CYTOSKELETON STUDIES

POLARITY STUDIES

Hepatocyte Spheroid Self-Assembly

Cells isolated from many tissues self-organize in vitro to form multicellular structures under suitable conditions. Such a self-assembly being a manifestation of the process of tissue organization, is useful for revealing invaluable clues regarding the principles of tissue formation. The resulting self-organized structures are often shown to promote the retention of architectural and functional characteristics typical of the tissue of origin.

Studies on rat and porcine hepatocytes have demonstrated that the cytological and functional differentiation in culture are maintained and even enhanced when these cells self-assemble into round three-dimensional aggregates, or spheroids. The development of a structural configuration that resembles the native hepatic tissue concomitant with the increase in liver-specific functions is intimately related to the dynamic cytoskeletal organization. The assembly process entails specific intercellular adhesions and redistribution of cell-cell and cell-surface adhesion forces through cytoskeletal reorganization.

Hepatocytes in their native environment possess unique structural polarity in comparison to other epithelial cells. They display two or three basal surfaces as well as apical domains. The basal surface faces the liver sinusoid whereas the apical domains are specialized for carrying out specific tasks related for example to the trafficking of metabolites. The development of similar structures has been observed in hepatocyte spheroids. Tight junctions, bile-canaliculi-like structures and actin distribution similar to the native liver tissue are observed in spheroids. Characterization of the ultrastucture of hepatocyte spheroids may provide significant insight regarding hepatocyte polarization in vivo and in engineered tissue in vitro.