Liver Progenitors Isolated from Adult Healthy Mouse Liver Efficiently Differentiate to Functional Hepatocytes In Vitro and Repopulate Liver Tissue

It has been proposed that tissue stem cells supply multiple epithelial cells in mature tissues and organs. However, it is unclear whether tissue stem cells generally contribute to cellular turnover in normal healthy organs. Here, we show that liver progenitors distinct from bipotent liver stem/progenitor cells (LPCs) persistently exist in mouse livers and potentially contribute to tissue maintenance. We found that, in addition to LPCs isolated as EpCAM+ cells, liver progenitors were enriched in CD45−TER119−CD31−EpCAM−ICAM‐1+ fraction isolated from late‐fetal and postnatal livers. ICAM‐1+ liver progenitors were abundant by 4 weeks (4W) after birth. Although their number decreased with age, ICAM‐1+ liver progenitors existed in livers beyond that stage. We established liver progenitor clones derived from ICAM‐1+ cells between 1 and 20W and found that those clones efficiently differentiated into mature hepatocytes (MHs), which secreted albumin, eliminated ammonium ion, stored glycogen, and showed cytochrome P450 activity. Even after long‐term culture, those clones kept potential to differentiate to MHs. When ICAM‐1+ clones were transplanted into nude mice after retrorsine treatment and 70% partial hepatectomy, donor cells were incorporated into liver plates and expressed hepatocyte nuclear factor 4α, CCAAT/enhancer binding protein α, and carbamoylphosphate synthetase I. Moreover, after short‐term treatment with oncostatin M, ICAM‐1+ clones could efficiently repopulate the recipient liver tissues. Our results indicate that liver progenitors that can efficiently differentiate to MHs exist in normal adult livers. Those liver progenitors could be an important source of new MHs for tissue maintenance and repair in vivo, and for regenerative medicine ex vivo. Stem Cells 2016;34:2889–2901 ICAM‐1+ hepatocytes can be isolated from healthy adult mouse liver as a distinctive cellular population from mature hepatocytes; they are small, mononucleated hepatocytes and express Cyps at a lower level. ICAM‐1+ cells proliferate for long‐term in vitro and keep potential to differentiate into functional hepatocytes. When they are used for transplantation, ICAM‐1+ cells are integrated to the recipient liver tissue as mature hepatocytes. ICAM‐1+ hepatocytes could be a promising cellular source for generating functional hepatocytes ex vivo.