title: The p21-activated kinase (PAK1) is involved in diet-induced beta cell mass expansion and survival in mice and human islets.
abstract: Human islets from type 2 diabetic donors are reportedly 80% deficient in the p21 (Cdc42/Rac)-activated kinase, PAK1. PAK1 is implicated in beta cell function and maintenance of beta cell mass. We questioned the mechanism(s) by which PAK1 deficiency potentially contributes to increased susceptibility to type 2 diabetes.
  
  
  
  Non-diabetic human islets and INS 832/13 beta cells cultured under diabetogenic conditions (i.e. with specific cytokines or under glucolipotoxic [GLT] conditions) were evaluated for changes to PAK1 signalling. Combined effects of PAK1 deficiency with GLT stress were assessed using classic knockout (Pak1 (-/-) ) mice fed a 45% energy from fat/palmitate-based, 'western' diet (WD). INS 832/13 cells overexpressing or depleted of PAK1 were also assessed for apoptosis and signalling changes.
  
  
  
  Exposure of non-diabetic human islets to diabetic stressors attenuated PAK1 protein levels, concurrent with increased caspase 3 cleavage. WD-fed Pak1 knockout mice exhibited fasting hyperglycaemia and severe glucose intolerance. These mice also failed to mount an insulin secretory response following acute glucose challenge, coinciding with a 43% loss of beta cell mass when compared with WD-fed wild-type mice. Pak1 knockout mice had fewer total beta cells per islet, coincident with decreased beta cell proliferation. In INS 832/13 beta cells, PAK1 deficiency combined with GLT exposure heightened beta cell death relative to either condition alone; PAK1 deficiency resulted in decreased extracellular signal-related kinase (ERK) and B cell lymphoma 2 (Bcl2) phosphorylation levels. Conversely, PAK1 overexpression prevented GLT-induced cell death.
  
  
  
  These findings suggest that PAK1 deficiency may underlie an increased diabetic susceptibility. Discovery of ways to remediate glycaemic dysregulation via altering PAK1 or its downstream effectors offers promising opportunities for disease intervention.
authors.affiliation: Department of Molecular & Cellular Endocrinology, Beckman Research Institute of City of Hope, 1500 E. Duarte Rd., Duarte, CA, 91010, USA.
authors.forename: Miwon
authors.initials: M
authors.lastname: Ahn
authors.affiliation: Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Yoder
authors.affiliation: Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Zhanxiang
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Molecular & Cellular Endocrinology, Beckman Research Institute of City of Hope, 1500 E. Duarte Rd., Duarte, CA, 91010, USA.
authors.forename: Eunjin
authors.initials: E
authors.lastname: Oh
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Latha
authors.initials: L
authors.lastname: Ramalingam
authors.affiliation: Department of Molecular & Cellular Endocrinology, Beckman Research Institute of City of Hope, 1500 E. Duarte Rd., Duarte, CA, 91010, USA.|Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Ragadeepthi
authors.initials: R
authors.lastname: Tunduguru
authors.affiliation: Department of Molecular & Cellular Endocrinology, Beckman Research Institute of City of Hope, 1500 E. Duarte Rd., Duarte, CA, 91010, USA. dthurmond@coh.org.|Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA. dthurmond@coh.org.|Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA. dthurmond@coh.org.
authors.forename: Debbie C
authors.initials: DC
authors.lastname: Thurmond
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D016923:Cell Death / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D049109:Cell Proliferation / Q000235:genetics / Q000502:physiology; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D018149:Glucose Intolerance / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006943:Hyperglycemia / Q000235:genetics / Q000378:metabolism; D015151:Immunoblotting; D066298:In Vitro Techniques; D050417:Insulin-Secreting Cells / Q000473:pathology; D007515:Islets of Langerhans / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D010766:Phosphorylation / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D054462:p21-Activated Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D054462:p21-Activated Kinases
keywords: Beta cell mass; Diet-induced obesity; Insulin secretion; PAK1; Prediabetes; Type 2 diabetes