Notch/Wnt signalling and the hepatic progenitor response in hepatocellular regeneration

Chronic liver disease remains a significant cause of morbidity and mortality globally. Transplantation is the only effective treatment for end-stage disease but is limited by organ availability, surgical complications and risks of long term immunosuppression. Novel therapies for advanced disease are therefore required. The liver has a remarkable capacity to regenerate through division of mature hepatocytes, however in chronic or severe disease hepatocyte replication fails, senescence occurs and liver failure ensues. Ductular reactions (DRs), containing hepatic progenitor cells capable of repopulating the parenchyma, arise in chronic liver injury when hepatocyte regeneration is impaired. Enhancing this endogenous repair mechanism is a key therapeutic goal. Notch and Wnt are key signals required for liver regeneration, however to date they have principally been characterised in end-point disease and the temporal kinetics of these signalling pathways not known. I sought to identify if these signals control expansion of DRs after hepatocyte injury and whether they can be therapeutically manipulated. I examined the dynamics of Notch and Wnt activity using a genetic model of hepatocellular injury and ductular-mediated regeneration whereby induction of injury could be timed, synchronising the regenerative response. Using lineage tracing, small molecules, blocking antibodies and genetic loss of function experiments I defined distinct time-sensitive Notch and Wnt signatures where early regeneration is driven by Notch and the later response by Wnt. I demonstrated that inhibition of Notch1 and Notch3 but not Notch2 reduces the generation of DRs. I identified that DRs were a source of potent growth hormone IGF1 and this production was Wnt driven. Notch driven expression of IGF1-receptor within DRs identified this axis as a node for cooperation between Notch and Wnt signals. Blocking the IGF1 axis prevented DR expansion, which conversely could be enhanced by administration of recombinant IGF1. Here, I functionally defined complex temporal dynamics controlling of DRs and identified therapeutic pathways to enhance liver regeneration

Notch-IGF1 signalling in biliary epithelial cells drives their expansion and inhibits hepatocyte differentiation

[no abstract available

Notch3 drives development and progression of cholangiocarcinoma

The prognosis of cholangiocarcinoma (CC) is dismal. Notch has been identified as a potential driver; forced exogenous overexpression of Notch1 in hepatocytes results in the formation of biliary tumors. In human disease, however, it is unknown which components of the endogenously signaling pathway are required for tumorigenesis, how these orchestrate cancer, and how they can be targeted for therapy. Here we characterize Notch in human-resected CC, a toxin-driven model in rats, and a transgenic mouse model in which p53 deletion is targeted to biliary epithelia and CC induced using the hepatocarcinogen thioacetamide. We find that across species, the atypical receptor NOTCH3 is differentially overexpressed; it is progressively up-regulated with disease development and promotes tumor cell survival via activation of PI3k-Akt. We use genetic KO studies to show that tumor growth significantly attenuates after Notch3 deletion and demonstrate signaling occurs via a noncanonical pathway independent of the mediator of classical Notch, Recombinant Signal Binding Protein for Immunoglobulin Kappa J Region (RBPJ). These data present an opportunity in this aggressive cancer to selectively target Notch, bypassing toxicities known to be RBPJ dependent

Cell lineage tracing reveals a biliary origin of intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma is a treatment refractory malignancy with a high mortality and an increasing incidence worldwide. Recent studies have observed that activation of Notch and AKT signaling within mature hepatocytes is able to induce the formation of tumors displaying biliary lineage markers, thereby raising the suggestion that it is hepatocytes, rather than cholangiocytes or hepatic progenitor cells that represent the cell of origin of this tumor. Here, we use a cholangiocyte-lineage tracing system to target p53 loss to biliary epithelia and observe the appearance of labeled biliary lineage tumors in response to chronic injury. Consequent to this, upregulation of native functional Notch signaling is observed to occur spontaneously within cholangiocytes and hepatocytes in this model as well as in human intrahepatic cholangiocarcinoma. These data prove that in the context of chronic inflammation and p53 loss, frequent occurrences in human disease, biliary epithelia are a target of transformation and an origin of intrahepatic cholangiocarcinoma