Abstract

Stem cells, regeneration and organoid cultures

Meritxell Huch(1,2,3)

1: Gurdon Institute-Wellcome Trust/ Cancer Research UK, CB2 1QN United Kingdom 2: Department of Physiology, Developmental Biology and Neuroscience, University of Cambridge, 3: the Wellcome Trust-Medical Research Council Stem Cell Institute

We reported that mouse liver organoids indefinitely expanded in vitro (for >1 year), in the absence of a mesenchymal niche. The cultured cells expressed ductal markers and differentiated into functional hepatocytes in vitro and in vivo, following transplantation. We further developed our culture system to study human liver biology and disease. Hence, human liver organoids from liver donor tissue expand long term in culture while maintaining their differentiation potential and genetic stability in vitro. Recently we demonstrated the applicability of this system to study human liver cancer in vitro. We established the first human liver cancer organoid culture system for both hepatocellular carcinoma as well as cholangiocarcinoma resected material, and demonstrated its applicability for disease modeling and drug testing. Here, we discuss the use of this liver organoid technology to underscore biological principles of adult liver regeneration. Upon severe or chronic liver injury, differentiated adult liver cholangiocytes (ductal cells) become activated and proliferate extensively to restore the tissue, by generating both hepatocytes and ductal cells. However, the molecular mechanism behind the activation of ductal cells remains largely unknown. Here we report that our organoid culture system enables the activation of adult differentiated liver ductal cells into bi-potent liver progenitors, hence providing a platform where to study regeneration in a dish. Using this liver organoid system we have found that the transition from the ductal differentiated state to an active proliferating progenitor state involves a massive, yet transient, epigenetic reprogramming where active DNA -demethylation plays an important role in order to activate the progenitor program and successfully establish self-renewing liver organoid cultures.