Reconstruction of hepatic tissue in vitro

Abstract

It is still difficult to make primary hepatocytes function in ex vivo environment as similar as they do in vivo. Primary hepatocytes immediately lose their highly differentiated functions in vitro. For example, many cytochrome P450s lose their activity within 24 hours after isolation. Therefore, the researches using primary hepatocytes have been performed to the development of methods either to maintain the inherently highly differentiated functions or to achieve vigorous proliferative capacity. However, It has been considered to be complicated to recover the differentiated functions and to grow primary hepatocytes in vitro.

　Although mature hepatocytes have been thought to be uniform cells, in the 2010s their heterogeneity has been reported by many laboratories based on studies in mice using the lineage tracing method. The existence of hepatocytes possessing high proliferative potential, which are named as small hepatocytes (SHs), was found (Mitaka T et al. Hepatology 1992). Differentiated functions of hepatocytes have been thought to be reciprocally related to their growth, whereas SHs can grow to form colonies and to increase their differentiated function with time in culture. When SHs interact with stellate cells, both cells secrete extracellular matrix to form a basement membrane-like structure under the colony. Then, SHs autonomously stop growing and enlarge their cytoplasm. Matured SHs acquire the polarity and form bile canaliculi (BCs) between cells. Secreted bile into BCs is transported in a certain direction. Recently, we have succeeded to connect BCs with bile ducts (BDs) in co-culturing SHs with bile duct cells, thereby guiding the bile secreted by hepatocytes into BDs (Tanimizu N et al. Nat Commun 2021).

In this symposium, I will talk how cell morphology, extracellular matrix, nonparenchymal cells and bile duct cells affect the proliferation and the function of cultured hepatocytes.