title: Reciprocal regulation of mTOR complexes in pancreatic islets from humans with type 2 diabetes.
abstract: Mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of nutritional status at the cellular and organismic level. While mTORC1 mediates beta cell growth and expansion, its hyperactivation has been observed in pancreatic islets from animal models of type 2 diabetes and leads to beta cell loss. We sought to determine whether such mTORC1 activation occurs in humans with type 2 diabetes or in metabolically stressed human islets and whether mTORC1 blockade can restore beta cell function of diabetic islets.
  
  
  
  Human islets isolated from non-diabetic controls and individuals with type 2 diabetes, as well as human islets and INS-1E cells exposed to increased glucose (22.2 mmol/l), were examined for mTORC1/2 activity by western blotting analysis of phosphorylation of mTORC1 downstream targets ribosomal protein S6 kinase 1 (S6K1), S6 and eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1) and mTORC2 downstream targets Akt and N-myc downstream regulated 1 (NDRG1). mTORC1/2 complexes' integrity was assessed by immunoprecipitation and subsequent western blot analysis. Cell-type specific expression of activated mTORC1 in human islets was examined by immunostaining of pS6 (Ser 235/236) in human islet sections. Beta cell function was measured by glucose-stimulated insulin secretion (GSIS).
  
  
  
  While mTORC2 signalling was diminished, mTORC1 activity was markedly increased in islets from patients with type 2 diabetes and in islets and beta cells exposed to increased glucose concentrations. Under high-glucose conditions in metabolically stressed human islets, we identified a reciprocal regulation of different mTOR complexes, with functional upregulation of mTORC1 and downregulation of mTORC2. pS6 immunostaining showed beta cell-specific upregulation of mTORC1 in islets isolated from patients with type 2 diabetes. Inhibition of mTORC1-S6K1 signalling improved GSIS and restored mTORC2 activity in islets from patients with type 2 diabetes as well as in islets isolated from diabetic db/db mice and mice fed a high-fat/high-sucrose diet.
  
  
  
  Our data show the aberrant mTORC1 activity in islets from patients with type 2 diabetes, in human islets cultured under diabetes-associated increased glucose conditions and in diabetic mouse islets. This suggests that elevated mTORC1 activation is a striking pathogenic hallmark of islets in type 2 diabetes, contributing to impaired beta cell function and survival in the presence of metabolic stress.
authors.affiliation: Islet Biology Laboratory, Centre for Biomolecular Interactions Bremen, University of Bremen, Leobener Straße NW2, Room B2080, 28359, Bremen, Germany.
authors.forename: Ting
authors.initials: T
authors.lastname: Yuan
authors.affiliation: Islet Biology Laboratory, Centre for Biomolecular Interactions Bremen, University of Bremen, Leobener Straße NW2, Room B2080, 28359, Bremen, Germany.
authors.forename: Sahar
authors.initials: S
authors.lastname: Rafizadeh
authors.affiliation: Islet Biology Laboratory, Centre for Biomolecular Interactions Bremen, University of Bremen, Leobener Straße NW2, Room B2080, 28359, Bremen, Germany.
authors.forename: Kanaka Durga Devi
authors.initials: KD
authors.lastname: Gorrepati
authors.affiliation: Islet Biology Laboratory, Centre for Biomolecular Interactions Bremen, University of Bremen, Leobener Straße NW2, Room B2080, 28359, Bremen, Germany.
authors.forename: Blaz
authors.initials: B
authors.lastname: Lupse
authors.affiliation: Division of Transplantation, University of Illinois at Chicago, Chicago, IL, USA.
authors.forename: Jose
authors.initials: J
authors.lastname: Oberholzer
authors.affiliation: Islet Biology Laboratory, Centre for Biomolecular Interactions Bremen, University of Bremen, Leobener Straße NW2, Room B2080, 28359, Bremen, Germany. kmaedler@uni-bremen.de.|German Center for Diabetes Research (DZD) project partner, University of Bremen, Bremen, Germany. kmaedler@uni-bremen.de.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Maedler
authors.affiliation: Islet Biology Laboratory, Centre for Biomolecular Interactions Bremen, University of Bremen, Leobener Straße NW2, Room B2080, 28359, Bremen, Germany. ardestani.amin@gmail.com.
authors.forename: Amin
authors.initials: A
authors.lastname: Ardestani
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000328:Adult; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D047468:Immunoprecipitation; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D000076222:Mechanistic Target of Rapamycin Complex 1; D008875:Middle Aged; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D000099259:N-myc Downstream-Regulated Gene 1 Protein
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D005947:Glucose; D047908:Intracellular Signaling Peptides and Proteins; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D000099259:N-myc Downstream-Regulated Gene 1 Protein; C087000:EIF4EBP1 protein, human; C546842:MTOR protein, human; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1
keywords: Beta cells; Glucose; Human islets; Nutrients; Type 2 diabetes; mTORC1; mTORC2