Retinoic acid generates a beneficial microenvironment for liver progenitor cell activation in acute liver failure

Objective When massive necrosis occurs in acute liver failure (ALF), rapid expansion of hepatic stem cells called liver progenitor cells (LPC) in a process called ductular reaction (DR) is required for survival. The exact underlying mechanisms of this process are not known to date. In ALF, high levels of retinoic acid (RA), a molecule known for its pleiotropic roles in embryonic development, are secreted by activated hepatic stellate cells (HSCs). We hypothesized that RA plays a key role during DR in ALF.

RNA-Seq was performed to identify molecular signaling pathways affected by all-trans retinoid acid (atRA) treatment in HepaRG LPC cells. Functional assays for RA were performed in HepaRG cells with atRA treatment as well as co-culture with LX-2 cells in vitro, and liver tissue of patients suffering from ALF in vivo.

Under ALF conditions, activated HSCs secreted RA, inducing RARα nuclear translocation in LPCs. RNA-seq data and investigations in HepaRG cells revealed that atRA treatment activated the WNT-β-Catenin pathway, enhanced stemness genes (SOX9, AFP, et.al), promoted energy storage, and elevated the expression of ATP-binding cassette (ABC) transporters depending on RARα nuclear translocation. Further, atRA treatment-induced pathways were confirmed in a co-culture system of HepaRG with LX-2 cells. Patients with ALF who displayed RARα nuclear translocation in LPC had significantly better MELD scores than those without.

In ALF, RA secreted by activated hepatic stellate cells promotes LPC activation, a prerequisite for subsequent LPC-mediated liver regeneration. Competing Interest Statement The authors have declared no competing interest. Abbreviations - ABC - ATP-binding cassette - ACAA1 - acetyl-CoA acyltransferase 1 - ACSL5 - acyl-CoA synthetase long chain family member 5 - AFP - alpha fetoprotein - ALF - acute liver failure - APOA1 - apolipoprotein A1 - α-SMA - Alpha-smooth muscle actin - ATRA - all-trans retinoid acid - CEBP - CCAAT enhancer binding protein - CK7/19 - Cytokeratin 7/19 - COL1A1 - Collagen, type I, alpha 1 - CPT1B - palmitoyltransferase 1B - GATA6 - GATA binding protein 6 - HSC - hepatic stellate cell - IF - immunofluorescence - IHC - immunohistochemistry - INR - international normalized ratio - LPC - liver progenitor cell - LPL - lipoprotein lipase - LTx - liver transplantation - MELD - Model for End-Stage Liver Disease - MHN - Massive hepatic necrosis - MMP2/9 - matrix metalloproteinase 2/9 - PLIN1/5 - perilipin 1/5 - phHSC - primary human hepatic stellate cell - POLK - DNA polymerase kappa - RAR - retinoic acid receptor - RXR - retinoid X receptor - SOX9 - SRY-box transcription factor 9 - TBIL - total bilirubin - TGF-β1 - transforming growth factor-β1 - ULN - upper limit of normal