enzyme involved in detoxifying ferrous iron, which can generate free radicals. The secreted form of ceruloplasmin is produced by the liver and is abundant in serum. We have previously identified a membrane-bound glycosylphosphatidylinositol (GPI)-anchored form of ceruloplasmin (GPI-Cp) that is expressed by astrocytes in the central nervous system (CNS) (Patel and David. 1997. J Biol Chem 272:20185-20190). We now provide direct evidence that rat leptomeningeal cells, which cover the surface of the brain, also express GPI-Cp. The expression of GPI-Cp on the surface of these cells increases with postnatal development and is regulated in vitro by cell density, time in culture, and various extracellular matrix molecules. The expression of GPI-Cp also appears to be regulated differently in astrocytes and leptomeningeal cells in vitro. The abundant expression of GPI-Cp on the surface of leptomeningeal cells suggests that these cells play a role in antioxidant defense along the surface of the postnatal CNS possibly by detoxifying the cerebrospinal fluid.

Mechanisms controlling early development of the liver

Over the last decade significant advances have been made in our understanding of the molecular mechanisms that control early aspects of mammalian liver development. Studies using tissue explant cultures and molecular biology techniques as well as the analysis of transgenic and knockout mice have identified signaling molecules and transcription factors that are necessary for the onset of hepatogenesis. This review presents an overview of these studies and discusses the role of individual factors during hepatic development.

Multipotent adult progenitor cells from bone marrow differentiate into functional hepatocyte-like cells

We have derived from normal human, mouse, and rat postnatal bone marrow primitive, multipotent adult progenitor cells (MAPCs) that can differentiate into most mesodermal cells and neuroectodermal cells in vitro and into all embryonic lineages in vivo. Here, we show that MAPCs can also differentiate into hepatocyte-like cells in vitro. Human, mouse, and rat MAPCs, cultured on Matrigel with FGF-4 and HGF, differentiated into epithelioid cells that expressed hepatocyte nuclear factor-3beta (HNF-3beta), GATA4, cytokeratin 19 (CK19), transthyretin, and alpha-fetoprotein by day 7, and expressed CK18, HNF-4, and HNF-1alpha on days 14-28. Virtually all human, as well as a majority of rodent cells stained positive for albumin and CK18 on day 21; 5% (rodent) to 25% (human) cells were binucleated by day 21. These cells also acquired functional characteristics of hepatocytes: they secreted urea and albumin, had phenobarbital-inducible cytochrome p450, could take up LDL, and stored glycogen. MAPCs, which can be expanded in vitro and maintained in an undifferentiated state for more than 100 population doublings, can thus differentiate into cells with morphological, phenotypic, and functional characteristics of hepatocytes. MAPCs may therefore be an ideal cell for in vivo therapies for liver disorders or for use in bioartificial liver devices.

Multipotent adult progenitor cells from bone marrow differentiate into functional hepatocyte-like cells

We have derived from normal human, mouse, and rat postnatal bone marrow primitive, multipotent adult progenitor cells (MAPCs) that can differentiate into most mesodermal cells and neuroectodermal cells in vitro and into all embryonic lineages in vivo. Here, we show that MAPCs can also differentiate into hepatocyte-like cells in vitro. Human, mouse, and rat MAPCs, cultured on Matrigel with FGF-4 and HGF, differentiated into epithelioid cells that expressed hepatocyte nuclear factor-3beta (HNF-3beta), GATA4, cytokeratin 19 (CK19), transthyretin, and alpha-fetoprotein by day 7, and expressed CK18, HNF-4, and HNF-1alpha on days 14-28. Virtually all human, as well as a majority of rodent cells stained positive for albumin and CK18 on day 21; 5% (rodent) to 25% (human) cells were binucleated by day 21. These cells also acquired functional characteristics of hepatocytes: they secreted urea and albumin, had phenobarbital-inducible cytochrome p450, could take up LDL, and stored glycogen. MAPCs, which can be expanded in vitro and maintained in an undifferentiated state for more than 100 population doublings, can thus differentiate into cells with morphological, phenotypic, and functional characteristics of hepatocytes. MAPCs may therefore be an ideal cell for in vivo therapies for liver disorders or for use in bioartificial liver devices.