title: DOC2 isoforms play dual roles in insulin secretion and insulin-stimulated glucose uptake.
abstract: OBJECTIVE
  Glucose-stimulated insulin secretion (GSIS) and insulin-stimulated glucose uptake are processes that rely on regulated intracellular vesicle transport and vesicle fusion with the plasma membrane. DOC2A and DOC2B are calcium-sensitive proteins that were identified as key components of vesicle exocytosis in neurons. Our aim was to investigate the role of DOC2 isoforms in glucose homeostasis, insulin secretion and insulin action.
  
  
  METHODS
  DOC2 expression was measured by RT-PCR and western blotting. Body weight, glucose tolerance, insulin action and GSIS were assessed in wild-type (WT), Doc2a (-/-) (Doc2aKO), Doc2b (-/-) (Doc2bKO) and Doc2a (-/-)/Doc2b (-/-) (Doc2a/Doc2bKO) mice in vivo. In vitro GSIS and glucose uptake were assessed in isolated tissues, and exocytotic proteins measured by western blotting. GLUT4 translocation was assessed by epifluorescence microscopy.
  
  
  RESULTS
  Doc2b mRNA was detected in all tissues tested, whereas Doc2a was only detected in islets and the brain. Doc2aKO and Doc2bKO mice had minor glucose intolerance, while Doc2a/Doc2bKO mice showed pronounced glucose intolerance. GSIS was markedly impaired in Doc2a/Doc2bKO mice in vivo, and in isolated Doc2a/Doc2bKO islets in vitro. In contrast, Doc2bKO mice had only subtle defects in insulin secretion in vivo. Insulin action was impaired to a similar degree in both Doc2bKO and Doc2a/Doc2bKO mice. In vitro insulin-stimulated glucose transport and GLUT4 vesicle fusion were defective in adipocytes derived from Doc2bKO mice. Surprisingly, insulin action was not altered in muscle isolated from DOC2-null mice.
  
  
  CONCLUSIONS
  Our study identifies a critical role for DOC2B in insulin-stimulated glucose uptake in adipocytes, and for the synergistic regulation of GSIS by DOC2A and DOC2B in beta cells.
authors.affiliation: Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia.
authors.forename: Jia
authors.initials: J
authors.lastname: Li
authors.forename: James
authors.initials: J
authors.lastname: Cantley
authors.forename: James G
authors.initials: JG
authors.lastname: Burchfield
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Meoli
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Stöckli
authors.forename: P Tess
authors.initials: PT
authors.lastname: Whitworth
authors.forename: Himani
authors.initials: H
authors.lastname: Pant
authors.forename: Rima
authors.initials: R
authors.lastname: Chaudhuri
authors.forename: Alexander J A
authors.initials: AJ
authors.lastname: Groffen
authors.forename: Matthijs
authors.initials: M
authors.lastname: Verhage
authors.forename: David E
authors.initials: DE
authors.lastname: James
mesh_terms: D017667:Adipocytes / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000235:genetics / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; C490418:Doc2a protein, mouse; C490421:Doc2b protein, mouse; D007328:Insulin; D009419:Nerve Tissue Proteins; D005947:Glucose