Expression of α-fetoprotein and stem cell factor/c-kit system in bile duct ligated young rats

The existence of a facultative hepatic stem cell compartment in bile ductules that participates in the renewal process of epithelial cell populations in the liver is well documented. The present study was undertaken to determine whether the immature bile epithelium responds differently to growth stimulus induced by bile stasis to that seen in the adult animal. In addition, the possible involvement of the growth factor/receptor systems associated with early activation of hepatic stem cells in bile duct proliferation was also examined. Bile duct ligation was used to induce the proliferation of bile epithelial cells. The expression of full-length alpha-fetoprotein (AFP) was used as an indicator for activation of the stem cell compartment. AFP was highly and selectively expressed in small bile ducts 7 days after bile duct ligation in immature rats up to 5 weeks of age. Although no significant increase in the expression of stem cell factor (SCF) c-kit, hepatocyte growth factor (HGF), and transforming growth factor-α (TGF-α) was observed 7 days after bile duct ligation in adult rats, the expression of all these growth factors was increased in bile duct ligated rats up to 5 weeks of age. These results suggest that the bile ductular epithelium in the young rats responds to bile stasis in a fashion that is phenotypically similar to that seen during early activation of hepatic stem cells in adult liver.