Fabrication of a fiber-type hepatic tissue by bottom-up method using multilayer spheroids

Liver regenerative medicine, a therapy using cultured hepatocytes or hepatic tissues, has the potential to replace liver transplantation. However, this therapeutic strategy has challenges to overcome, including in construction of the hepatic tissues. As an approach to fabricating functional 3D hepatic tissues, we focused on hepatocyte spheroids, which have high cell density and maintain high liver-specific functions. We employed a bottom-up method using spheroids, arranging hepatocytes and endothelial cells regularly at the time of tissue construction. This enabled a vascular network to be formed within the three-dimensional hepatic tissue. We included NIH/3T3 cells, known to promote vasculature formation by endothelial cells. We fabricated hepatocyte spheroids covered with human umbilical vein endothelial cells (HUVECs) and NIH/3T3 cells (EC-3T3-covered hepatocyte spheroids) and constructed the hepatic tissues by stacking these cell types in hollow fibers. We then performed histological and functional analyses of the resulting hepatic tissues. The hepatic tissues constructed by stacking EC-3T3-covered hepatocyte spheroids showed high liver-specific functions; that is, ammonia removal and albumin secretion. The HUVECs formed endothelial networks. In addition, hypoxia-inducible factor-1α (HIF-1α) expression was suppressed in the hepatic tissue throughout the culture period and the hepatic tissue was sufficiently strong for use in certain analyses and applications. In summary, we fabricated a functional 3D hepatic tissue by the bottom-up method using hepatocyte spheroids covered with HUVECs and NIH/3T3 cells.