Development of Co-Culture System of Hepatocytes with Bone Marrow Cells for Expression and Maintenance of Hepatic Functions

Advances in multicellular spheroids formation

Three-dimensional multicellular spheroids (MCSs) have a complex architectural structure, dynamic cell-cell/cell-matrix interactions and bio-mimicking in vivo microenvironment. As a fundamental building block for tissue reconstruction, MCSs have emerged as a powerful tool to narrow down the gap between the in vitro and in vivo model. In this review paper, we discussed the structure and biology of MCSs and detailed fabricating methods. Among these methods, the approach in microfluidics with hydrogel support for MCS formation is promising because it allows essential cell-cell/cell-matrix interactions in a confined space.

Recent advances in three-dimensional multicellular spheroid culture for biomedical research

Many types of mammalian cells can aggregate and differentiate into 3-D multicellular spheroids when cultured in suspension or a nonadhesive environment. Compared to conventional monolayer cultures, multicellular spheroids resemble real tissues better in terms of structural and functional properties. Multicellular spheroids formed by transformed cells are widely used as avascular tumor models for metastasis and invasion research and for therapeutic screening. Many primary or progenitor cells on the other hand, show significantly enhanced viability and functional performance when grown as spheroids. Multicellular spheroids in this aspect are ideal building units for tissue reconstruction. Here we review the current understanding of multicellular spheroid formation mechanisms, their biomedical applications, and recent advances in spheroid culture, manipulation, and analysis techniques.

The mixed coculture effect of primary rat hepatocytes and bone marrow cells is caused by soluble factors derived from bone marrow cells

Heterospheroids consisting of hepatocytes and bone marrow cells (BMCs) are formed by the mixed coculture of these cells and enhance the expression and maintenance of the liver-specific functions of hepatocytes. Not only the soluble factors derived from these cells, but also functional organoid (heterospheroid) formation, are considered to underlie this coculture effect. Therefore, in the present study, we aimed to clarify the mechanism of this co-culture effect. We performed hepatocyte monoculture with conditioned media prepared from hepatocyte cultures, BMC cultures and a coculture of hepatocytes and BMCs. When using any type of conditioned medium, no hepatocyte spheroids formed, and the hepatocytes formed a monolayer. In addition, an effect for these conditioned media was shown in terms of the albumin production and ammonia metabolism activities of the hepatocytes; conditioned medium from BMCs showed the strongest effect. The monocultured hepatocytes in the conditioned medium derived from BMCs showed equivalent albumin production and ammonia metabolism activities to the cocultured spheroids of hepatocytes and BMCs. Therefore, it was determined that the effect of the coculture of hepatocytes and BMCs was caused by soluble factors derived from BMCs.

Cultivation of hepatoma cell line HepG2 on nanoporous aluminum oxide membranes

Nanoporous aluminum oxide membranes were prepared by anodic oxidation of aluminum for application as novel cell culture substrates. Self-supporting as well as mechanically stabilized nanoporous membranes were produced from aluminum plates and micro-imprinted aluminum foils, respectively. Membranes of two different pore sizes (70 and 260 nm) were selected to investigate cellular interactions with such nanoporous substrates using cells of hepatoma cell line HepG2. The membranes express excellent cell-growth conditions. As shown by scanning electron microscopy investigations, the cells could easily adhere to the membranes and proliferate during a 4 day cell culture period. The cells exhibit normal morphology and were able to penetrate into pores with a diameter of 260 nm by small extensions (filopodia). On mechanically stabilized aluminum oxide membranes it was observed that the cells even adhere to the walls of the small cavities. It was demonstrated experimentally that the nanoporous aluminum oxide membranes are well suited as substrates in cell culture model systems for metabolic, pharmacological/toxicological research, tissue engineering and studies on pathogens as well as bioartificial liver systems.

Enhancement of liver-specific functions of primary rat hepatocytes co-cultured with bone marrow cells on tissue culture-treated polystyrene surfaces

Primary rat hepatocytes were co-cultured with bone marrow cells (BMCs) in a tissue culture-treated culture well (TCW) or a collagen-coated culture well (CCW). Although a medium containing serum was used, the co-cultured cells formed spheroids on the TCW within 2 days, and ammonia metabolism and albumin secretion activities were well maintained for 3 weeks. The co-cultured cells formed a monolayer on the CCW within 2 days, and liver functions were maintained for 3 weeks. The ammonia metabolism activities and albumin secretion activities of co-cultured cells on the CCWs were slightly inferior to those on the TCWs. This co-culture system of hepatocytes and BMCs is an appropriate culture system for the expression and maintenance of liver-specific functions in vitro, and is expected to be applicable to bioartificial liver systems, regenerative medicine, and liver function simulators.

TGF-beta1 regulation in hepatocyte-NIH3T3 co-culture is important for the enhanced hepatocyte function in 3D microenvironment

Co-culture of hepatocytes or hepatocyte spheroids with the supporting NIH3T3 in a 3D microcapsule formed with a hybrid natural/synthetic matrix has led to enhanced hepatocyte functions. We investigated the mechanism of the functional enhancement in co-culture with respect to the contributions of soluble factors and direct cell-cell interactions. The conditioned media from the co-culture induced higher P450 cytochrome oxidase activity (indicated by EROD assay) in the microencapsulated hepatocytes than the conditioned media from the NIH3T3- or the hepatocytes-alone controls. Conditioned media from physically separated co-culture of hepatocytes-NIH3T3 by a membrane insert reduced the functional enhancement. Among the known stimulators of hepatocyte functions, TGF(beta)1 is primarily responsible for the stimulation of hepatocyte functions in this 3D co-culture since the removal of TGF(beta)1 by antibody depletion eliminated the functional enhancement and the reconstitution of TGF(beta)1 restored the functional enhancement. Activation of latent TGF(beta)1 in an extracellular environment were upregulated in co-culture with no observable increase in the TGF(beta)1 expression at transcriptional and translational levels. Our data led to an improved understanding of how co-culture enhances hepatocyte functions in vitro and pave the way for further innovations in liver tissue engineering, drug metabolism studies, and other applications that require functional hepatocytes cultured in vitro.