title: Chronic hexosamine flux stimulates fatty acid oxidation by activating AMP-activated protein kinase in adipocytes.
abstract: The hexosamine biosynthesis pathway (HBP) serves as a nutrient sensor and has been implicated in the development of type 2 diabetes. We previously demonstrated that fatty acid oxidation was enhanced in transgenic mouse adipocytes, wherein the rate-limiting enzyme of the HBP, glutamine:fructose-6-phosphate amidotransferase (GFA), was overexpressed. To explore the molecular mechanism of the HBP-induced fatty acid oxidation in adipocytes, we studied AMP-activated protein kinase (AMPK), an energy sensor that stimulates fatty acid oxidation by regulating acetyl-CoA carboxylase (ACC) activity. Phosphorylation and activity of AMPK were increased in transgenic fat pads and in 3T3L1 adipocytes treated with glucosamine to stimulate hexosamine flux. Glucosamine also stimulated phosphorylation of ACC and fatty acid oxidation in 3T3L1 adipocytes, and these stimulatory effects were diminished by adenovirus-mediated expression of a dominant negative AMPK in 3T3L1 adipocytes. Conversely, blocking the HBP with a GFA inhibitor reduced AMPK activity, ACC phosphorylation, and fatty acid oxidation. These changes are not explained by alterations in the cellular AMP/ATP ratio. Further demonstrating that AMPK is regulated by the HBP, we found that AMPK was recognized by succinylated wheat germ agglutinin, which specifically binds O-GlcNAc. The levels of AMPK in succinylated wheat germ agglutinin precipitates correlated with hexosamine flux in mouse fat pads and 3T3L1 adipocytes. Moreover, removal of O-GlcNAc by hexosaminidase reduced AMPK activity. We conclude that chronically high hexosamine flux stimulates fatty acid oxidation by activating AMPK in adipocytes, in part through O-linked glycosylation.
authors.affiliation: Division of Endocrinology, University of Utah School of Medicine and Veterans Affairs Medical Center, Salt Lake City, Utah 84132, USA.
authors.forename: Bai
authors.initials: B
authors.lastname: Luo
authors.forename: Glendon J
authors.initials: GJ
authors.lastname: Parker
authors.forename: Robert C
authors.initials: RC
authors.lastname: Cooksey
authors.forename: Yudi
authors.initials: Y
authors.lastname: Soesanto
authors.forename: Mark
authors.initials: M
authors.lastname: Evans
authors.forename: Deborah
authors.initials: D
authors.lastname: Jones
authors.forename: Donald A
authors.initials: DA
authors.lastname: McClain
mesh_terms: D041721:3T3-L1 Cells; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D004789:Enzyme Activation; D005227:Fatty Acids / Q000378:metabolism*; D006031:Glycosylation; D006595:Hexosamines / Q000096:biosynthesis*; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism*; D010084:Oxidation-Reduction; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D005227:Fatty Acids; D006595:Hexosamines; D009097:Multienzyme Complexes; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase