NARUSE Katsutoshi University of Tokyo, Faculty of Medicine, 医学部附属病院, 助手 (50291323)
MIKI Kenji University of Tokyo, Faculty of Medicine, 医学部附属病院, 助手 (10242059)
MAKUUCHI Masatoshi University of Tokyo, Faculty of Medicine, Professor, 医学部附属病院, 教授 (60114641)
WATANABE Yoshihiro Nihon University, School of Medicine, Assistant Professor, 医学部, 講師 (20240533)
KATO Komei Nihon University, School of Medicine, Assistant Professor, 医学部, 講師 (40233788)
Background/Aim : The plasticity of bone marrow cells (BMCs) is shown by their ability to differentiate into mesenchymal as well as endodermal and ectodermal lineages. Transdifferentiation of BMCs into hepatocytes has also been demonstrated, both in vitro and in vivo. At first, we investigated the effects of liver nonparenchymal cells (NPCs) and sera from liver failure patients (HSLF) on the in vitro transdifferentiation of murine BMCs into hepatocytes. Next, we investigated the mechanisms underlying transdifferentiation of BMCs into hepatocytes processes. We have focused on the initial events occurring in bone marrow in response to liver injury.
Methods : Liver NPCs from wild type mice, and 5-azacytidine-treated BMCs from green fluorescence protein transgenic mice, were cocultured in medium containing HSLF in combination with several cytokines. Hepatocyte-specific gene expression in BMCs was identified by immunocytochemistry and RT-PCR. Next, mice were given 2-acetyl aminofluorene (AAF)
intraperitonealy for one, week, followed by two-thirds partial hepatectomy. Other mice underwent hepatectomy without AAF administration. Hepatic and endodermal differentiation of bone marrow cells was evaluated by measuring hepatocyte-related gene expression by real time RT-PCR before and after hepatectomy.
Results : Bone marrow cell-derived hepatocyte-like colonies appeared after several days of coculture in medium containing HSLF, oncostatin M (OSM) and hepatocyte growth factor (HGF). These colonies expressed hepatocyte-specific genes. Transdifferentiation was enhanced by 5-azacytidine treatment, and by HSLF, OSM and HGF. It did not take place when the BMCs were separated, from the NPCs in a dual chamber dish, or cultured with other mesenchymal cells. Partial hepatectomy induced expression of several early hepatic genes such as alpha-fetoprotein (AFP) and hepatocyte nuclear factor 3. Expression of these genes was enhanced by the administration of AAF. We identify the sub-population of bone marrow cells responsible for transdifferentiation in the Lin, CD34^+, c-kit^+, Sca-1^+, CD49f^+ and CD45^+ fractions, corresponding to hematopoietic progenitors.
Conclusions : Direct interaction of murine BMCs with liver NPCs, as well as soluble factors in the HSLF and a demethylating agent, strongly stimulate transdifferentiation into hepatocytes. Early endodermal and hepatic differentiation occurs in bone marrow in response to hepatectomy, especially when regeneration of the remnant liver is suppressed. Circulating signals generated by severe liver injury may stimulate this differentiation. Less