title: Glucose and palmitate uncouple AMPK from autophagy in human aortic endothelial cells.
abstract: Dysregulated autophagy and decreased AMP-activated protein kinase (AMPK) activity are each associated with atherogenesis. Atherogenesis is preceded by high circulating concentrations of glucose and fatty acids, yet the mechanism by which these nutrients regulate autophagy in human aortic endothelial cells (HAECs) is not known. Furthermore, whereas AMPK is recognized as an activator of autophagy in cells with few nutrients, its effects on autophagy in nutrient-rich HAECs has not been investigated. We maintained and passaged primary HAECs in media containing 25 mM glucose and incubated them subsequently with 0.4 mM palmitate. These conditions impaired basal autophagy and rendered HAECs more susceptible to apoptosis and adhesion of monocytes, outcomes attenuated by the autophagy activator rapamycin. Glucose and palmitate diminished AMPK activity and phosphorylation of the uncoordinated-51-like kinase 1 (ULK1) at Ser555, an autophagy-activating site targeted by AMPK. 5-Aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR)-mediated activation of AMPK phosphorylated acetyl-CoA carboxylase, but treatment with AICAR or other AMPK activators (A769662, phenformin) did not restore ULK1 phosphorylation or autophagosome formation. To determine whether palmitate-induced ceramide accumulation contributed to this finding, we overexpressed a ceramide-metabolizing enzyme, acid ceramidase. The increase in acid ceramidase expression ameliorated the effects of excess nutrients on ULK1 phosphorylation, without altering the effects of the AMPK activators. Thus, unlike low nutrient conditions, AMPK becomes uncoupled from autophagy in HAECs in a nutrient-rich environment, such as that found in patients with increased cardiovascular risk. These findings suggest that combinations of AMPK-independent and AMPK-dependent therapies may be more effective alternatives than either therapy alone for treating nutrient-induced cellular dysfunction.
authors.affiliation: Department of Medicine, Boston University School of Medicine and Boston Medical Center, Boston, Massachusetts karen.weikel@bmc.org.
authors.forename: Karen A
authors.identifier: http://orcid.org/0000-0003-0317-7891
authors.initials: KA
authors.lastname: Weikel
authors.affiliation: Department of Medicine, Boston University School of Medicine and Boston Medical Center, Boston, Massachusetts.
authors.forename: José M
authors.initials: JM
authors.lastname: Cacicedo
authors.affiliation: Department of Medicine, Boston University School of Medicine and Boston Medical Center, Boston, Massachusetts.
authors.forename: Neil B
authors.initials: NB
authors.lastname: Ruderman
authors.affiliation: Department of Medicine, Boston University School of Medicine and Boston Medical Center, Boston, Massachusetts.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ido
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D001011:Aorta / Q000187:drug effects / Q000502:physiology*; D001343:Autophagy / Q000187:drug effects / Q000502:physiology*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000008:administration & dosage*; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects; D006801:Humans; D019308:Palmitic Acid / Q000008:administration & dosage*; D014475:Uncoupling Agents / Q000008:administration & dosage
chemical_list: D014475:Uncoupling Agents; D019308:Palmitic Acid; D055372:AMP-Activated Protein Kinases; D005947:Glucose
keywords: AMPK; autophagy; endothelium; glucose; palmitate