|dc.contributor.author||Williams, Michael John||
|dc.description.abstract||During chronic and severe acute liver injury, regeneration is thought to occur through
hepatic progenitor cells (HPCs). Understanding the regulation of HPCs may offer
therapeutic opportunities to enhance liver regeneration. HPCs are associated with an
increase in laminins in the extracellular matrix. Laminins are heterotrimeric proteins,
composed of an alpha, beta and gamma chain. There are 5 alpha chains with different
distributions and functions, but the relative contributions of these in HPC-mediated
liver regeneration are not known. My aims were to describe the laminin alpha chains
associated with the HPC response and to define the functional effects of specific
laminin chains on HPCs.
I examined the laminin alpha chains in two mouse models of HPC activation: a
transgenic model using conditional deletion of Mdm2 in hepatocytes, and a dietary
model using 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). The laminin alpha 5
(Lama5) chain is significantly upregulated in both models and forms a basement
membrane which surrounds the progenitor cells. I have also demonstrated Lama5
expression in the ductular reaction seen in human liver disease. Using primary mouse
cell cultures, I have shown that Lama5 is produced predominantly by the HPCs
themselves, rather than by stellate cells. The HPCs express the cell surface receptor
alpha-6 beta-1 integrin, a binding partner of Lama5.
I then studied the functional effects of matrix on cell behaviour in vitro using
recombinant laminins and a line of spontaneously immortalised mouse HPCs.
Compared to other laminin chains, Lama5 selectively promotes HPC adhesion and
spreading. These effects are partially blocked by antibodies against beta-1 integrin.
Lama5 also significantly enhances HPC migration, resulting in an increase in cell
migration. Furthermore, only Lama5 enhances HPC survival in serum-free medium,
with an increase in cell viability. Culturing HPCs on HPCs maintained in culture on
plastic synthesise Lama5 chain. Knock-down of endogenous Lama5 production
using siRNA results in reduced proliferation and increased hepatocytic
differentiation, with increased albumin production.
I then studied the effects in vivo using transgenic Cre-lox mouse strains that allow
conditional knock-out of either laminin alpha 5 or beta-1 integrin in HPCs. The
effects of gene deletion were examined in healthy mice and two dietary models of
HPC activation: the DDC diet and a choline-deficient, ethionine-supplemented
(CDE) diet. Although these experiments were limited by a low number of
experimental animals and low recombination rates, there was a suggestion of
impaired HPC expansion associated with loss of laminin alpha 5. There was also a
significant increase in hepatocellular injury and fibrosis in response to the DDC diet
seen with loss of laminin alpha 5 expression.
Laminin alpha 5-containing matrix is deposited around HPCs during liver
regeneration and supports progenitor cell attachment, migration and maintenance of
an undifferentiated phenotype. This work identifies a novel target for enhancing liver
|dc.contributor.sponsor||Medical Research Council (MRC)||en
|dc.publisher||The University of Edinburgh||en
|dc.relation.hasversion||WILLIAMS, M. J., CLOUSTON, A. D. & FORBES, S. J. 2014. Links between hepatic fibrosis, ductular reaction, and progenitor cell expansion. Gastroenterology, 146, 349-56.||en
|dc.subject||hepatic progenitor cells||en
|dc.title||Defining the functional role of laminin isoforms in the regulation of the adult hepatic progenitor cell||en
|dc.type||Thesis or Dissertation||en
|dc.type.qualificationname||PhD Doctor of Philosophy||en