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Background and Aims:The Notch Signalling pathway plays a critical role
in hepatic development, particularly in the specification of cholangiocytes
from both Dlk+ hepatoblasts in vitro and the correct patterning of the
biliary tree in vivo. During severe hepatic damage Hepatic Progenitor
Cells (HPCs) expand from the canals of Hering, migrate from these niche
positions into the parenchyma and are capable of repair. It has been shown
by us and others that the oval cells reside in a definitive niche where they
are intimately associated with a laminin matrix as well as hepatic fibroblasts and macrophages. Notch involvement in embryonic development and
hepatocellular proliferation implies that analogous mechanisms may be
involved in HPC mediated regeneration.

Methods: PC induction was achieved in mice through administering CDE
or DDC dietary regimens. Analysis of Notch components was performed
through western blot, qPCR and immunohistochemistry. in vitro and in vivo
inhibition studies were performed using DAPT to inhibit Notch activation.
Freshly isolated panCK+ HPCs were enriched for by a differential percoll
gradient and MACS CD45 depletion and were studied in cholangiocyte
and hepatocyte differentiation protocols in the presence of a laminin matrix
for the effects of Notch signalling.

Results: HPCs are intimately contacted by F4/80+ macrophages and
Thy-1+ hepatic fibroblasts in vivo. Isolated macrophages and fibroblasts
show high levels of Jag1 expression through western blot, qPCR and
F-IHC. Notch4 is expressed in small cells migrating from the biliary
tree into the damaged parenchyma. Differentiation of isolated HPCs into
cholangiocytes and hepatocytes depended upon Notch signalling. Notch
inhibition with DAPT significantly reduces the number of cholangiocytes
spontaneously arising in culture from 36% to 14% of total cells (P0.03)
without altering the number of Albumin+ hepatocytes.

Conclusions: Notch pathway ligands are expressed within the HPC cell
niche with receptor in the oval cells themselves. Notch signalling plays a
role in the lineage commitment of Hepatic Progenitor Cells and appears
to be required for the specification of cholangiocytes in vitro. These data
show Notch signalling is not only vital for liver development but for
defining the fate of HPCs following chronic liver injury
Original languageEnglish
Pages (from-to)S305-S305
Number of pages1
JournalJournal of Hepatology
Issue numberSupplement 1
Publication statusPublished - Apr 2009

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