THE BILIARY EPITHELIUM GIVES RISE TO LIVER PROGENITOR CELLS BUT MAKES A MINOR CONTRIBUTION TO HEPATOCYTE REGENERATION AFTER LIVER INJURY

We previously showed that severe liver diseases are characterized by expansion of liver progenitor cells (LPC), which correlates with disease severity. However, the origin and role of LPC in liver physiology and in the hepatic response to injury remains a contentious topic. We have now used genetic lineage tracing of Hnf1-expressing biliary duct cells to assess their contribution to LPC expansion and hepatocyte generation during normal liver homeostasis, and following different types of liver injury. We found that ductular reaction cells in human cirrhotic livers express HNF1. However, HNF1 expression was not present in newly generated EpCAM-positive hepatocytes. Using a tamoxifen-inducible Hnf1CreER/R26RYFP/LacZ mouse, we show that there is no contribution of the biliary epithelium to hepatocyte turnover during liver homeostasis in healthy mice. Moreover, after loss of liver mass, Hnf1+ LPC did not contribute to hepatocyte regeneration. We also assessed the contribution of Hnf1+ cells following acute and repeated liver injury. All animal models showed expansion of LPC, as assessed by immunostaining and gene expression profile of sorted YFP-positive cells. A contribution of Hnf1+ LPC to hepatocyte generation was not detected in animal models of liver injury with preserved hepatocyte regenerative potential such as acute acetaminophen, carbon tetrachloride injury, or chronic diethoxycarbonyl-1,4-dihydro-collidin (DDC)-diet. However, in mice fed with choline-deficient ethionine-supplemented (CDE)-diet, which causes profound hepatocyte damage and arrest, a small number of hepatocytes were derived from Hnf1+ cells. Conclusion: Hnf1+ cells do not participate in hepatocyte turnover in the healthy liver or during liver regeneration after partial hepatectomy. After liver injury, LPC arise from the biliary duct epithelium, which gives rise to a limited number of hepatocytes only when hepatocyte regeneration is compromised.

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Rodrigo-Torres D, Affò S, Coll M, Morales-Ibanez O, Millán C, Blaya D, Alvarez-Guaita A, Rentero C, Lozano JJ, Maestro MA, Solar M, Arroyo V, Caballería J, van Grunsven LA, Enrich C, Ginès P, Bataller R, Sancho-Bru P