Biology subjects

Hanover, J. A.

Publications and source records attributed to Hanover, J. A..

4 recordsLinked to original sources

bioRxiv2023

The Essential Role of O-GlcNAcylation in Hepatic Differentiation

Background & AimsO-GlcNAcylation is a post-translational modification catalyzed by the enzyme O-GlcNAc transferase (OGT), which transfers a single N-acetylglucosamine sugar from UDP-GlcNAc to the protein on serine and threonine residues on proteins. Another enzyme, O-GlcNAcase (OGA), removes this modification. O-GlcNAcylation plays an important role in pathophysiology. Here, we report that O-GlcNAcylation is essential for hepatocyte differentiation, and chronic loss results in fibrosis and hepatocellular carcinoma. MethodsSingle-cell RNA-sequencing was used to investigate hepatocyte differentiation in hepatocyte-specific OGT-KO mice with increased hepatic O-GlcNAcylation and in OGA-KO mice with decreased O-GlcNAcylation in hepatocytes. HCC patient samples and the DEN-induced hepatocellular carcinoma (HCC) model were used to investigate the effect of modulation of O-GlcNAcylation on the development of liver cancer. ResultsLoss of hepatic O-GlcNAcylation resulted in disruption of liver zonation. Periportal hepatocytes were the most affected by loss of differentiation characterized by dysregulation of glycogen storage and glucose production. OGT-KO mice exacerbated DEN-induced HCC development with increased inflammation, fibrosis, and YAP signaling. Consistently, OGA-KO mice with increased hepatic O-GlcNAcylation inhibited DEN-induced HCC. A progressive loss of O-GlcNAcylation was observed in HCC patients. ConclusionsOur study shows that O-GlcNAcylation is a critical regulator of hepatic differentiation, and loss of O-GlcNAcylation promotes hepatocarcinogenesis. These data highlight increasing O-GlcNAcylation as a potential therapy in chronic liver diseases, including HCC. Lay SummaryProteins in cells are modified by the addition of a single glucosamine sugar molecule called O-GlcNAcylation. Loss of O-GlcNAcylation in hepatocytes, the most common type of cells in the liver, causes the liver to lose its function and can result in increased liver diseases such as fibrosis and cancer. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=85 SRC="FIGDIR/small/528884v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@aed343org.highwire.dtl.DTLVardef@1b00966org.highwire.dtl.DTLVardef@391ef9org.highwire.dtl.DTLVardef@206d8c_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LISingle-Cell RNA-sequencing reveals loss of metabolic liver zonation in O-GlcNAcylation deficient livers. C_LIO_LILoss of O-GlcNAcylation promoted DEN-Induced HCC. C_LIO_LIIncrease of hepatic O-GlcNAcylation prevented HCC progression. C_LI

pathology↗

bioRxiv2022

O-GlcNAc transferase plays a non-catalytic role in C. elegans male fertility

Animal behavior is influenced by the competing drives to maintain energy and to reproduce. The balance between these evolutionary pressures and how nutrient signaling pathways intersect with mating drive remains unclear. The nutrient sensor O-GlcNAc transferase, which post-translationally modifies intracellular proteins with a single monosaccharide, is responsive to cellular nutrient status and regulates diverse biological processes. Though essential in most metazoans, O-GlcNAc transferase (ogt-1) is dispensable in Caenorhabditis elegans, allowing genetic analysis of its physiological roles. Compared to control, ogt-1 males have a four-fold reduction in mean offspring, with nearly two thirds producing zero progeny. Interestingly, we found that isolated ogt-1 males are less likely to engage in mate-searching, and they initiate mating less often when exposed to mates. In addition, ogt-1 males which do initiate mating are less likely to continue with subsequent steps in the mating process, resulting in fewer successful sperm transfers. Lowering barriers to mating such as immobilizing mates or allowing more mating time significantly improves ogt-1 male mating. Surprisingly, we found high fertility levels for ogt-1 mutant males with hypodermal expression of wild-type ogt-1 and by ogt-1 harboring mutations that prevent the transfer of O-GlcNAc by OGT-1. This suggests OGT-1 serves a non-catalytic function in the hypodermis impacting the male mating drive. This study builds upon research on the nutrient sensor O- GlcNAc transferase and demonstrates a role it plays in the interplay between the evolutionary drives for reproduction and survival. Author SummaryAnimals must make decisions on whether to engage in reproduction or conserve energy. These decisions must take into account the energy available to the animal, therefore making the nutrient sensing enzyme OGT of particular interest. In response to nutrient levels in the cell, OGT transfers the GlcNAc sugar onto proteins to regulate their function. OGT is implicated in a number of human diseases including diabetes, cancer, and X-linked intellectual disability. By deleting the gene encoding OGT in the nematode C. elegans, we show OGT is required for male fertility. We assessed the behavior of these mutant male worms and found they have a reduced mating drive. Surprisingly, restoring OGT specifically in the hypodermis was able to raise male fertility and mating drive back to normal levels. In addition, missense mutations in the OGT catalytic domain which prevent the enzyme from transferring GlcNAc do not negatively impact fertility, suggesting a different function of OGT is important in this process. Our study demonstrates that OGT is important in critical behavioral decisions and that further investigation in C. elegans may help reveal new functions of the enzyme.

genetics↗

bioRxiv2021

Regulation of Liver Regeneration by hepatocyte O-GlcNAcylation in mice

The liver has a unique capacity to regenerate after injury in a highly orchestrated and regulated manner. Here we report that O-GlcNAcylation, an intracellular post-translational modification (PTM) regulated by two enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), is a critical termination signal for liver regeneration (LR) following partial hepatectomy (PHX). We studied liver regeneration after PHX on hepatocyte specific OGT and OGA knockout mice (OGT-KO and OGA-KO), which caused a significant decrease (OGT-KO) and increase (OGA-KO) in hepatic O-GlcNAcylation, respectively. OGA-KO mice had normal regeneration, but the OGT-KO mice exhibited substantial defects in termination of liver regeneration with increased liver injury, sustained cell proliferation resulting in significant hepatomegaly, hepatic dysplasia and appearance of small nodules at 28 days after PHX. This was accompanied by a sustained increase in expression of cyclins along with significant induction in pro-inflammatory and pro-fibrotic gene expression in the OGT-KO livers. RNA-Seq studies revealed inactivation of hepatocyte nuclear 4 alpha (HNF4), the master regulator of hepatic differentiation and a known termination signal, in OGT-KO mice at 28 days after PHX, which was confirmed by both Western blot and IHC analysis. Furthermore, a significant decrease in HNF target genes was observed in OGT-KO mice, indicating a lack of hepatocyte differentiation following decreased hepatic O-GlcNAcylation. Immunoprecipitation experiments revealed HNF4 is O-GlcNAcylated in normal differentiated hepatocytes. These studies show that O-GlcNAcylation plays a critical role in the termination of LR via regulation of HNF4 in hepatocytes. Layman summaryO-GlcNAcylation is a protein modification that plays a critical role in various biological processes including cell proliferation, differentiation, and disease progression. These studies show that O-GlcNAcylation in hepatocytes is essential for proper liver regeneration. Without O-GlcNAcylation, hepatocytes keep on proliferating eventually forming liver tumors.

pathology↗

bioRxiv2021

Nutrient Responsive O-GlcNAcylation Dynamically Modulates Galectin 3 Secretion

Endomembrane glycosylation and cytoplasmic O-GlcNAcylation each play essential roles in nutrient sensing, and in fact, characteristic changes in glycan patterns have been described in disease states such as diabetes and cancer. These changes in glycosylation have important functional roles and can drive disease progression. However, little is known about the molecular mechanisms underlying how these signals are integrated and transduced into biological effects. Galectins are proteins that bind glycans that are secreted by a poorly characterized non-classical secretory mechanism. Once outside the cell, galectins bind to terminal galactose residues of cell surface glycans and modulate numerous extracellular functions like clathrin independent endocytosis (CIE). Originating in the cytoplasm, galectins are predicted substrates for O-GlcNAc addition and removal. This study shows that galectin 3 is O-GlcNAcylated, and that changes in O-GlcNAc cycling alters its secretion. Moreover, we determined that there is a significant difference in O-GlcNAcylation status between cytoplasmic and secreted galectin 3. We observed dramatic alterations in galectin 3 secretion in response to nutrient conditions and that these changes were dependent on dynamic O-GlcNAcylation. Finally, we showed that alterations in galectin 3 secretion via disrupted O-GlcNAcylation drove changes in CIE. These results indicate that dynamic O-GlcNAcylation of galectin 3 plays a role in modulating its secretion and can tune its function of transducing nutrient sensing information coded in cell surface glycosylation into biological effects.

cell biology↗