Background & aims: Stem and progenitor cells exist in normal postnatal livers. However, it has not been possible to clonally isolate or analyze postnatal liver stem/progenitor-like cells (PLSCs) derived from noninjured livers because of a lack of specific surface markers. This study aimed to establish a primary culture system for clone-sorted PLSCs.
Methods: To investigate proliferation and differentiation of PLSCs, subpopulations of nonparenchymal cells derived from noninjured livers were purified and cultured using a single-cell culture system. Cells were grown in fetal liver cell-derived conditioned medium in the presence of the Rho-associated kinase (ROCK) inhibitor Y-27632.
Results: We identified CD13 and CD133 as markers expressed on the PLSC-containing population in noninjured livers and established an efficient single-cell culture system to clonally analyze PLSCs. Culture of PLSCs is difficult, even using conditioned medium, but the addition of Y-27632 increased PLSC cell proliferation. The proportion of progenitor cells among nonparenchymal cells decreased during postnatal liver development; however, a PLSC population was still preserved in 3-month-old mice. Long-term cultivated cells derived from clone-sorted cells in normal livers were established and were called normal-liver-derived stem-like cells (NLS cells). NLS cells could differentiate into hepatocyte-like and cholangiocyte-like cells under appropriate culture conditions and underwent self-renewal-like activity in serial reclone-sorted culture. CD13 and CD133 were expressed on progenitor cells derived from fetal and postnatal liver, whereas CD49f (integrin alpha6 subunit) was strongly expressed only on PLSCs.
Conclusions: These results demonstrate the presence of progenitor cells in the CD13(+)CD49f(+)CD133(+) subpopulation of nonhematopoietic cells derived from noninjured postnatal livers.