Sox9 as a tool to modulate liver progenitor cell (LPC) - driven liver regeneration

Details

Supervisors

Leclercq, Isabelle

Faculty

Faculté de pharmacie et des sciences biomédicales

Degree label

Master [120] en sciences biomédicales, à finalité approfondie

Abstract

The liver has a high capacity for self-renewal. When a majority of its mass is surgically removed, a procedure called partial hepatectomy, the proliferation of hepatocytes allows the liver to recover its lost mass. However, in chronic liver injuries, hepatocytes are no longer able to proliferate. In this situation occurs the ductular reaction (DR), characterised by reactive proliferation of small immature cells of biliary origin invading the liver parenchyma. Within the DR cells lies a cell subpopulation called the liver progenitor cells (LPC) with the potential to differentiate into hepatocytes. Unfortunately, the LPC-driven regeneration is poorly efficient and its extent is limited hence liver failure occurs. Sox9 is a transcription factor that maintain the biliary cells in their biliary phenotype and prevents their differentiation into hepatocytes. Here, we want to evaluate whether the inhibition or the loss of Sox9, will unlock LPC, promote LPC to hepatocyte differentiation and increase the pool of functional hepatocytes in models of chronic liver injury. To inhibit Sox9 expression we targeted EGFR signaling pathway, known to control Sox9 expression. We used the pharmacological EGFR inhibitor Erlotinib and a choline-deficient, L-amino-acid defined high fat diet (CDAA-HFD) as a model of DR associated to steatohepatitis in OPNiCreERT2/+:ROSA26YFP/YFP for biliary cells lineage tracing. The CDAA-HFD causes ductular reaction and LPC-driven regeneration, easily identified by the expression of the yellow fluorescent protein (YFP) in some hepatocytes. The YFP-stained area and fibrosis were comparable between controls and Erlotinib treated mice. These observations conclude that Erlotinib treatment did not enhance LPC-mediated regeneration. To specifically delete Sox9 gene expression in cholangiocytes as well as mark them we used triple transgenic OPNiCreERT2/+:ROSA26YFP/+;Sox9fl/fl mice. Compared to control groups, after Tamoxifen-induced recombination, we observed a cholangiocyte specific Sox9 deletion in mice homozygous for the Sox9 floxed allele. In order to analyse LPC-mediated regeneration, mice were repeatedly exposed to CCl4 to cause chronic centrilobular necrosis. We hypothesized that the deletion of Sox9 in cholangiocytes would increase LPC differentiation into hepatocytes and increase the pool of functional hepatocytes. To asses the number of differentiation events we quantified the number of YFP+ patches and the number of CK19+ DR cells. There were no differences in the number of YFP+ patches; however, we observed a reduction in the area of DR cells in the Sox9-deleted groups. Although the number of DRs is decreased, we observed a similar number of DR-derived patches, suggesting that deletion of Sox9 increases the differentiation of LPC into hepatocytes.