Role of HIF1α in FXR-mediated protection and anti-inflammatory macrophage polarization in parenteral nutrition-associated cholestasis.

Parenteral nutrition-associated cholestasis (PNAC) arises from suppressed FXR signaling and macrophage activation driven by intestinal LPS and PN-derived phytosterols. We investigated whether tissue hypoxia and HIF1α signaling play a role in FXR-mediated protection in PNAC. PNAC mouse intrahepatic mononuclear cells (IHMCs) displayed evidence of hypoxia and upregulation of HIF1α and hypoxia-responsive genes, also demonstrated in livers from human infants with PNAC. Myeloid-specific Hif1a knock-out reduced liver injury, decreased macrophage infiltration, restored FXR signaling, and promoted anti-inflammatory gene expression in PNAC mice. HIF1α physically interacted with the histone methyltransferase enzyme, EZH2 in PNAC liver, an effect disrupted by FXR agonist GW4064, which modified EZH2 phosphorylation by activating AMPK/AKT kinases, diminishing H3K27me3 repression at anti-inflammatory loci. Furthermore, GW4064 reduced pro-inflammatory gene expression while inducing anti-inflammatory genes in IHMCs, decreased hepatocyte apoptosis, and enhanced HIF1α/H19 interaction. Inhibition of EZH2 with Tazemetostat reduced liver injury by decreasing pro-inflammatory markers. In conclusion, HIF1α-EZH2 signaling promoted hepatic inflammation and injury in PNAC, and FXR activation counteracted this axis to promote anti-inflammatory macrophage polarization.