Culture matrix configuration and composition in the maintenance of hepatocyte polarity and function

Polymer substrate topography actively regulates the multicellular organization and liver-specific functions of cultured hepatocytes

This study examines the role of topography of porous synthetic polymer substrates in regulating the tissue-specific morphogenesis of cultured hepatocytes. Porous foams of amorphous 50/50 poly(D,L glycolic-co-lactic acid) (PGLA) with a wide range of controlled pore-size distributions ( approximately 1 to 100 microm) were used as culture model surfaces. We found that the induction of microporosity in PGLA substrates significantly improved cell attachment and viability in comparison to those observed on non-porous PGLA films. A detailed evaluation of cellular morphogenesis on the microporous matrices showed that hepatocellular organization was sensitively dependent on the topographical feature size of the foam surfaces. Foams with subcellular size voids ( approximately 3 microm) induced kinetics of two-dimensional hepatocyte reorganization, yet limited the extent of three-dimensional aggregation. In contrast, foams with supercellular size voids ( approximately 67-microm) restricted hepatocyte motility, thereby promoting the kinetics of 3D aggregation. At intermediate void sizes ( approximately 17 microm), both 2D and 3D reorganization kinetics were promoted. Albumin secretory kinetics progressively increased on all void size configurations, the most rapid and sustained kinetics observed in supercellular sized voids, which may serve to minimize cell-polymer contacts and maximize cell-cell contacts in 3D. Overall, these studies demonstrate that void topography of porous polymer substrates is a critical textural feature to induce short-term cell adhesion and viability, and to also selectively regulate the kinetics and extent of multicellular spreading versus 3D aggregation. By virtue of its effects on cell adhesion and morphogenesis, the void topography of nonphysiological polymer scaffolds also is a powerful variable to microengineer hepatospecific activity of tissue analogs.

Behavior of a cell line derived from normal human hepatocytes on non-physiological and physiological-type substrates: evidence for enhancement of secretion of liver-specific proteins by a three-dimensional growth pattern

The behavior of a recently described cell line, HH25, derived from normal human hepatocytes, has been investigated on several different substrates--tissue-culture plastic, glass, a thin layer of rat-tail collagen I, and thin layers or thick gels of extracellular matrix derived from the Engelbreth-Holm-Swarm murine sarcoma (EHS matrix). Cellular morphology, proliferation, and secretion of three hepatocyte-specific proteins (albumin, alpha1 acid glycoprotein, and alpha1 antitrypsin) have been examined. There were no differences in morphology, proliferation, or differentiated function in the cells on either plastic, glass, collagen, I, or a thin layer of EHS matrix, but on a thick EHS matrix gel the cells altered their morphology (forming three-dimensional colonies with canalicular-like structures) and their production of albumin and alpha1 acid glycoprotein was enhanced. This suggests that the enhanced differentiated function is associated with the morphological change (occurring only on the thick EHS gel) rather than with receptor-mediated cell-matrix interactions (which can also occur on the thin layer of EHS matrix). This cell line is therefore a good in vitro cellular model for the investigation of the roles of morphological changes and of cell-cell and cell-matrix interactions in the control of human hepatocyte behavior without the need for an extensive source of primary tissue.

Adhesion-guided in vitro morphogenesis in pure and mixed cell cultures

The ability to understand and control the morphogenesis of mammalian cells is a fundamental objective of cell and developmental biology and tissue engineering research. Numerous processes, both biochemical and biophysical in nature, have been studied in an attempt to elucidate the mechanisms underlying this behavior. We focus here on the contributions of biophysical phenomena to the morphogenetic behavior of pure and mixed cell populations on solid surfaces in vitro. These principles are illustrated using characteristic liver tissue cells as a model system. The studies discussed demonstrate that cell-substratum and cell-cell adhesive forces are critical determinants of the ultimate morphology, cytoarchitecture, and organization achieved by these cells in vitro.

Long-term culture of hepatocytes from human adults

A long-term primary human hepatocyte culture retraining liver-specific functions is important and essential for basic research and for the future development of hepatocyte-based applications. We established a normal hepatocyte culture system from excess normal tissues obtained from adult liver cancer patients who received partial liver resection. Hepatocytes were isolated after perfusion and enzymatic disaggregation, and were first maintained in hormonally defined media on a Matrigel matrix, and then transferred to collagen sandwich gel. The hepatocytes formed clusters on the Matrigel matrix and increased in size and numbers with time of culture and eventually grew into spheroids of variable sizes. After being transferred to collagen gel, the cells migrated outward from spheroids to form a monolayer with cuboidal or polygonal cell shapes with granular cytoplasm and continued to proliferate. Cellular functions specific for hepatocytes were analyzed using immunoblot assay for proteins specifically secreted by the liver cells on different days of culture. The cells secreted albumin, transferrin and alpha-fetoprotein consistently for more than 100 days, to a maximum of 150 days. Thus, we have established a long-term culture of hepatocytes from human adults, which will be useful for basic studies of liver physiology such as metabolism and morphogenesis, as well as for other applications in the study of infectious hepatitis, pharmacology, pharmacokinetics, and toxicology.

Differential expression and distribution of focal adhesion and cell adhesion molecules in rat hepatocyte differentiation

Hepatocytes in primary culture enter into clonal proliferation in the chemically defined hepatocyte growth medium in the presence of hepatocyte growth factor and epidermal growth factor. Hepatocyte proliferation is associated with loss of differentiated gene expression. Overlay of matrix derived from Engelbreth-Holm-Swarm mouse sarcoma (Matrigel) on proliferating hepatocytes induces reexpression of the hepatic differentiation marker genes. To explore the role of matrix in the differentiation process of hepatocytes, we examined the mRNAs of fibronectin, vitronectin, and entactin in proliferating hepatocytes and Matrigel-treated hepatocytes. Fibronectin mRNA increased in proliferating hepatocytes at days 2-10 and then decreased; however, vitronectin mRNA disappeared in proliferating hepatocytes and was reexpressed in Matrigel-treated hepatocytes. We also found that focal adhesion kinase and paxillin were strongly increased in Matrigel-treated hepatocytes, and E-cadherin and beta-catenin slightly increased in Matrigel-treated hepatocytes, suggesting that both cell-to-extracellular matrix and cell-to-cell interactions may be an essential part of hepatocyte differentiation. To evaluate the distribution of focal adhesion associated molecules and cell-to-cell adhesion molecules, Triton X-100 soluble and insoluble fractions were examined at days 8, 9, 10, and 11 in proliferating hepatocytes and Matrigel-treated cells. We found that E-cadherin in Triton X-100 insoluble fractions dramatically decreased in Matrigel-treated hepatocytes; however, beta-catenin strongly increased in Triton X-100 soluble fractions of Matrigel-treated hepatocytes. These results suggest that the distribution of both focal adhesion associated molecules and cell adhesion molecules are reorganized during the process of differentiation induced by overlay of Matrigel.

Benzo(a)pyrene-induced alterations in growth-related gene expression and signaling in precision-cut adult rat liver and kidney slices

Benzo(a)pyrene (BaP) and related aromatic hydrocarbons are suspected carcinogens; however, the molecular basis underlying tumorigenesis remains unclear. To identify acute molecular targets of BaP within the liver and kidney, precision-cut slices harvested from naive, adult female Sprague-Dawley rats were challenged with BaP (0.3-30 microM) for 0.5 to 24 h. BaP did not elicit cytotoxicity, as assessed by intracellular K+ and ATP content and histological evaluation over the 24-h period. To determine if molecular signaling pathways were maintained in precision-cut slices, induction of the aryl hydrocarbon receptor (AhR) pathway was assessed following BaP challenge. Induction of cytochrome P450IA1 (P450IA1) mRNA and protein expression was observed in both liver and kidney slices. c-fos and c-Ha-ras gene expression was enhanced in liver, but not kidney, slices by BaP. c-jun mRNA levels were decreased in liver and kidney slices, although the effect was earlier (0.5 h) in liver slices compared to kidney slices. BaP increased the DNA binding of nuclear proteins to the AP-1 consensus recognition element in liver, but decreased DNA binding in kidney slices. In contrast, DNA binding of NF-kappa B was not affected by BaP in either liver or kidney slices. These results suggest that acute BaP challenge is associated with altered expression of several growth-related genes and AP-1 signaling and establish precision-cut slices as a useful in vitro system to investigate the molecular basis of BaP-induced tumorigenesis, including organ-specific differences.

The importance of new processing techniques in tissue engineering

Tissue engineering offers the possibility to create completely natural tissue and replace failing or malfunctioning organs. In many cases, biocompatible, biodegradable polymers are utilized to either induce surrounding tissue and cell ingrowth or to serve as a temporary scaffold for transplanted cells to attach, grow, and maintain differentiated functions. Various processing techniques have therefore been developed to fabricate polymers with specific properties to meet the needs of a particular organ.

Polymer scaffolds must possess unique physical and chemical properties for specific applications and must satisfy some basic requirements for tissue engineering. These scaffolds may be implanted without cells, and the regeneration depends on ingrowth of surrounding tissue to such materials—a process known as tissue induction. Alternatively cells may be seeded into a porous polymer. The cell-polymer construct is then transplanted. In either case, one essential criterion for the scaffold is biocompatibility—that is, the polymer scaffolds and their degradation products should not invoke an adverse immune response or toxicity.

Because of the problems associated with long-term implants, such as infection, fibrous tissue formation, and the possible need for retrieval, the role of polymer scaffolds should only be a temporary one. The degradation rate is optimized to allow transplanted cells to proliferate and secrete their own extracellular matrix (ECM) while polymer scaffolds can vanish when necessary to leave enough space for new tissue growth. Biodegradability of a polymer is determined by its composition, molecular weight (MW), MW distribution, degree of crystallinity, and environmental conditions such as temperature and pH. Mechanical loading of the scaffold may affect its degradation.