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Activation of Protein Kinase C-ζ in Pancreatic β-Cells In Vivo Improves Glucose Tolerance and Induces β-Cell Expansion via mTOR Activation

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...

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Detalles Bibliográficos
Autores principales: Velazquez-Garcia, Silvia, Valle, Shelley, Rosa, Taylor C., Takane, Karen K., Demirci, Cem, Alvarez-Perez, Juan C., Mellado-Gil, Jose M., Ernst, Sara, Scott, Donald K., Vasavada, Rupangi C., Alonso, Laura C., Garcia-Ocaña, Adolfo
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Diabetes Association 2011
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3178296/
https://www.ncbi.nlm.nih.gov/pubmed/21911744
http://dx.doi.org/10.2337/db10-1783
Descripción
Sumario: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. RESEARCH DESIGN AND 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.