title: Deficiency of APPL1 in mice impairs glucose-stimulated insulin secretion through inhibition of pancreatic beta cell mitochondrial function.
abstract: OBJECTIVE
  Adaptor protein, phosphotyrosine interaction, pleckstrin homology domain and leucine zipper containing 1 (APPL1) is an adapter protein that positively mediates adiponectin signalling. Deficiency of APPL1 in the target tissues of insulin induces insulin resistance. We therefore aimed, in the present study, to determine its role in regulating pancreatic beta cell function.
  
  
  METHODS
  A hyperglycaemic clamp test was performed to determine insulin secretion in APPL1 knockout (KO) mice. Glucose- and adiponectin-induced insulin release was measured in islets from APPL1 KO mice or INS-1(832/13) cells with either APPL1 knockdown or overproduction. RT-PCR and western blotting were conducted to analyse gene expression and protein abundance. Oxygen consumption rate (OCR), ATP production and mitochondrial membrane potential were assayed to evaluate mitochondrial function.
  
  
  RESULTS
  APPL1 is highly expressed in pancreatic islets, but its levels are decreased in mice fed a high-fat diet and db/db mice compared with controls. Deletion of the Appl1 gene leads to impairment of both the first and second phases of insulin secretion during hyperglycaemic clamp tests. In addition, glucose-stimulated insulin secretion (GSIS) is significantly decreased in islets from APPL1 KO mice. Conversely, overproduction of APPL1 leads to an increase in GSIS in beta cells. In addition, expression levels of several genes involved in insulin production, mitochondrial biogenesis and mitochondrial OCR, ATP production and mitochondrial membrane potential are reduced significantly in APPL1-knockdown beta cells. Moreover, suppression or overexproduction of APPL1 inhibits or stimulates adiponectin-potentiated GSIS in beta cells, respectively.
  
  
  CONCLUSIONS
  Our study demonstrates the roles of APPL1 in regulating GSIS and mitochondrial function in pancreatic beta cells, which implicates APPL1 as a therapeutic target in the treatment of type 2 diabetes.
authors.affiliation: Department of Endocrinology and Metabolism, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, 600 Yishan Road, Shanghai 200233, People's Republic of China.
authors.forename: Chen
authors.initials: C
authors.lastname: Wang
authors.forename: Xiaowen
authors.initials: X
authors.lastname: Li
authors.forename: Kaida
authors.initials: K
authors.lastname: Mu
authors.forename: Ling
authors.initials: L
authors.lastname: Li
authors.forename: Shihong
authors.initials: S
authors.lastname: Wang
authors.forename: Yunxia
authors.initials: Y
authors.lastname: Zhu
authors.forename: Mingliang
authors.initials: M
authors.lastname: Zhang
authors.forename: Jiyoon
authors.initials: J
authors.lastname: Ryu
authors.forename: Zhifang
authors.initials: Z
authors.lastname: Xie
authors.forename: Dongyun
authors.initials: D
authors.lastname: Shi
authors.forename: Weiping J
authors.initials: WJ
authors.lastname: Zhang
authors.forename: Lily Q
authors.initials: LQ
authors.lastname: Dong
authors.forename: Weiping
authors.initials: W
authors.lastname: Jia
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000172:deficiency / Q000235:genetics*; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D005947:Glucose / Q000494:pharmacology*; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C510733:Appl1 protein, mouse; D005947:Glucose