The Role of O-GlcNAc in Liver Injury and Regeneration

O-GlcNAcylation is a covalent attachment of a single N-acetyl glucosamine to a serine or threonine residue of a protein. Unlike other forms of protein glycosylation, there is no chain elongation in O-GlcNAcylation. O-GlcNAc transferase (OGT) adds O-GlcNAcase (OGA) removes O-GlcNAc from a protein. The process of O-GlcNAcylation is dynamic and has extensive crosstalk with protein phosphorylation. O-GlcNAcylation plays an important role in cell cycle progression, metabolic disorders, cancer, and responses to various stressors. The role of O-GlcNAc in liver injury and regeneration has not been clearly defined. Due to the wide array of cellular processes and pathologies that involve O-GlcNAc and the knowledge gap in liver injury and regeneration, we set out to determine the role O-GlcNAc plays in liver injury and regeneration. APAP is the most widely used over-the-counter analgesic and antipyretic in the western world. Overdose of APAP leads to GSH depletion and centrilobular liver damage. First, we looked at the role of O-GlcNAc in response to APAP overdose in mice using both a decrease and an increase in O-GlcNAcylation. Hepatocyte specific deletion of OGT (OGT KO) in mice was used to decrease O-GlcNAcylation. OGT KO mice and WT mice were treated with 300 mg/kg APAP and the development of liver injury was studied over a time course of 0-24 hr. OGT KO mice showed dramatic decrease in liver injury compared to wild type mice. Serum ALT levels were markedly decreased in all timepoints in OGT KO mice and immunohistochemistry showed no centrilobular necrosis or cell death. OGT KO mice showed decrease in APAP-Cys protein adducts. There was no difference in CYP2E1 protein levels or activity and initial GSH depletion between OGT KO and WT mice. There was rapid replenishment of GSH in OGT KO mice and induction of enzyme critical to GSH biosynthesis and recycling. Treatment with Thiamet-G (TMG), a potent inhibitor of OGA, was used to model a increase in O-GlcNAcylation. C57BL/6J mice were treated acutely with 400 mg/kg TMG ...