Dysregulated activation of fetal liver programme in acute liver failure

OBJECTIVE: Uncertainty about acute liver failure (ALF) pathogenesis limits therapy. We postulate that ALF results from excessive reactivation of a fetal liver programme that is induced in hepatocytes when acutely injured livers regenerate. To evaluate this hypothesis, we focused on two molecules with known oncofetal properties in the liver, Yes-associated protein-1 (YAP1) and Insulin-like growth factor-2 RNA-binding protein-3 (IGF2BP3). DESIGN: We compared normal liver with explanted livers of patients with ALF to determine if YAP1 and IGF2BP3 were induced; assessed whether these factors are upregulated when murine livers regenerate; determined if YAP1 and IGF2BP3 cooperate to activate the fetal programme in adult hepatocytes; and identified upstream signals that control these factors and thereby hepatocyte maturity during recovery from liver injury. RESULTS: Livers of patients with ALF were massively enriched with hepatocytes expressing IGF2BP3, YAP1 and other fetal markers. Less extensive, transient accumulation of similar fetal-like cells that were proliferative and capable of anchorage-independent growth occurred in mouse livers that were regenerating after acute injury. Fetal reprogramming of hepatocytes was YAP1-dependent and involved YAP1-driven reciprocal modulation of let7 microRNAs and IGF2BP3, factors that negatively regulate each other to control fate decisions in fetal cells. Directly manipulating IGF2BP3 expression controlled the fetal-like phenotype regardless of YAP1 activity, proving that IGF2BP3 is the proximal mediator of this YAP1-directed fate. CONCLUSION: After acute liver injury, hepatocytes are reprogrammed to fetal-like cells by a YAP1-dependent mechanism that differentially regulates let7 and IGF2BP3, identifying novel therapeutic targets for ALF.