Downregulation of miR122 by grainyhead-like 2 restricts the hepatocytic differentiation potential of adult liver progenitor cells

摘要

Late fetal and adult livers are reported to contain bipotential liver stem/progenitor cells (LPCs), which share surface markers, including epithelial cell adhesion molecule (EpCAM), with cholangiocytes and differentiate into both hepatocytes and cholangiocytes. However, recent results do not necessarily support the idea that LPCs contribute significantly to cellular turnover and regeneration by supplying new hepatocytes. Here, we examined the colony-forming capability of EpCAM(+) cells isolated from mouse livers between E17 and 11 weeks of age. We found that the number of bipotential colonies was greatly reduced between 1 and 6 weeks, indicating that the number of LPCs decreases during postnatal development. Moreover, bipotential colonies derived from adult LPCs contained substantially fewer albumin(+) cells than those from neonatal LPCs. We further examined the differentiation potential of neonatal and adult LPCs by transplantation and found that neonatal cells differentiated into mature hepatocytes in recipient livers more frequently than adult LPCs. Since we previously reported that the transcription factor grainyhead-like 2 (GRHL2) expressed in EpCAM(+) cells inhibits hepatocytic differentiation, we examined whether targets of GRHL2 might block hepatocytic differentiation. DNA and microRNA microarrays revealed that miR122, the expression of which correlates with hepatocytic differentiation, was greatly reduced in adult as compared with neonatal EpCAM(+) cells. Indeed, GRHL2 negatively regulates the promoter/enhancer activity of the Mir122 gene. Our results indicate that neonatal but not adult EpCAM(+) LPCs have great potential to produce albumin(+) hepatocytes. GRHL2 suppresses transcription of miR122 and thereby restricts the differentiation potential of adult LPCs.