Expression of matrix proteinases during human intrahepatic bile duct development: A possible role in biliary cell migration

Primitive biliary cells are known to migrate from the ductal plate into the mesenchyme during human intrahepatic bile duct development, and this migration process is essential for normal development of intrahepatic bile ducts. However, its molecular mechanism is unknown. Matrix proteinases play an important role in cell migration during cancer invasion and organ development. In this study, we therefore investigated in situ expression of matrix metalloproteinases (MMP) and tissue inhibitors of MMP (TIMP) during human intrahepatic bile duct development, using 32 human fetal livers. We also examined in situ expression of trypsinogen/trypsin, chymotrypsinogen/chymotrypsin, and cathepsin B, which are matrix proteinases and activators of MMP. MMP-1 expression was noted in the ductal plate and migrating primitive biliary cells. MMP-2, MMP-3, and MMP-9 were expressed in the ductal plate. TIMP-1 and TIMP-2 were expressed in the ductal plate and migrating primitive biliary cells. Trypsinogen/trypsin, chymotrypsinogen/chymotrypsin, and cathepsin B were also expressed in primitive biliary cells. These data suggest that MMP, trypsinogen/trypsin, chymotrypsinogen/chymotrypsin, and cathepsin B play a critical role in biliary cell migration during human intrahepatic bile duct development by degrading extracellular matrix proteins. The data also suggest that MMP inhibitors (TIMP-1 and TIMP-2) and MMP activators (trypsin, chymotrypsin, and cathepsin B) play an important role in biliary cell migration. The coordinated expression of MMP, MMP inhibitors, and MMP activators may be necessary for the normal development of human intrahepatic bile ducts.