title: Activation of protein kinase C-ζ in pancreatic β-cells in vivo improves glucose tolerance and induces β-cell expansion via mTOR activation.
abstract: OBJECTIVE
  PKC-ζ activation is a key signaling event for growth factor-induced β-cell replication in vitro. However, the effect of direct PKC-ζ activation in the β-cell in vivo is unknown. In this study, we examined the effects of PKC-ζ activation in β-cell expansion and function in vivo in mice and the mechanisms associated with these effects.
  
  
  METHODS
  We characterized glucose homeostasis and β-cell phenotype of transgenic (TG) mice with constitutive activation of PKC-ζ in the β-cell. We also analyzed the expression and regulation of signaling pathways, G1/S cell cycle molecules, and β-cell functional markers in TG and wild-type mouse islets.
  
  
  RESULTS
  TG mice displayed increased plasma insulin, improved glucose tolerance, and enhanced insulin secretion with concomitant upregulation of islet insulin and glucokinase expression. In addition, TG mice displayed increased β-cell proliferation, size, and mass compared with wild-type littermates. The increase in β-cell proliferation was associated with upregulation of cyclins D1, D2, D3, and A and downregulation of p21. Phosphorylation of D-cyclins, known to initiate their rapid degradation, was reduced in TG mouse islets. Phosphorylation/inactivation of GSK-3β and phosphorylation/activation of mTOR, critical regulators of D-cyclin expression and β-cell proliferation, were enhanced in TG mouse islets, without changes in Akt phosphorylation status. Rapamycin treatment in vivo eliminated the increases in β-cell proliferation, size, and mass; the upregulation of cyclins Ds and A in TG mice; and the improvement in glucose tolerance-identifying mTOR as a novel downstream mediator of PKC-ζ-induced β-cell replication and expansion in vivo. CONCLUSIONS PKC:-ζ, through mTOR activation, modifies the expression pattern of β-cell cycle molecules leading to increased β-cell replication and mass with a concomitant enhancement in β-cell function. Approaches to enhance PKC-ζ activity may be of value as a therapeutic strategy for the treatment of diabetes.
authors.affiliation: Department of Medicine, Division of Endocrinology and Metabolism, University of Pittsburgh, Pittsburgh, USA.
authors.forename: Silvia
authors.initials: S
authors.lastname: Velazquez-Garcia
authors.forename: Shelley
authors.initials: S
authors.lastname: Valle
authors.forename: Taylor C
authors.initials: TC
authors.lastname: Rosa
authors.forename: Karen K
authors.initials: KK
authors.lastname: Takane
authors.forename: Cem
authors.initials: C
authors.lastname: Demirci
authors.forename: Juan C
authors.initials: JC
authors.lastname: Alvarez-Perez
authors.forename: Jose M
authors.initials: JM
authors.lastname: Mellado-Gil
authors.forename: Sara
authors.initials: S
authors.lastname: Ernst
authors.forename: Donald K
authors.initials: DK
authors.lastname: Scott
authors.forename: Rupangi C
authors.initials: RC
authors.lastname: Vasavada
authors.forename: Laura C
authors.initials: LC
authors.lastname: Alonso
authors.forename: Adolfo
authors.initials: A
authors.lastname: Garcia-Ocaña
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001786:Blood Glucose; D005786:Gene Expression Regulation / Q000502:physiology; D018149:Glucose Intolerance / Q000235:genetics / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D007328:Insulin / Q000097:blood / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D010766:Phosphorylation; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D000099221:Protein Kinase C zeta
chemical_list: D000900:Anti-Bacterial Agents; D001786:Blood Glucose; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D007328:Insulin; D011493:Protein Kinase C; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D000099221:Protein Kinase C zeta; C546843:mTOR protein, mouse; C000605507:Gsk3b protein, mouse