IMPORTANCE OF CELL-AGGREGATION FOR EXPRESSION OF LIVER FUNCTIONS AND REGENERATION DEMONSTRATED WITH PRIMARY CULTURED-HEPATOCYTES

Adult rat hepatocytes aggregated to form floating multicellular spheroids when cultured in Primaria dishes, which have a positively charged surface, in serum-free Williams' medium E (WE) supplemented with insulin and epidermal growth factor (EGF). These hormones were essential for maintenance of the spheroids, whereas the size of the spheroids depended on the inoculum cell density. The spheroids retained in vivo levels of expressions of albumin and glucokinase and synthesized scarcely any DNA even in the presence of insulin and EGF. On transfer to type I collagen-coated dishes, the spheroids gradually disaggregated and the cells formed monolayers, in which the expressions of albumin and glucokinase were suppressed and DNA synthesis and hexokinase activity were increased. DNA synthesis of hepatocytes in monolayer culture was maximal 24 hr after transfer of the spheroids, approximately 80% of the hepatocyte nuclei were labelled with bromodeoxyuridine during culture for 48 hr, and the mitotic index was approximately 70% after 60 hr. These results suggest that, in spheroids, hepatocytes remained in the G, phase, but that when they formed monolayers, they progressed to the G1 phase and proceeded through the cell cycle in the presence of insulin and EGF. This work shows that the cell cycle of hepatocytes in culture can be manipulated by providing conditions for quiescence as spheroids or growth as monolayers and that the shape of hepatocytes is important for regulating their growth and liver-specific functions. (C) 1993 Wiley-Liss, Inc.