Protein S-nitrosylation Restricts Xenobiotic Receptor PXR Hyperactivity and Ameliorates Acetaminophen-induced Liver Injury in Mice

Drug-induced liver injury (DILI), especially acetaminophen overdose, is the leading cause of acute liver failure. Pregnane X receptor (PXR) is a nuclear receptor and the master regulator of drug metabolism. Aberrant activation of PXR plays a pathogenic role in the acetaminophen hepatotoxicity. Here, we aimed to examine the PXR S-nitrosylation (SNO) in response to acetaminophen. We found that PXR was S-nitrosylated in hepatocytes and the mouse livers after exposure to acetaminophen or S-nitrosoglutathione (GSNO). Mass-spectrometry and site-directed mutagenesis identified the cysteine 307 as the primary residue for SNO-modification. In hepatocytes, SNO suppressed both agonist (rifampicin and SR12813)-induced and constitutively active PXR (VP-PXR) activations. Furthermore, in acetaminophen overdosed mouse livers, PXR protein was decreased at the centrilobular regions overlapping with increased SNO. In PXR-deficient (PXR-/-) mice, replenishing the livers with the SNO-deficient PXR significantly aggravated hepatic necrosis and apoptosis, increased HMGB1 release, and exacerbated liver injury and inflammation. Particularly, we demonstrated that S-nitrosoglutathione reductase (GSNOR) inhibitor N6022 promoted hepatoprotection by increasing the levels of PXR S-nitrosylation. In conclusion, PXR is post-translationally modified by S-nitrosylation in hepatocytes in response to acetaminophen. This modification mitigated the acetaminophen-induced PXR hyperactivity. It may serve as a new target for therapeutical intervention. Overall design: Mice were fasted for 12 h and intraperitoneal injected with freshly made acetaminophen solution (300 mg/kg) or saline. Mice were injected with acetaminophen 12 h, 24 h, 48 h, 72 h and 96 h prior to their sacrifice. Blood was collected under isoflurane anesthesia by retro-orbital bleeding. The livers were collected for protein extraction or for histopathological and immunohistological studies.