title: Inhibited insulin signaling in mouse hepatocytes is associated with increased phosphatidic acid but not diacylglycerol.
abstract: Although an elevated triacylglycerol content in non-adipose tissues is often associated with insulin resistance, the mechanistic relationship remains unclear. The data support roles for intermediates in the glycerol-3-phosphate pathway of triacylglycerol synthesis: diacylglycerol (DAG), which may cause insulin resistance in liver by activating PKCϵ, and phosphatidic acid (PA), which inhibits insulin action in hepatocytes by disrupting the assembly of mTOR and rictor. To determine whether increases in DAG and PA impair insulin signaling when produced by pathways other than that of de novo synthesis, we examined primary mouse hepatocytes after enzymatically manipulating the cellular content of DAG or PA. Overexpressing phospholipase D1 or phospholipase D2 inhibited insulin signaling and was accompanied by an elevated cellular content of total PA, without a change in total DAG. Overexpression of diacylglycerol kinase-θ inhibited insulin signaling and was accompanied by an elevated cellular content of total PA and a decreased cellular content of total DAG. Overexpressing glycerol-3-phosphate acyltransferase-1 or -4 inhibited insulin signaling and increased the cellular content of both PA and DAG. Insulin signaling impairment caused by overexpression of phospholipase D1/D2 or diacylglycerol kinase-θ was always accompanied by disassociation of mTOR/rictor and reduction of mTORC2 kinase activity. However, although the protein ratio of membrane to cytosolic PKCϵ increased, PKC activity itself was unaltered. These data suggest that PA, but not DAG, is associated with impaired insulin action in mouse hepatocytes.
authors.affiliation: From the Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Chongben
authors.initials: C
authors.lastname: Zhang
authors.affiliation: From the Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Gwen
authors.initials: G
authors.lastname: Hwarng
authors.affiliation: From the Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Cooper
authors.affiliation: From the Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Trisha J
authors.initials: TJ
authors.lastname: Grevengoed
authors.affiliation: the Department of Pharmacology, University of Virginia Health System, Charlottesville, Virginia 22908, and.
authors.forename: James M
authors.initials: JM
authors.lastname: Eaton
authors.affiliation: the Departments of Pharmacology & Medicine, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612.
authors.forename: Viswanathan
authors.initials: V
authors.lastname: Natarajan
authors.affiliation: the Department of Pharmacology, University of Virginia Health System, Charlottesville, Virginia 22908, and.
authors.forename: Thurl E
authors.initials: TE
authors.lastname: Harris
authors.affiliation: From the Department of Nutrition, University of North Carolina, Chapel Hill, North Carolina 27599, rcoleman@unc.edu.
authors.forename: Rosalind A
authors.initials: RA
authors.lastname: Coleman
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D019852:Diacylglycerol Kinase / Q000235:genetics / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism*; D005992:Glycerol-3-Phosphate O-Acyltransferase / Q000235:genetics / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D010712:Phosphatidic Acids / Q000378:metabolism*; D010739:Phospholipase D / Q000235:genetics / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D004075:Diglycerides; D007328:Insulin; D010712:Phosphatidic Acids; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; C525637:rictor protein, mouse; D005992:Glycerol-3-Phosphate O-Acyltransferase; D019852:Diacylglycerol Kinase; D058570:TOR Serine-Threonine Kinases; D011493:Protein Kinase C; C105606:phospholipase D2; D010739:Phospholipase D; C106801:phospholipase D1
keywords: Diacylglycerol Kinase; Glycerol-3-phosphate Acyltransferase; Glycerophospholipid; Insulin Resistance; Mammalian Target of Rapamycin (mTOR); Phospholipase D; Protein Kinase C (PKC)