title: Deletion of Ia-2 and/or Ia-2β in mice decreases insulin secretion by reducing the number of dense core vesicles.
abstract: OBJECTIVE
  Islet antigen 2 (IA-2) and IA-2β are dense core vesicle (DCV) transmembrane proteins and major autoantigens in type 1 diabetes. The present experiments were initiated to test the hypothesis that the knockout of the genes encoding these proteins impairs the secretion of insulin by reducing the number of DCV.
  
  
  METHODS
  Insulin secretion, content and DCV number were evaluated in islets from single knockout (Ia-2 [also known as Ptprn] KO, Ia-2β [also known as Ptprn2] KO) and double knockout (DKO) mice by a variety of techniques including electron and two-photon microscopy, membrane capacitance, Ca(2+) currents, DCV half-life, lysosome number and size and autophagy.
  
  
  RESULTS
  Islets from single and DKO mice all showed a significant decrease in insulin content, insulin secretion and the number and half-life of DCV (p < 0.05 to 0.001). Exocytosis as evaluated by two-photon microscopy, membrane capacitance and Ca(2+) currents supports these findings. Electron microscopy of islets from KO mice revealed a marked increase (p < 0.05 to 0.001) in the number and size of lysosomes and enzymatic studies showed an increase in cathepsin D activity (p < 0.01). LC3 protein, an indicator of autophagy, also was increased in islets of KO compared with wild-type mice (p < 0.05 to 0.01) suggesting that autophagy might be involved in the deletion of DCV.
  
  
  CONCLUSIONS
  We conclude that the decrease in insulin content and secretion, resulting from the deletion of Ia-2 and/or Ia-2β, is due to a decrease in the number of DCV.
authors: Experimental Medicine Section, Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA. tcai@mail.nih.gov
authors: T
authors: T
authors: Cai
authors: H
authors: H
authors: Hirai
authors: G
authors: G
authors: Zhang
authors: M
authors: M
authors: Zhang
authors: N
authors: N
authors: Takahashi
authors: H
authors: H
authors: Kasai
authors: L S
authors: LS
authors: Satin
authors: R D
authors: RD
authors: Leapman
authors: A L
authors: AL
authors: Notkins
mesh_terms: D000818:Animals; D001343:Autophagy / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology; D005260:Female; D017353:Gene Deletion; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008854:Microscopy, Electron; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D023421:Models, Animal; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8 / Q000172:deficiency / Q000235:genetics*; D022142:Secretory Vesicles / Q000473:pathology* / Q000648:ultrastructure
chemical_list: D007328:Insulin; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; C516863:Ptprn protein, mouse; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D002402:Cathepsin D; D002118:Calcium