Long-term culture of hepatic progenitors derived from mouse Dlk⁺ hepatoblasts

We previously demonstrated that hepatoblasts can be isolated from mouse fetal liver based on the expression of delta-like leucine zipper kinase (Dlk), also known as Pref-1. Each Dlk⁺ hepatoblast forms a colony containing both albumin⁺ hepatocytes and cytokeratin 19⁺ (CK19) cholangiocytic cells on either type IV collagen or laminin. Here we show that extracellular matrices (ECMs) significantly affect the growth of Dlk⁺ cells. Dlk⁺ cells vigorously proliferated on type IV collagen-coated dishes in the presence of EGF and HGF during the first 5 days, but their proliferative capability declined thereafter. Dlk⁺ cells also proliferated on laminin-coated plates and some colonies continued to expand even beyond one month after plating. These hepatic progenitor cells proliferating on laminin (HPPL) efficiently proliferated even after replating. Moreover, they were induced to differentiate into hepatocytes and cholangiocytes by overlaying Engelbreth-Holm-Swarm sarcoma (EHS) gel and by embedding in type I collagen gel, respectively. HPPL acquired the metabolic functions of accumulating polysaccharides and detoxifying ammonium ions after hepatic differentiation. Surprisingly, HPPL expressed pancreatic genes such as Pdx1 when dexamethasone was depleted from the culture medium. Therefore, the long-term culture of hepatoblasts on laminin produces multi-potential hepatic progenitors, which possess a strong proliferative capability, differentiate into both hepatocytes and cholangiocytes, and potentially give rise to pancreatic cells.