RESUMEN
Nuclear receptors including Aryl hydrocarbon Receptor (AhR), Constitutive Androstane Receptor (CAR), Pregnane X Receptor (PXR), and Peroxisome Proliferator-Activated Receptor-alpha (PPARα) function as xenobiotic sensors. Hepatocyte nuclear factor 4alpha (HNF4α) is a highly conserved orphan nuclear receptor essential for liver function. We tested the hypothesis that HNF4α is essential for function of these four major xenosensors. Wild-type (WT) and hepatocyte-specific HNF4α knockout (HNF4α-KO) mice were treated with the mouse-specific activators of AhR (TCDD, 30 µg/kg), CAR (TCPOBOP, 2.5 µg/g), PXR, (PCN, 100 µg/g), and PPARα (WY-14643, 1 mg/kg). Blood and liver tissue samples were collected to study nuclear receptor activation. TCDD (AhR agonist) treatment did not affect the liver-to-body weight ratio (LW/BW) in either WT or HNF4α-KO mice. Further, TCDD activated AhR in both WT and HNF4-KO mice, confirmed by increase in expression of its target genes. TCPOBOP (CAR agonist) significantly increased the LW/BW ratio and CAR target gene expression in WT mice, but not in HNF4α-KO mice. PCN (a mouse PXR agonist) significantly increased LW/BW ratio in both WT and HNF4α-KO mice however, it failed to induce PXR target genes in HNF4 KO mice. The treatment of WY-14643 (PPARα agonist) increased LW/BW ratio and PPARα target gene expression in WT mice but not in HNF4α-KO mice. Together, these data indicate that the function of CAR, PXR, and PPARα but not of AhR was disrupted in HNF4α-KO mice. These results demonstrate that HNF4α function is critical for the activation of hepatic xenosensors, which are critical for toxicological responses.
RESUMEN
Overdose of acetaminophen (APAP) is the major cause of acute liver failure (ALF) in the Western world with very limited treatment options. Previous studies from our groups and others have shown that timely activation of liver regeneration is a critical determinant of transplant-free survival of APAP-induced ALF patients. Here, we report that hepatocyte-specific deletion of Yes-associated protein (Yap), the downstream mediator of the Hippo Kinase signaling pathway results in faster recovery from APAP-induced acute liver injury. Initial studies performed with male C57BL/6J mice showed a rapid activation of Yap and its target genes within first 24 h after APAP administration. Treatment of hepatocyte-specific Yap knockout (Yap-KO) mice with 300 mg/kg APAP resulted in equal initial liver injury but a significantly accelerated recovery in Yap-KO mice. The recovery was accompanied by significantly rapid hepatocyte proliferation supported by faster activation of Wnt/ß-catenin pathway. Furthermore, Yap-KO mice had significantly earlier and higher pro-regenerative inflammatory response following APAP overdose. Global gene expression analysis indicated that Yap-KO mice had a robust activation of transcription factors involved in response to endoplasmic reticulum stress (XBP1) and maintaining hepatocyte differentiation (HNF4α). In conclusion, these data indicate that inhibition of Yap in hepatocytes results in rapid recovery from APAP overdose due to an earlier activation of liver regeneration.